# A 15cc sidevalve opposed twin



## Peter Twissell (Nov 7, 2021)

Combining my hobbies of RC model flying and model engineering, I have designed an engine for my next aircraft model.
The aircraft is a well established design (Chris Foss Acro Wot) and is intended to use engines from 6cc 2 stroke to 15cc 4 stroke.
I don't hold out hope for impressive power output from my design, so I have gone for the upper end of the engine displacement range.
I have decided on a sidevalve layout, both for simplicity and to keep the overall width of the engine within the model's cowling.
My design uses a pressed together crankshaft assembly with one piece connecting rods.
The main structure of the engine consists of two identical 'blocks', machined from aluminium with iron liners for the cylinder bores.


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## Peter Twissell (Nov 7, 2021)

The block half has the iron liner and bronze valve cages pressed into shouldered bores. The pair of block halves is bolted together and bored through for the crankshaft and camshaft.


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## Peter Twissell (Nov 7, 2021)

The Crankshaft is supported by ballraces mounted into the end covers, which locate in the large bore through the blocks.
The camshaft is supported by ballraces which are captured directly in the smaller bore.


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## Peter Twissell (Nov 7, 2021)

I have already started manufacture.
The photo shows one of the blocks with the liner installed and most of the machining completed. The liner bore is undersize and will be finished as the final operation, after the valve cages are pressed in and all other machining is complete.
Apologies for the poor quality of my photos!


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## Peter Twissell (Nov 7, 2021)

A little more detail on the engine design; the bore and stroke are 21mm and 22mm respectively. The valves are 9mm diameter with 3mm lift. The combustion chamber is the well-established heart shape. The engine will run on methanol with glow plug ignition. Running on methanol significantly reduces the heat rejection issues, especially around the exhaust valve area in sidevalve designs.

The total weight of the engine 'firewall forward' i.e. including carburettor, exhaust system and mount, is 728g (calculated in CAD). My CAD model is created in Fusion 360 and I have included every nut, screw and clip, each represented in their correct materials.
For comparison, an OS90 4 stroke weighs 703g with exhaust but without mount, so I am happy with that.

The camshaft has only three cams. The middle cam operates both intake valves. The other two cams operate the exhaust valves.
Lubrication will be similar to the majority of 4 stroke model aircraft engines, using oil in the fuel and relying on blow-by to get it into the crankcase space. A vent in the timing gear case will allow excess oil to escape and crankcase pressure to be relieved.


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## Peter Twissell (Nov 7, 2021)

I have yet to decide on how to produce the induction and exhaust pipes. Both are 8mm bore, 10mm OD and require bends at 1D (i.e. 10mm centreline bend radius).
For my larger engines, I have been able to purchase stainless steel 'dairy tube' mandrel bends at 1D, but I have not been able to find such bends in smaller sizes.
The options I am considering are:
1) Manufacture a suitable miniature pipe bender with a mandrel and make the pipes from copper.
2) Use the lost PLA method, 3D printing the parts and casting in bronze. I have no experience with lost PLA casting. From what I have read, bronze is among the easiest metals to cast.

Any suggestions welcome!

I am currently leaning towards making a mandrel bender, not least because I like to make tools


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## Peter Twissell (Nov 7, 2021)

Part of the reason for building this engine is as a practise run before I start on a Whittle V8.
I have never made anything this small and my previous engines have used commercially available piston rings.
I intend to use the Trimble method to produce rings, as detailed in the Whittle V8 build articles. I will also use Eric Whittles instructions on manufacture and use of an iron cylinder hone.


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## Ken I (Nov 8, 2021)

Pete - I'll be watching closely - always wanted to design a 4-stroke.
Blow by lubrication in the fuel ? Will crankcase vent be to waste or to inlet to "burn off" ?
Are you going to key the pressfit crank, square, round or doweled ?
Suggestion for exhausts - I worked for an electronic company where we made Copper wave guides with a tapered rectangular bore with razor sharp internal corners - if you looked closely you could see circular machining marks right into the internal corners which puzzled the hell out of most people.
We did this by making a male mandrel from cerrobend - we electrolytically copper plated it for 48 hours and then machined the outside from datum holes in the cerrobend - plugged with wax for later mounting points (After 48 hours of plating the coated mandrel looked like a brown Kiwifruit). We also attached perspex blocks to the mandrel to provide all the holes, windows and grilles required without further machining.
You can plate onto a heavier flange (pre-machined) - laquered where you don't want to plate.
After machining the outside - we simply melted out the cerrobend - the machining marks remained evident on the female inner surfaces - right up to the sharp corners - very puzzling unless you knew how it was done.
Wall thickness after machining was ±2.5mm - I don't think you are going near that but it might be an interesting method to explore.
Where the bore shape permitted (no rentrant angles) we used steel mandrels which were knocked out an reused - they were coated with some sort of conductive release agent - unfortunately I can't remember what that was.
You might get away with using a 3D printed PLA plastic former and premachined Copper flange - after plating the tube to thickness you just decompose the PLA in an oven.
The surface finish might cause poor plating to thickness - so maybe just a piece of heat formed rod.
These days, I think plating with what is termed "self-leveling" Copper plate - you should be able to plate to an appropriate thickness without having to touch the surface afterwards.
Most people don't get that Copper has a high melting point = 1085°C.
Regards, Ken


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## Peter Twissell (Nov 8, 2021)

Hi Ken,
Thanks, I hadn't considered electro deposition. I'm not sure it is possible to build up 2.5mm thickness (typo?) But it's worth me trying some test parts. I would make the cores from white metal, which can be accurately cast in silicon rubber moulds, which in turn can be made from 3D prints.
Blow by lubrication is the norm in model aircraft 4 strokes. I'll start with some oil in the cases anyway and monitor the vent, which will simply exit to atmosphere.
The pressed crank assembly will not be keyed, following common practise in motorcycle 2 stroke engines.


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## Ken I (Nov 8, 2021)

Pete, We built up way more than 2.5mm - that was the finished thickness - we actually built it up to about 4mm to ensure we had enough material everywhere otherwise it would be scrap.
The build-up was quite uneven (especially over sharp corners) but I know there are much better self-leveling copper plating solutions out there today.
I would start with a straight rod for simplicity, next add a flange - once you have all the bugs doped out, go to the actual parts. (There's always going to be bugs.)
The plating was done in our in-house facility - I had nothing to do with that - but they weren't terribly sophisticated in those days (early 70's) - we (in the model shop) referred to them as the "Chemical Milling Department" because of the number of precision parts they etched undersize.
I know about motorcycle cranks I used to mechanic for various racers for a number of years - we even assembled a 250 2-stroke twin so both cylinders fired together (the owners idea not mine - I didn't approve) and he called it a "twingle".
I was just curious as to how that works when scaled down.
Regards, Ken


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## Peter Twissell (Nov 8, 2021)

I'm impressed that they could build up that much copper in such a relatively short time. I am used to plating build up in a few thousandths of an inch per hour.
The 'twingle' thing was and still is popular with some racers. I am told it gives them better feedback at the limit of grip.


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## Ken I (Nov 8, 2021)

It was an electrolytic process which tends to deposit way faster than current electroless types. And yes - typically only 2 thou an hour - so maybe they pushed it a lot but sooner or later that causes trouble and you end up with a pineapple. I never actually watched the process I was only involved in the machining processes and the 48 hours was a "throwaway line" of dialogue and of course my memory might be faulty.
But we did make 'em this way.
Regards, Ken


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## Peter Twissell (Nov 8, 2021)

Thanks Ken, definitely worth further investigation.


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## awake (Nov 8, 2021)

Peter, I love the look of this - looking forward to seeing it take shape and run!


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## propclock (Nov 8, 2021)

machine botherer. I like that , 
I often think of myself as a machine Racoon, 
I can't "see" it if I can't touch it.  Great project.


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## Peter Twissell (Nov 15, 2021)

More swarf has been made.
The cylinders now have cooling fins. They're not very deep, but based on other glow ignition engines of similar size, should be sufficient.
Valve cage have been made and pressed into the cylinder blocks.


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## Peter Twissell (Nov 15, 2021)

Next is the valves.
The photo shows the "blanks", with the valves head OD finished, the neck machined and the clip groove finished.
The valve stems are left 0.005" oversize and will be finished at the same setting as the seat angle, with the aid of a traveling steady. Final size and finish will be achieved with a lap.


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## Peter Twissell (Nov 27, 2021)

More progress:
To finish the valve stems and seats, I set up a travelling steady, cut the seat with the cross slide rotated to 46 degree angle and then advanced the tool to finish the the stem diameter. With both machined at the same setting, they should be concentric.


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## Peter Twissell (Nov 27, 2021)

To finish the valve faces after parting off, I had to make a split collet. The neck of the valve is 2.5mm diameter.
The collet grips the valve on the neck, but also provides support on the back face of the head.


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## Peter Twissell (Nov 27, 2021)

Valve cages are a simple turning job. The OD was turned to a press fit in the bore in the block and the internals finished at the same setting.
As with the valves, this ensures concentricity of the critical features. The gas flow cavity was cut with an 8mm ballnose endmill.


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## Peter Twissell (Nov 27, 2021)

With the valve cages fitted, the ports are cut through the block and into the cage. The ports are counterbored for a small high temperature O ring which will seal against the manifold face. The M3 tapped hole below the ports will hold a clamp to retain both inlet and exhaust manifolds.
With the valves in place and open, there is a clear path for gas flow.


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## Peter Twissell (Nov 27, 2021)

After Ken kindly suggested electroforming, I have looked into it and decided it is the way ahead for the manifolds.
I will be 3D printing the formers in water soluble PVA and painting them with graphite paint before plating.
Since this process affords considerable freedom of design, I have taken the opportunity to relocate the carburettor to behind the cases, where it sits neatly inside the engine mount while still being able to access all the adjusters, fuel feed etc.
I have also re-routed the exhaust pipes, so that the installation in the model's cowling is neater.
The intake manifold will require a couple of features which cannot practically be electroformed, but those parts can be machined in brass and silver soldered into place.
I will finish the electroformed copper parts with a few microns of electroless nickel, just because I can!


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## Ken I (Nov 28, 2021)

Peter, Very cool - hope it all goes well and will be looking forward to the results.
(Somewhat anxiously, having steered you in that direction - it had better work.)
It sounds like you have been doing your homework.
IIRC when starting with a conductive paint - the initial deposition rate (current) is deliberately low and increased as the plate thickness increases - hence more current carrying capacity.
Regards, Ken


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## Peter Twissell (Nov 28, 2021)

Thanks Ken. I am planning to plate at a relatively low current anyway, in order to get a good finish and even thickness.


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## Ken I (Nov 28, 2021)

When you plate irregular, long or sharp cornered objects (the end of a tube is a sharp corner at the end of a long object - thus a double whammy) it is common practice to jig the part with "thief" electrodes - like a wire ring off the end of the tube - or an extension beyond the end of the tube.
This to have the overplate at the corner (caused by increased current density at that point) reduced or "stolen" by the "thief" - or have it occur on an extension portion to be cut off and/or discarded..
But I am sure you will stumble over this in your research.
Whilst you will probably find published guidelines - it is something of a black art - you would do well to talk it over with an experienced electroplater.
Regards, Ken


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## Peter Twissell (Nov 28, 2021)

Thanks for the advice, Ken.
I have modelled the first parts with an extra 5mm length on each end for exactly the reason you state.


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## Ken I (Nov 28, 2021)

Hmmm.... I should have known better than to teach you to suck eggs - I would just hate to see it go pear shaped for something I might have cautioned you against.
That said - this forum isn't just for us - hopefully others get to take something else away from this.

Regards, Ken


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## Peter Twissell (Nov 28, 2021)

You are only telling me what I just learnt 5 minutes ago!
I shall detail the process for the benefit of everyone on the forum.


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## propclock (Nov 28, 2021)

Thanks to both of you , electroplating is a new skill I would like to learn.


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## Peter Twissell (Dec 13, 2021)

Crankshaft.
The crankshaft is first turned as a 'blank' with the main journals oversize and with excess length.


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## Peter Twissell (Dec 13, 2021)

I then drilled an reamed the holes for the offset journals and machined the counterbalance forms.


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## Peter Twissell (Dec 13, 2021)

Connecting rods are fairly straightforward, much of the machining done on the rotary table.


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## Peter Twissell (Dec 13, 2021)

The spaces between the webs are partially machined, sufficient to allow assembly of the rods, but leaving the crankshaft as one piece.
The offset journals are hard dowel pins.
Here the assembly is shown with over-length pins pressed into place before trimming to length with an abrasive wheel in a Dremel.


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## Peter Twissell (Dec 13, 2021)

Since this engine is intended to be used in a flying model, it is inevitable that at some point the prop will strike the ground, causing shock loading of the crankshaft.
With this in mind, I have decided to bolster the pressed up crankshaft assembly with a few tacks of TIG welding to lock the offset journal pins in place.
If I were building the engine just for running on a test stand, I would be confident of the pressed assembly without welding.

As an additional measure, I have decided that rather than the prop shaft being an integral part of the crankshaft, I will cut the crankshaft down to just ahead of the front bearing and drill and tap it for a separate prop shaft, which can be replaced if it is bent or broken.


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## a41capt (Dec 14, 2021)

Nice work Pete.  I love the design, and can’t wait to hear your first run!

John W


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## Peter Twissell (Dec 15, 2021)

Crankshaft assembly:


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## Peter Twissell (Dec 15, 2021)

The front cover of the engine supports two ballraces.
In the first operation on the cover, I turned the register which fits into the main bore of the pair of blocks and bored the through hole and one bearing housing.
To ensure that the bores are aligned, I made a fixture which locates on that first bearing housing with an expanding 'collet' to grip in the through bore.
The other end of the fixture (in the chuck here) is sized to fit in the bore of my rotary table, so it can also be used for the milling operations.


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## Peter Twissell (Dec 15, 2021)

The turned blank for the front cover is seen here mounted on the fixture, with the second bearing housing bored and the external profile machined. There is a slight taper on the 'nose' diameter, which was generated by rotating the cross slide. My Drummond Roundbed lathe does not have a top slide, but the cross slide can be rotated, providing 3" of taper turning travel.


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## Peter Twissell (Dec 15, 2021)

The parts so far temporarily assembled.
It is at this point that it became apparent that I need to machine some small clearances into the blocks to allow for the swing of the rods.
I'm not sure how I missed this in the CAD model!
Fortunately, the clearance required is only small and easily achieved without impacting any other aspects of the design.


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## Peter Twissell (Dec 19, 2021)

Rear cover / timing gear housing:
This part took me the best part of 2 days, mostly on the rotary table, and my entire vocabulary of expletives.
At the first attempt, I milled straight across one of the small lugs at the bottom. The part was otherwise 90% complete at that point.
The small holes are tapped M1.6.


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## Peter Twissell (Dec 19, 2021)

Pistons are relatively straightforward.
I made a fixture from two scraps of aluminium stock, bored to form a pair of clamps to hold the pistons for the milling operations.


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## a41capt (Dec 19, 2021)

Wow Pete, that’s an amazing bit of machine work Pard, and I’m sweating bullets when I have to tap 4-40, let alone anything as small as those tapped holes.  How many set ups did that part require?  BTW, I feel your pain.  I’ve also spent hours on a part only to find that my overzealous twirling of hand wheels has ruined all the previous work… 
John W


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## Peter Twissell (Dec 19, 2021)

Thanks John. M1.6 is the same size as 10BA, for those more familiar with traditional model size threads.
I hold the tap in a pin chuck and turn it with finger grip only, no tommy bar.
It helps that the 2014 aluminium is nice and crisp. Tapping soft materials can be troublesome, copper being among the worst.
The timing gear housing was machined with just three setups.
First, I bored the hole through and the bearing bore in the lathe, then turned the register which fits into the main blocks, all at one setting.
Next, I bolted a scrap of aluminium plate to the rotary table and machined a register to fit the through hole. With the part bolted to the fixture, I machined all the features which are concentric with the main bore, then at the same setting, bored the offset hole for the camshaft to pass through.
Finally, I re-machined the fixture so I could mount the part by the offset bore and machine the features which are concentric to that.

My drawings for parts like this consist of 2 or 3 sheets. The first details the part as designed, while further sheets show the polar co-ordinates for all the blend radii, beginning and end of each orbital cut etc. All the information I need to make the part on the rotary table.


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## Bentwings (Dec 24, 2021)

Peter Twissell said:


> With the valve cages fitted, the ports are cut through the block and into the cage. The ports are counterbored for a small high temperature O ring which will seal against the manifold face. The M3 tapped hole below the ports will hold a clamp to retain both inlet and exhaust manifolds.
> With the valves in place and open, there is a clear path for gas flow.


you’ve done a nice job so far. I’m a very long time madel plane builder and flyer oing back to early days of free flight then u control. Ultimately Rc and giant scal warbirs. My big Corsair flew for over 13 years. As with full scale I kept flight logs and maintenance logs and testing and research logs. My flight log book was over two inches thick. Most war birds  flyers are detail nuts one of my sons internet friends has gone so far as to put scale foot prints on he wing walks and hand marks on the hand grip ports. I won 5 scale events which involve static judging and flying in scale appearing flight. So I had my 5 kill flags displayed.  Early on I was a semi pro drag racer in both dragster and funny car. While not a money maker there was a positive balance in the check book . In both models and Rc I was known for running on “kill or the edge” I destroyed many early glow engines with loads of nitro and wild rpm often using custom tuned props. Misdeeds my own model fuel a long time ago as I had ready access to alcohol and nitromethane.  So that out of the way I’ll try and give some tips.  I also got into scale functioning exhaust and muffled tuned pipes. If you ar going to run alcohol and oil mix plan on plenty of compression  I think I’d opt for various thickness gashead gasket. You can calculate compression ratio obviously fine adjustments in thickness of gasket might not be possible we used .001 differences for example but sheet like this is not available unless you make a special rolling press. Instead I’d mak a spacer that you can replace at will. Then having run glow for year and burning glow plugs up by the pound rather than having only a couple spares I think I might look at using two plugs per cylinder and running battery power on in flight. Engine out or one balky cylinder in big planes I’d invitation to bad things.  Next exhaust. I’m not sure hat the electro….. I’d I’m thinking maybe 3D printed metal . That would be ok. Here is what I’d do as long as you are accomplished fusion user. I made fabricated p 51 exhausts out of thin stainless sheet TIG welded. I did presidium TIG welding so while very tedious did work. Later I neede to simplify and design for mfg. I modeled standard copper tube fittings then did weight calculation on cad. Then looked at trimming the fittings to minimums and both silver solder and braised the systems together using slip joints as necessary. You can trim fitting with aviation snips if you are carefull. Please , please don’t do the hack saw and vice as seen on so many videos. Copper gets pretty hot when welding or silver soldering simply chilling in water well remove a lot of scal and Anne at it at the same time don’t eve waste time with acid or rosin standard solder the exhaust temp will melt it . Be aware of pipe centerline length it has to do with tuning at least make it equal side to side you can alter fitting angle at will by cutting and welding or brazing I was able to trim about 65% of the weight by doing this. Because the brazing is so thin it really doesn’t count. Next I’d run dual plugs you may have to do a little rework but you can easily do this it loos like. Working in the auto machine shop I got to build a lot of engines from the ground up . I also worked at intl diesel that made Ford Diesel engines I ran the cylinder hone area. The blocks came in machined with .003” left in the bores for honing. There was rough gone to remove about .002 then the second stage was sizing that took them to about .001 with .001 or less for plateau hone and final size. This was exactly what we used in the auto shop. So try to do this even if you have to send the cyl out. Unless you want to try honing your self. Sun Ben is the great name in honing and I had good success with cyst. Support it’s a messy job if don’t have the right machin but it give perfectly straight bores with optimum finish. Your crank sounds nice. That’s standard construction  I’m not real familiar with slide valves excep steamers the fit needs to be good there too.  As for fuel klotz make good oil. I just did some research on steam oil as it’s not readily available here but castor oil is I just got a quart.  It’s possible to use canola oil too. Castor is still used in modern piston engine breaking on new and rebuilt engingines  amzoil has good synthetic. You might have to call support for recommendations.  Keep up the nice work I’ll try and follow you . 
byron


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## Peter Twissell (Dec 24, 2021)

Hi Byron and thanks for all the tips.
I'm also involved with drag racing, as part of a small group running pre-unit Triumph motors. We are currently rebuilding a bike with two 500cc motors, which still holds a class land speed record. We intend to drag race it for a season, then attempt to beat it's standing record.

My 15cc engine is not intended to make a huge amount of power. It's going into an Acro-Wot, which can take anything from a 6cc two stroke to a 15cc four stroke. I'm not going for high nitro or tuned pipes. The electroformed pipes will be in copper.


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## Peter Twissell (Dec 24, 2021)

The camshaft is quite simple, having only 3 lobes. The centre lobe operates both inlet valves and the other operate the exhaust valves.
The turned blank is set up in the dividing head and supported with a tailstock on the mill to generate the simple, flat flanked profiles.


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## Peter Twissell (Dec 24, 2021)

With the cams machined, the part is returned to the lathe to finish the ends.
Despite its apparent simplicity, I still managed to make the first one wrong, with 16 degrees of 'underlap' instead of the intended overlap!


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## Peter Twissell (Dec 24, 2021)

Parts made so far partially assembled.


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## Drawfiler (Dec 25, 2021)

Peter
Back to the pipes, you could try Cerrobend inside commercial tube.


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## Peter Twissell (Dec 25, 2021)

The electroforming thing has become a project now!
I'm keen to explore the possibilities of the process and I already have some ideas for other applications, including water jackets and radiators for water cooled engines.


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## Majormallock (Dec 25, 2021)

Peter Twissell said:


> Hi Byron and thanks for all the tips.
> I'm also involved with drag racing, as part of a small group running pre-unit Triumph motors. We are currently rebuilding a bike with two 500cc motors, which still holds a class land speed record. We intend to drag race it for a season, then attempt to beat it's standing record.
> 
> My 15cc engine is not intended to make a huge amount of power. It's going into an Acro-Wot, which can take anything from a 6cc two stroke to a 15cc four stroke. I'm not going for high nitro or tuned pipes. The electroformed pipes will be in copper.


Hi, Peter, I am building a Forrest Edwards 5 cylinder radial and having trouble with the inlet tubes 9/32 thin wall brass. I have bought some cerrobend for a final attempt,  but if that fails I was wondering if electroforming might work, reference the picture do you think it will work?


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## Peter Twissell (Dec 25, 2021)

I haven't tried the electroforming process yet, but I have seen complex electroformed parts and I have read a lot about the process, so I am confident that it is possible.
Watch this space, I will detail my process, warts and all!


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## Ken I (Dec 25, 2021)

Majormallock said:


> Hi, Peter, I am building a Forrest Edwards 5 cylinder radial and having trouble with the inlet tubes 9/32 thin wall brass. I have bought some cerrobend for a final attempt,  but if that fails I was wondering if electroforming might work, reference the picture do you think it will work?View attachment 132175


There are several tube bending tips and devices on the site - conduct a search.
Here's mine - note bending of 1/8" NOS lines.
Wire & Tube Bender
The ACAD plans are available as a Zip file here :-
https://www.homemodelenginemachinist.com/threads/wire-tube-bender.29079/
Regards, Ken


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## Richard Hed (Dec 26, 2021)

Majormallock said:


> Hi, Peter, I am building a Forrest Edwards 5 cylinder radial and having trouble with the inlet tubes 9/32 thin wall brass. I have bought some cerrobend for a final attempt,  but if that fails I was wondering if electroforming might work, reference the picture do you think it will work?View attachment 132175


Can you tell us your process for bending the tubes?


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## Majormallock (Dec 26, 2021)

Hi Richard. What i have tried so far is to anneal the tube, first of all by direct flame from my oxy/acc torch, then by 2 hour soak in my solid fuel fire. Air cooled, not quenched. I then made a tube bending small hand operated machine . Formers to clamp the straight part then bent found another half round former followed round by another former. In other word a small version of a standard none mandrel tube bender. All formers to exact 9/32 od. . Think I might have to upgrade to thicker wall copper, but I don't like to be beaten in the workshop, so next I have some cerrobend which I will try in the same bender. I am also in the process of buying some spring wire to make an internal support spring


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## Richard Hed (Dec 26, 2021)

Majormallock said:


> Hi Richard. What i have tried so far is to anneal the tube, first of all by direct flame from my oxy/acc torch, then by 2 hour soak in my solid fuel fire. Air cooled, not quenched. I then made a tube bending small hand operated machine . Formers to clamp the straight part then bent found another half round former followed round by another former. In other word a small version of a standard none mandrel tube bender. All formers to exact 9/32 od. . Think I might have to upgrade to thicker wall copper, but I don't like to be beaten in the workshop, so next I have some cerrobend which I will try in the same bender. I am also in the process of buying some spring wire to make an internal support spring


Did you fill the tubes with sand?  Try that, then bend them.  I know this works if it is carried out correctly.


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## Majormallock (Dec 26, 2021)

Hi, no I didn't  couldn't get fine enough sand , thats why I bought the cerrobend, but if you recommend,  I will try it. Many thanks


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## Richard Hed (Dec 26, 2021)

Majormallock said:


> Hi, no I didn't  couldn't get fine enough sand , thats why I bought the cerrobend, but if you recommend,  I will try it. Many thanks


Absolutely try it.  What is cerrobend?


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## petertha (Dec 26, 2021)

I'm eagerly awaiting Peter's electroforming results because that would have so many other useful applications in model engineering. Keep us posted!

For those of you struggling with 'conventional' bends & are not opposed to aluminum, I've had good results with 3003 alloy aluminum tube which goes under a label 'Versatube' at N-Am FS aircraft distributers. There may be other suppliers of similar alloy, maybe under a different label? My radius was formed with conventional commercial tool & flared with home made tool, without the need for heat or filler which I was trying to avoid. I suspect as the radii decreases, this alloy too may have its limits. But its a very inexpensive material to try. Exhaust tubes would be a different matter of course, but thought I'd mention this.








						3003-O Versatube | Aircraft Spruce Canada
					

3003-O Versatube Soft aluminum tubing for instrument air and vacuum lines, fuel and oil lines, and primer lines




					www.aircraftspruce.ca


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## Peter Twissell (Dec 26, 2021)

I now have a pair of 3D printed cores on which to form a pair of exhaust pipes.
I expect to be making my first attempts at electroforming in the coming week.

Re. Aluminium tube, I would not rule out using it for exhaust pipes on a glow ignition engine. Most model aircraft glow engines use cast alloy exhausts successfully.


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## Majormallock (Dec 26, 2021)

Richard Hed said:


> Absolutely try it.  What is cerrobend?


Hi, also know as Woods metal, its a very low melting point metal that can be poured into a tube at about 180f, it then solidifies so you can bend the tube then heat it up and pour it out


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## ytrose2 (Dec 27, 2021)

Regarding a fill material for the tubes before bending - I followed a tip I read elsewhere and got a 1l tub full of the waste grit after shotblasting. This is the fine stuff filtered out of the blasting circuit. I sieved this through a teastrainer, which gave me very fine material. After pouring into my tubing and sealing both ends, there was no collapsing of the tubing when bent.


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## Mike Ginn (Dec 27, 2021)

Hi.  I have never had success with sand.  I have also tried ground glass which I use in my "sand blaster".  This is 1 micron gauge but it still moves in the tube.  When I have tried to use it I have capped the tube ends to keep the sand/glass locked in place.  I have also used screws in the cap to add compression.  My greatest success has been using lead as a filler.  I think there is a low melting point metal alloy which would be better but I don't have any.  The lead can be reheated and either blown out of the tube or allowed to run out (safety issues etc).  Hope that helps
Mike


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## Majormallock (Dec 27, 2021)

Mike Ginn said:


> Hi.  I have never had success with sand.  I have also tried ground glass which I use in my "sand blaster".  This is 1 micron gauge but it still moves in the tube.  When I have tried to use it I have capped the tube ends to keep the sand/glass locked in place.  I have also used screws in the cap to add compression.  My greatest success has been using lead as a filler.  I think there is a low melting point metal alloy which would be better but I don't have any.  The lead can be reheated and either blown out of the tube or allowed to run out (safety issues etc).  Hope that helps
> Mike


Hi, Mike, any input helps, thanks. The low melting point metal you refer to is known as cerrobend to the trade and generically called Woods metal. I have manage to aquire a small amount, but also have access to a sand blaster with fine grit. I will try both methods till it works


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## Harglo (Dec 27, 2021)

Majormallock said:


> Hi, no I didn't  couldn't get fine enough sand , thats why I bought the cerrobend, but if you recommend,  I will try it. Many thanks


I have been successful with filling the tube/s with solder. Doesn't take too much heat to re melt out.
Harvey


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## skylark (Dec 27, 2021)

You could try the outer sheath of an old electric immersion heater,   it's normally stainless steel  - and pre bent to quite a tight radius at the ends and straight lengths as required for further small bends as needed.  The double loop type are better and you can get 4 or 5 pipes made up.


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## Mike Ginn (Dec 27, 2021)

Hi Majormallock.  Woods metal was the material I couldn't remember.  Probably better than lead since I understand it doesn't stick to the sides of the tube.  Lead or solder (without flux) does tend to leave deposits.  When I wanted to tightly bend copper tube (10mm dia) I made 2 silver soldered end caps with a M6 thread.  I then filled the tube and tightened up the M6 cap head screws to ensure compression.  It worked but I can't remember the rad I achieved.  I did however get better results with lead and it was easier.  Best of luck and I will be interested in the result.  Good project for Christmas!
Mike


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## Steamchick (Dec 27, 2021)

I have had success with both lead solder and candle wax for filling copper and brass tubes for bending. I have some simple hand benders, but they do the job well.
I did read of someone who crimped one end of a tube in the vice, filled the tube with water, then crimped the other end, and had successfull bending. But there must be no air inside the tube, and hydraulic sealing at the crimp.
K2


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## methuselah1 (Dec 28, 2021)

I have a "brick" of low melting point alloy, which I have used on occasion. When I say "low" m.p. I mean you can melt it back out with boiling water in an old saucepan. However, my stuff contains bismuth, and EXPANDS (a lot) on cooling- its use is carefully considered before each job.

Has anyone mentioned paraffin wax yet?


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## Rustkolector (Dec 28, 2021)

According to a "How Its Made" video they make trombone brass tubing bends by annealing the tube, filling it with water, freezing it, and bending in a standard looking tubing bender. If needed, the inside diameter of the bend can be maintained by ball sizing which would require a die to hold the bend. I have never tried this method but they make it look easy. Go to 2:45 of the video.
Jeff


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## Majormallock (Dec 28, 2021)

Loved the video, ball bearing method very clever.  Frozen water worth a try!  Not heard of paraffin  wax, I'll put it on the list if all else fails


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## Peter Twissell (Dec 30, 2021)

Timing gears are made from purchased 1.0 mod EN8 gears, parted off to 4mm thickness. The 30T gear is relieved on both sides and drilled to reduce weight.


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## Peter Twissell (Dec 30, 2021)

Valve springs are wound on a mandrel in the lathe, using the screwcutting gear to generate the pitch.


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## Peter Twissell (Dec 30, 2021)

Aluminium spring caps are counterbored to lock E clips to the valve stems.
Assembling the valve springs, caps and clips is fiddly, the only access being the 9mm bore in which the tappet will run.
I could have provided access through the underside of the block, but that would require a cover and fasteners - more weight.


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## Peter Twissell (Dec 31, 2021)

Electroforming:

A few members have expressed an interest in this process, so I shall endeavour to describe my efforts in as much detail as possible.
There are numerous websites which detail the process. I have been using this one: Electroforming Resources for Aspiring Artists

My patterns for the first couple of test pieces are 3D printed in PVA resin, which is soluble in water, making for (hopefully) easy removal when the plating is complete. The parts are built with the minimum of material, i.e. single layer wall thickness and just enough internal support structure to enable a successful print.

One end of each part is pierced and a copper wire (recovered from old domestic wiring) is pushed in. This will form the electrical conductor for plating, and will also support the part in the tank.


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## Peter Twissell (Dec 31, 2021)

The patterns are painted with conductive paint, covering only the surface to be plated, with the addition of a generous 'stripe' connecting the area to be plated to the copper wire.
The end faces do not require plating, but the PVA material will begin to dissolve when it is immersed in water, so it is necessary to cover the ends. For this purpose, I used matt black enamel paint, just because it was to hand and is fairly quick drying.
The conductive paint dries very quickly.

Shown here are the painted patterns, supported in the tank (HDPE ice cream tub) along with the anode, which is a length of 15mm copper domestic plumbing pipe.

The surface area of the anode needs to be approximately twice that of the cathode. The cathode surface area is the total of the parts to be plated.
The cathode surface area also needs to be known in order to calculate the plating current. This pair of parts will require 0.8 Amperes.


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## Peter Twissell (Dec 31, 2021)

For general guidance, pictured here is the kit required:
De-ionised water
Copper sulphate pentahydrate
Battery acid
Conductive paint
'tank' and copper wire / tube / sheet
Current controlled power supply


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## Peter Twissell (Dec 31, 2021)

First mistake / discovery:
In order to dissolve the copper sulphate into the water, the water must be warm. It's about 18 C in my house - not warm enough for the solution and most of the copper sulphate just sits in the bottom, refusing to dissolve despite much agitation.
I had mixed the solution in a plastic milk container, so I was able to simply stand it in a bucket of hot water and within a few minutes the solution was complete.


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## Basil (Dec 31, 2021)

I have only done hobby nickel plating and that was a few years ago. Fish tank accessories are good and cheap, a heater to keep the solution at the correct temperature and a small submersible circulating pump to keep the solution moving. Current settings made a big difference in finish quality, Smoothness etc. Good luck! Very interested in the outcome.


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## Peter Twissell (Dec 31, 2021)

Thanks Basil.
I have done some electroplating in the past. I have managed without heaters or circulators, simply occasionally stirring the solution manually and setting the plating tank in a dish of warm water.
This process only needs to be kept slightly above room temperature and I suspect the plating current itself may be sufficient to make up for the slight heat loss once it gets going. If not, I will top up the heat with more hot water in the dish.
I would be concerned that fish tank equipment might suffer corrosion from the acidic solution.


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## Ken I (Dec 31, 2021)

Pete, Thanks for the progress report and the link - a useful resource.

Looking good so far.....

Regards, Ken


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## Peter Twissell (Dec 31, 2021)

Plating begins!
The next little problem-ette is immediately apparent - the hollow 3D printed patterns are of course buoyant in the solution and don't want to remain immersed.
Fortunately attaching the crocodile clip to the common conductor is enough to weigh both patterns down into the solution.
Within seconds of switching on power, plating could be seen on the conductive paint adjacent to the copper conductor on both parts, indicating that the circuit is complete.


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## Ken I (Dec 31, 2021)

In a curiously related incident - I was having a foundation slab cast for a very large Chrome plating system - it had a number of PVC tubes set through it and also through the wooden box form.
As soon as the concrete pour was hit with vibrators, the buoyancy lifted the box form - concrete spilled out everywhere - dirty great mess. Ahh well.
When James Cameron filmed the sinking of the Titanic - the grand staircase also floated and proceeded to self destruct.
Boyles law cannot be bargained with.
Regards, Ken


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## Peter Twissell (Dec 31, 2021)

First failure:
After a few minutes plating, both parts had started to turn green, which is normal when viewed through the blue solution.
However, one part had started to produce large bubbles from a point approximately halfway along its length.
After switching off the current, both parts were lifted out of the solution, whereupon the one which was bubbling fell apart.
There had clearly been a leak of solution into the soluble PVA pattern, which had begun to dissolve.
Upon inspection, the other part also had a small leak, evidenced by the paint cracking at the end with the conductor wire.
I have put the second part back into the tank to continue plating, with the leaky end raised just out of the solution.

I don't expect the first attempts to produce usable parts - at this stage it is a learning exercise.


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## Peter Twissell (Dec 31, 2021)

After another 25 minutes in the tank, the second part failed, developing cracks through the plating as the PVA pattern expanded due to solution leaking in.
That's it for today. I'll get some more patterns printed and have another go.


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## Ken I (Dec 31, 2021)

Not bad for a first attempt - I haven't printed PLA only ABS and I normally "glaze" it in Acetone vapor - I once tired dunking - total failure as the porosity (and voids) in the print simply filled up with Acetone and proceeded to dissolve the part from the inside.
You are probably going to have to lacquer those parts substantially before the conductive paint layer.

Edit: Thinking about it I'd use glazed ABS and dissolve it with Acetone - at least it won't care if liquid gets inside during the plating process.

Regards, Ken


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## Peter Twissell (Dec 31, 2021)

I'll be trying some more PVA patterns with more attention to sealing with the paint.
I'll also try some PLA patterns.


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## Willyb (Jan 1, 2022)

That's not bad for your first try. It's going to take some experimenting for sure. Very interested in this process. 

Cheers
Willy


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## aka9950202 (Jan 1, 2022)

I discovered that the spray  bottles of isopryl alcohol are not damaged by acetone.  I now use  acetone  spray to complete the ABS parts I print. 


Cheers, 

Andrew in Melbourne


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## ajoeiam (Jan 1, 2022)

Peter Twissell said:


> Electroforming:
> 
> A few members have expressed an interest in this process, so I shall endeavour to describe my efforts in as much detail as possible.
> There are numerous websites which detail the process. I have been using this one: Electroforming Resources for Aspiring Artists
> ...




Please sir 

I do believe that what you have been presenting is very worthy of being a separate thread. 
that would make your process and all the other very valuable information far easier to find by anyone looking for information in the future. 
Much trickier to find when its in an engine build thread - - - at least imo. 
(Ja I 'know' it would still be findable but in its own thread - - - well isn't that a more elegant way of doing things - - yes?)


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## Peter Twissell (Jan 1, 2022)

I'm quite happy to create a separate 'how to' thread.
While I go through the development process, I'll keep posting in this thread. When I have made some successful parts, I'll write a dedicated thread with all the information in the correct order - plus a link to this thread for those who want to see the 'warts and all' trials and errors.


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## propclock (Jan 1, 2022)

"Warts and all" is the most important part . Thanks for sharing.


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## ajoeiam (Jan 2, 2022)

Peter Twissell said:


> I'm quite happy to create a separate 'how to' thread.
> While I go through the development process, I'll keep posting in this thread. When I have made some successful parts, I'll write a dedicated thread with all the information in the correct order - plus a link to this thread for those who want to see the 'warts and all' trials and errors.


Thank you for your sharing. 
I know I don't have enough years to do all the experimenting and doing that I have in mind. 
Makes it easier to get things done using the trials and tribulations of others!!!!!!!!

Regards


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## Peter Twissell (Jan 2, 2022)

While waiting for more 3D printed patterns, I spent today in the workshop making tappets and pushrods to complete the valve gear.

The tappets are of the 'bucket' type, running in a relatively large bore. They are bored out to 0.5mm wall thickness.
Pushrods are aluminium and serve to fill the gap between the bottom of the tappet bore and the end of the valve. Valve clearance will be adjusted with shims in the bottom of the tappet bore, under the pushrod end.

The first photo shows one tappet in place and another lying in the cam tunnel of one of the blocks.

The second, taken with the flash, shows the valve cap and clip installed.


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## Peter Twissell (Jan 2, 2022)

Keen eyed observers may have noticed that the tappet has an angled end face.

The tappets and valves are not parallel to the cylinders, but angled to them when viewed from the end of the engine.
This angle allows the axes of the valves and tappets to intersect the axis of the camshaft. The angle also gives improved gas flow between the combustion chamber and the ports.
In order that the LH and RH valves are correctly timed (i.e. at 180 degrees to one another), it is necessary for the tappet faces to be angled so that they are presented to the cams at 180 degrees. These angles generate a slight difference between the valve acceleration profiles, but when the valves are so small and light, the differences are negligible.

I have now assembled the engine with the valvetrain and gears in place, to check that I haven't built an engine which will run the wrong way (i.e. for a conventional prop), or indeed with one CW cylinder and one CCW cylinder!
All appears well so far and all valve events are in the correct order. With no rings on the pistons, the engine turns smoothly enough that the compression and relaxation of the valve springs are the dominant forces felt when turning the crankshaft.
I did make a short 25 second video, but it is too large to upload, so I've put it here for anyone who may be interested.


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## Peter Twissell (Jan 3, 2022)

Head gaskets will be instrumental in setting up and tuning the engine, so I expect to be making several sets in various thicknesses, possibly different materials.
To make the head gaskets, I first made a pair in 3mm thick steel, so that they could be used as patterns to make gaskets.
The initial gaskets are copper. I cut some short length of domestic 15mm plumbing pipe, cut them along their length, annealed and flattened them.
The blanks are then drilled, using the steel patterns as a guide. After deburring the holes, a single blank is clamped between the steel patterns and cut out with a sharp chisel around the outside and a round punch for the inside.
Each gasket takes just a few minutes to cut.


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## Peter Twissell (Jan 10, 2022)

Cylinder heads are relatively simple, but as with some other parts, I made more work for myself by designing them with radii which required multiple rotary table setups and a combustion chamber shape which required a fixture to angle the head at 5 degrees from the rotary table surface.


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## Ken I (Jan 10, 2022)

And then you find you need a fixture to make the tooling to make the part.
Arrrrgggghhhh !   Sympathies - been there - done that.

Regards,  Ken


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## Peter Twissell (Jan 10, 2022)

Yes - like those jobs when you find the piece of equipment you need requires attention - then the tool you need for that is broken and the tool you need to repair that is on loan to a friend etc....


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## Basil (Jan 10, 2022)

Peter Twissell said:


> Cylinder heads are relatively simple, but as with some other parts, I made more work for myself by designing them with radii which required multiple rotary table setups and a combustion chamber shape which required a fixture to angle the head at 5 degrees from the rotary table surface.


I can relate! So glad I bought a tilting rotary head now. No way I was messing with the mill head.


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## Peter Twissell (Jan 11, 2022)

Neither angling the mill head nor a tilting rotary table would not have achieved what I needed.
The combustion chamber 'floor' is a flat face, but it is set at a 5 degree angle to the gasket face. To achieve this, it was necessary to set the part at 5 degrees to the plane of the rotary table.
Fortunately, I had considered this in the design, so the centre of rotation is at the centre of the 1/4-32 glow plug hole and I made a dummy plug with a centre drilling so I could locate the part and fixture on the rotary table axis.


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## awake (Jan 11, 2022)

Clever fixturing is more than half the battle!


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## Basil (Jan 11, 2022)

Ah yes! of course Peter. What I was thinking would not have ended up flat more a section of a cone if I'm correct.


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## Majormallock (Jan 17, 2022)

Some success with Woods metal (Cerrabend) sample bend has worked out now to make 5 repeatable inlet tubes in 9/32 x 0.014 brass.  Might just prefer to try ally tubes!


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## Peter Twissell (Jan 18, 2022)

What tooling did you use to bend your tubes?
Were they bent by hand around a simple former, or did you make a roller type bender?


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## Majormallock (Jan 18, 2022)

Hi, Peter I made a roller bender with following former made specially in 9/32 dia. Just needed to take care of how I annealed the brass. First attempt putting the tube into my solid fuel workshop fire was too much


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## Peter Twissell (Jan 18, 2022)

I may still make a mandrel bender, as a backup for the electroforming option.


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## animal12 (Jan 19, 2022)

Did you have plans for the roller you built or did you find a design online ?
thanks
animal


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## Majormallock (Jan 20, 2022)

I just made it up out of stock and scrap. Design is based on those used in aerospace where I used to work. The following former should be longer ideally,  but it works if you just shuffle it along as you go


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## Peter Twissell (Jan 20, 2022)

Does the following former slide against the tube, or against the lever?
I have a similar design in mind, but with a roller on the lever to bear against the following former.


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## Majormallock (Jan 20, 2022)

Hi Peter, the former rolls around with the tube , sliding with the handle. Using a roller as you suggest would be better, especially if you were planning reuse for other tube siz3s


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## animal12 (Jan 21, 2022)

thanks
animal


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## Peter Twissell (Jan 25, 2022)

The engine is to be mounted to the aircraft firewall by its own mounting structure, which will also house the carburettor and support the exhaust silencer.


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## Majormallock (Jan 27, 2022)

Very nice mount Peter, given me some ideas to possibly use, thanks. By the way, what compression ratio do you use


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## Peter Twissell (Jan 27, 2022)

Thanks!
I'm using 8:1 compression initially, but I have designed with a 1mm thick head gasket, so I have the opportunity to adjust compression either way.


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## Majormallock (Jan 27, 2022)

Many thanks


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## Peter Twissell (Jan 30, 2022)

The silencer consists of a tube, two end caps, two exit pipes and a baffle.
The tube is machined from solid (available material) to 1mm wall thickness and drilled for the exhaust entry and exits and for the mounting screw.

The exit pipes are machined with a small shoulder. They are attached to the tube using 'Technoweld' aluminium 'brazing' rods.

The end caps are hollowed using a specially ground tool with a 1.5mm radius, to a series of calculated steps to produce a hemispherical radius inside. The outside is then finished with a radius turning attachment to give 1mm wall thickness.

The baffle is machined from 5mm thick aluminium, thinned to 2mm thickness with bosses left to be drilled and tapped M3 for the screws which retain the end caps and one which supports the silencer under the engine mount.

When assembled, the baffle divides the tube into two, so exhaust gas is forced to pass from the central inlets, along the front half of the tube, via the hollow end caps and along the back half of the tube to the outlets.


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## Peter Twissell (Jan 30, 2022)

Piston rings are made using the Trimble method.
I have made plenty of rings, so I can select the best fitting examples.
The rings are shown on the heat treating fixture, ready to go into the oven tomorrow.


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## Peter Twissell (Jan 30, 2022)

I now have some 3D printed patterns for the electroformed exhaust and intake manifolds.
I started plating on a pair printed in PLA (as distinct from the water soluble PVA I tried before).

This pair have been in the bath for 6 hours now and the plating is building nicely.
They appear green when immersed in the electrolyte, but are a pleasant soft copper orange when lifted out.

I now have the bath stood in a larger tray (cat litter tray) with an aquarium heater to keep the whole lot at 35 degrees C. The process will work at any temperature above 25C, but it's not that warm in the spare room where I am set up, so additional heating is required.

Measurement shows that the diameter of the parts has grown from 8.0mm to 8.8mm in 6 hours, so another 10 hours should be enough.


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## Peter Twissell (Jan 31, 2022)

A more thorough check of the parts being electroformed this morning revealed that the build up of plating thickness is substantially greater in areas close to the anode than it is in areas further away.

The location of yesterday's measurement was close to the anode and showed 0.65mm thickness after 10 hours.
Locations in the areas furthest from the anode show only 0.2mm thickness at the same time.

I have now turned the parts around, in an attempt to balance out the plating thickness.
I will continue the process until I have a minimum of 1mm thickness all over. I can reduce any excess thickness with emery.

Also noticeable is that locations close to the anode are of a rougher finish than locations further away.

For the next attempt, I shall arrange two or more anodes around the bath, in an effort to even out the plating rate.


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## Ken I (Jan 31, 2022)

Peter,
         Looking great thus far - learning curves are a sod.

Re previous comments on thief rings etc.
You want to have a uniform current (amperes per square inch) all over by provision of anodes and "thief" cathodes. Alas practice is invariably a compromise on theory (AKA just not possible.).

If you have areas that exceed the maximum rate, you may just produce mud, get too low and you may just produce nodules - or vice versa - confounding variables.

Moving the parts about in solution (as done for through hole PCB plating) or rotation (with obvious commutating problems - solved by just rotating backwards and forwards) or simply moving the solution about via a pump or impellor. Relative motion also helps increase deposition rates by clearing the diffusion layer away from the cathode. (A'la YRPS - Yamaha Rapid Plating System which typically deposits Nickle and Chrome at very high rates.)

Regards, Ken


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## Peter Twissell (Jan 31, 2022)

Thanks Ken,
I had considered using a fish tank pump to circulate the electrolyte, but I was concerned about introducing bubbles. I have a small pump, but even that generates a storm in my 1 litre bath! Also, I am a little worried about the effect of the electrolyte on the internals of the pump.
Ideally, I would use a magnetic stirrer.

So far, excess build up at edges appears to be trivial. In any case, I will be silver soldering flanges to the ends of the tubes, so a bit of extra wall thickness there may even be desirable.


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## methuselah1 (Jan 31, 2022)

Have you considered using an old saucepan and using the whole tank as the anode, Peter? You've got stainless steel, aluminium and copper to choose from.

Another thought is to use an automotive washer pump- 12 volts, gear type with plastic workings and low out put. Ditto for using a wiper motor to impart reciprocating motion.


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## Peter Twissell (Jan 31, 2022)

A copper tank would do the job, but it would require care to ensure that it didn't erode away through the bottom.
My anode is a piece of domestic plumbing pipe and about half of it is gone already!
Other metals in the electrolyte are a no-no.


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## Ken I (Jan 31, 2022)

Peter,
          Laboratories use a magnet in a ceramic case - driven remotely by a further motorized magnet under the beaker - maybe a lash-up ?

Correct - you don't want to entrain bubbles.

The anode is obviously sacrificial but you can use heavy gauge copper wire quite liberally - I don't recommend ever using the tank as an anode - in my experience  even accidentally making the tank the anode results in disaster - besides anything other than copper is going to ruin your electrolyte.

Regards, Ken


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## methuselah1 (Jan 31, 2022)

Ken I said:


> Peter,
> Laboratories use a magnet in a ceramic case - driven remotely by a further motorized magnet under the beaker - maybe a lash-up ?
> 
> Correct - you don't want to entrain bubbles.
> ...



Magnetic stirrers (pills or fleas in lab tech slang) are cheap enough to buy- but the hotplates with the motorised magnet generally aren't. I was looking at them the other day for  some reason. However, when I was a lab tech, I scrapped dozens of dud hotplates, (ammonium chloride kills them) but saved a fair few of the magnets, and if you want to try that method, I can get one in the post for you.

I like your end of mail quip, Ken- but its funnier if you write "I'd rather have a full bottle in front of me, instead of a full frontal lobotomy"! And try saying that after a few drams!


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## Peter Twissell (Jan 31, 2022)

Thanks for your kind offer.
I am now planning a more "professional" setup, with integrated heating and electrolyte circulation, multiple anodes and filtering to prevent debris from anodes from arriving at the cathodes.
I have in mind a peristaltic pump.


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## Ken I (Feb 1, 2022)

Peter, Amongst other research while you are looking - look up "Hull Cell"

This is a small glass plating bath with the anode and cathode at an angle to each other - giving a variable current density across its face.
It is used to determine the optimum value for your solution - or to determine on a small scale what any changes or remedial actions will have on your solution.
When you have a tank with 20000l of chromic acid (as I did) you don't make changes or additions without first testing it on a small scale.
You can obviously lash this up and use it to determine optimum current density.

I only ever pumped chromic acid with peristaltics or magnetically coupled pumps - each have their own quirks - the wierdest was the magnetically coupled did not like running without back pressure - would cavitate and fail to deliver - even with flooded suction ? I suspect that the driver and driven bar magnets accidentally worked like an induction motor with the driver bar inducing a current in the driven bar - thus repelling it into the arms of the next pole - a vicious circle resulting in a low torque speed multiplier - it simply ran away at speed if not presented with resistance creating an impenetrable cavity that not even flooded suction could penetrate ? One of the wierdest phenomena I have seen. It may have just been a quirk of the particular brand of pump - but wierd nonetheless.

Regards, Ken


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## Peter Twissell (Feb 2, 2022)

Success!
The pair of exhaust pipes came out of the bath after 33 hours looking like this.


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## awake (Feb 2, 2022)

33 hours - sounds exhausting!


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## Peter Twissell (Feb 2, 2022)

A little cleaning up with a fine file soon got the bobbly surface back to amorphous copper.

Both ends cleaned up to the desired 1mm wall thickness.
Some areas are only 0.4mm thick, which is a little thinner than I'd like, so they will go back into the bath with the anode closer to the thin areas.


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## Peter Twissell (Feb 2, 2022)

Fortunately, the process can be left to run unattended, so 33 hours is not so much of a task.


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## awake (Feb 2, 2022)

That was supposed to be a pun. Exhausting ... exhaust pipes ... yes, pretty feeble, but I do what I can.


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## Peter Twissell (Feb 2, 2022)

The pun didn't escape me.
I just decided not to pipe up about it.

I'll get my coat....


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## awake (Feb 3, 2022)

Oh ho! You do know that punsters cannot stand to be ignored. A groan is taken as a compliment. Silence ... just hurts. 

So in that vein ...



Peter Twissell said:


> I just decided not to pipe up about it.



Groan!


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## Steamchick (Feb 3, 2022)

Pipe down and get back to topic.... 
The plating thickness is not based on proximity of anode, but electric field strength - which in turn is based on shape! Which is why the inside ( where there is almost no electric field ) will be unplated.  The Rough surface bobbling you experienced is also a field-strength issue. As soon as the deposit of new copper starts to get even microns uneven, the election field strengthens locally where there are peaks, so builds more rapidly there than in the troughs. The way to build any coating thickness electolytically, is to stop every hour or so and polish the surface level again. (Use very fine wet n dry paper?). Just like paint film building.
Enjoy - and we'll done so far.
Just an odd question... why copper plate the exhausts? Will you nickel plate, then chrome on top? If so, why do you need such a thick plating? If you intend just polishing the copper, it will colour and burn black oxide, depending on how hot it gets. I have discoloured copper pipes from my boilers with the temperature of super-heated steam.... not as hot as your exhaust gases?
Now I am hot, exhausted, and too blown way for more comments...
K2


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## Peter Twissell (Feb 3, 2022)

Hi Ken,
Thanks for the tips.
It was my understanding that anode proximity had a direct effect on current per unit area and therefore deposition rate.
My exhausts are not copper plated, they are copper!
The part I am plating onto is a sacrificial 3D print, which will be dissolved out later.
I will nickel plate the pipes after I have silver soldered the flanges on.


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## Steamchick (Feb 3, 2022)

Thanks Peter. That clarifies your need for more wall thickness. 
K2


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## Steamchick (Feb 3, 2022)

I am a bit surprised you can't bend pipes from copper tube?
K2


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## Steamchick (Feb 3, 2022)

Peter Twissell said:


> Hi Ken,
> It was my understanding that anode proximity had a direct effect on current per unit area and therefore deposition rate.
> My exhausts are not copper plated, they are copper!


I guess that if you use a small anode, close to the zone you want plating, the locally the electric field will be a bit stronger. It relies on the inverse square law. But most plating keeps the anode further away to try and obtain a more uniform field. I'm sure you are using CAD for the component design, so load-up an electric field programme to look at your proper anode shape and placement.
K2


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## Peter Twissell (Feb 3, 2022)

Yes, I could have bent the exhausts as the radii are not too tight.
The intake manifold has tighter bends (1D) and some of the bends are very close together.
I decided to electroform the simpler exhausts first, as a practise before embarking on the more complex intake manifold.


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## Ken I (Feb 3, 2022)

Now you can let your imagination run riot in 3D and translate it into reality.

A very cool project in and of itself - thanks for the tutorial.

Regards, Ken


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## Peter Twissell (Feb 3, 2022)

Indeed so, I can see applications for this process to model a variety of parts.
Cast intake and exhaust manifolds for a start, but also any part which would be pressed steel on a full size engine, such as sumps, timing covers, rocker boxes etc.
A radiator would be ideally suited to electroforming.
Essentially, any part which requires a reasonably consistent wall thickness.
As I mentioned earlier in this thread, once I have developed the process, I will write a "how to" article.


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## Ken I (Feb 3, 2022)

Pete, I clearly never thought it through - sumps and diff cover etc. would be a nightmare to machine from solid - by this method you can create parts that will confound most onlookers - go for it - add draw marks and wrinkles to your model.
You can also scan and scale the real thing - lots of scope here.

Regards, Ken


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## Steamchick (Feb 4, 2022)

Peter, you make me feel like I live in a 2-dimensional world and you live in 3d! But I'm happy and feel comfortable with my paper and drawing board. (For now). Good luck building a more uniform thickness on these shaped components. Please note: Modern cars are now using "stable plastics" for intake manifolds, so you can follow that idea, but for exhaust manifolds, I think you have good ideas! But watch out for thin sections where the electric field is weak. (Inside every curve). You'll need to make anodes to go in the middle of those curves to get some electric field to deposit the metal. 
I think (never having done plating) that the theory says you can use any conductor for the anode, as the solution holds the ions of depositing material. So as long as some part of the anode is of the material to be deposited (of similar area or greater, than the depositing area) you can use parent metal or "other metal" (Stainless steel? Aluminium?) to make electric fields where there are otherwise none. 
 In your case, I think some anodes in the middle of any curved surfaces should work to keep the field where you want it.
Best if you get an electric field modelling software for the CAD system you use for modelling the parts. Then you can "teach yourself" where to put anodes to make the electric field more uniform around the component to be plated.
Working in the car industry, I always though it to be very clever how they manage to chrome plate onto plastic handles.... - by making the surface of the plastic conductive!
K2


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## Peter Twissell (Feb 20, 2022)

The exhaust pipes were reasonably successful. After cleaning up, there is sufficient thickness of copper all over, but there are a number of pits and grooves in the surface. These will need filled with silver solder when I attach the end flanges, then the assembly will be nickel plated.
Yesterday I started plating the more complex induction manifold.
I made a shaped anode, in an attempt to even out the plating thickness.
After about 20 hours, the part looked like an octopus tentacle, with extensive "bobbles" over most of the surface.
I tried to file the bobbles down, to get back to a smooth surface, but found that the smooth plating was very thin and came away from the pattern.
I have now peeled all the plating off and I will start again.
I suspect the bobbling may be either due to the close proximity of the anode, or die to the anode being too large.


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## Steamchick (Feb 20, 2022)

Hi Peter, not being an electroplating expert, I can only guess.... the electric field is too large? Drop the voltage...? Increase the gap to anode? It should be a 1/r-squared relationship (inverse square law). If you want to be technical. But surface radius (locally) increases the local field dramatically, so when you get a tiny crumb (dust size) of plating at some point, the electric field has instantly become bigger (a very small radius has appeared,, compared to the flat surface!) and encourages more plating at that point. Hence the bobbles! Stop after a tenth of the time, flat the slightly bobbled surface, then continue.
Or get an electric field programme and add your CAD models.
But really, I have no idea, except for the physics I remember.
K2
But maybe you need


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## Peter Twissell (Feb 20, 2022)

Hi Ken,
Yes, I think you're right about the inverse square law and growth of bobbles.
I don't think there's anything I can do about the inside radii on the part. I've already established that the anode can't be too close to the part. With the anode away from the part, there is no way to increase the field at the inside radii.
That said, the difference didn't seem too bad on the exhaust pipes.


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## Steamchick (Feb 20, 2022)

I was referring to the micro-radius of particles, rather than the macro radius of the tube diamer, or bend radius.
K2


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## Peter Twissell (Feb 20, 2022)

Indeed so.
With the anode close to the part, the effect of the micro radii on the bobbles is amplified. So the anode must be further from the part, which precludes doing anything about the macro radii.


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## Ken I (Feb 21, 2022)

Pete, yes those "bobbles" are because of too high a current density - which is caused by the anode being too close (inverse square rule). This leads to preferential growth points where the point current density is higher - a vicious circle.
The inverse square rule plays havoc when trying to get even distribution on complex parts - hence a mixture of anodes and thieves are used - but its something of a black art.
There are also chemical agents which work against over-current - I don't know what they are or how they work - but are used in solutions normally termed "self-leveling".
https://www.pfonline.com/articles/m...of-leveling-in-decorative-acid-copper-plating
Specifically "Self Levelling Copper" - typically used as the "undercoat" for Nickle & Chrome decorative finishes.




Image from the link above....
I mentioned a Hull Cell earlier - I suggest a trial flat part at an angle to a flat anode to determine the optimum current density for your solution.
I'll leave the math's to you - sum of inverse squares x dx = total amps - you can use calculus or a spreadsheet approximation via discrete "strips".
Then you can determine from the sum area of your components and thieves, how many amps you should be plating at.

Regards, Ken


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## Steamchick (Feb 21, 2022)

Thanks Ken 1. I love to learn about something new! - Like this!
K2


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## Peter Twissell (Feb 21, 2022)

Hi Ken1,

I've looked into levelling additives and I understand the mechanism, but the additives are not easily available and the process requires reversing the current direction to erode high spots away. This is beyond the level of complexity that I intend to invest.

In the meantime, I've made a Hull Cell, using a piece of plastic painted with graphite paint as the cathode to minimise the variables between the cell test and my part. I'll run the test as soon as the paint dries.


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## Peter Twissell (Feb 24, 2022)

So I made a Hull cell and ran the test.
The cell is made from plastic and the cathode painted with graphite paint, so as to be representative of the part I want to plate.
From an online source, the test should be run for 5 minutes at 1 amp.
The photo shows the cell in the plating bath after 5 minutes. Plating had begun to deposit, spreading evenly from the location of connection.
Interestingly, a thick layer of plating developed quickly on the copper wire connection.
I left the cell to continue playing for a total of an hour, in the expectation that it might produce some more useful results.
The third picture shows the plated cathode.
There is some unevenness, but mostly around the connection point.
Certainly no clear distinction between the end closest to and furthest from the anode.


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## Ken I (Feb 25, 2022)

Unusual result ? I suspect your (relatively) heavy copper connector was running interference.
As far as I know you should connect both anode and cathode at the wide end to minimize this.
The current needs to be high enough to induce bad plating at the narrow end. 1 A for what looks like about 2 square inches would be a bit low.
If I was running this test - I would (from the first test) take a stab at the current density - recalculate and run the test again.
I think I would also run the plate parallel for a while to develop an even layer over the conductive paint first - I suspect the  paint is unable to distribute the total current well (initially) resulting in high current density about the connector simply because of losses in the resistive paint over distance.
Regards, Ken


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## Peter Twissell (Feb 26, 2022)

Second attempt with the Hull cell, cathode stripped and repainted with graphite, connections moved to furthest ends, current increased.
5 minutes at 1 amp to cover entire surface of cathode with a layer of plating.
1 hour at 2 amps.
Evidence of "burning" (excess current) at the end closest to the anode, but otherwise the plating conforms to the brush marks from painting.
This was at several times the current density I was using for the part, so the burning was expected.
If I have learned anything from this, it is that I could be plating at higher current density (amps per square inch).
I am happy to stick with the current density I was using (0.1 amp per square inch).
I've now started another attempt at the part, but with the anode well separated from the cathode.


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## Peter Twissell (Mar 5, 2022)

Finally some success with the intake manifold!
This one was run at just 0.2A, a fifth of the current which worked for the exhausts.
At the start of the process, even with the low current, some bobbles were beginning to appear on the areas closest to the anode.
I used the Hull cell parts to improvise a baffle between the anode and cathode, which appears to have worked, giving a more evenly distributed field at the cathode.
The part took most of the week to build, around 120 hours.
I think the lesson here is in the field distribution.
Ideally, I think the bath should have been much bigger, so that the size of the part is small by comparison with the distance to the anode.


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## Peter Twissell (Mar 7, 2022)

A bit of cleaning up and melting out the pattern and the result is a useable part.
Note that the wall thickness is uneven at the small ends, where there are tight radii and high field density at the extremities of the part.
For this application, this is not a problem.


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## Peter Twissell (Mar 14, 2022)

The electroformed manifold parts are soldered together, using a fixture to locate all the points of attachment to the engine.
The solder is a high melting point alloy which came with a boiler kit.


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## Peter Twissell (Mar 14, 2022)

Manifold fitted to the engine.
Now to dismantle, fit the rings, set timing, reassemble and run...


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## Peter Twissell (Apr 4, 2022)

The engine ran for the first time on Saturday morning.
And I broke it after just a few seconds.
Nothing serious, the timing gears were contacting the inside of the timing gear cover and generated enough aluminium debris the jam the gears.
I shall make a new cover with more clearance. I wanted to make a new cover anyway, with an oil drain / crankcase breather feature.
I had to make my own glow plug driver.
I had read that the common glow drivers which use a 12V source should drive two plugs in series, as they are current control devices.
My normal driver won't do it.
Fortunately, among my collection of electronics, i have a couple of boost/buck modules which can be configured to operate as current control.
This allows me to set a current and the device will compensate for variables such as long leads and keep the plugs glowing nicely.


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## Arild (Apr 5, 2022)

Peter Twissell said:


> The exhaust pipes were reasonably successful. After cleaning up, there is sufficient thickness of copper all over, but there are a number of pits and grooves in the surface. These will need filled with silver solder when I attach the end flanges, then the assembly will be nickel plated.
> Yesterday I started plating the more complex induction manifold.
> I made a shaped anode, in an attempt to even out the plating thickness.
> After about 20 hours, the part looked like an octopus tentacle, with extensive "bobbles" over most of the surface.
> ...


It looks likes arms from a starfish!


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## Steamchick (Apr 5, 2022)

Brilliant work Peter. You have also shown us how much "time and perseverance" can achieve!
K2


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## Peter Twissell (Apr 5, 2022)

Really?
I would like to have the time (and patience) for a lot more perseverance!
To my mind, this has been a fairly rapid design and build.


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## Peter Twissell (Apr 30, 2022)

The engine has run again.
With a new timing cover, with clearance for the gears, it fired up easily and ran at about 1/4 throttle with the first guess needle setting.
The engine was turning a 12 X 4 prop, which I had guessed on the basis that it is likely to achieve power comparable with commercial 10cc four strokes.
When all seemed well after a couple of minutes running, I ventured to open the throttle to about half way.
This resulted in a rapid increase in rpm, followed by slowing quickly to a stop and feeling very stiff to turn.
Back on the bench and dismantled, I have broken the crankshaft.
So, back to the CAD to design a more robust crank.
On the plus side, the engine appears to be developing more power than expected.
I could probably reduce the compression a bit and make another crank to the original design, but I've tasted the power now!


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## Steamchick (Apr 30, 2022)

Hi Peter,
From experience with crank design for High Voltage Power circuit breakers (single shot, but highly stressed! Max 120 g acceleration of the piston!), the most significant design improvement was to maximise the radius at the end of crank journals and main-shaft journals. A change from 1mm to 3mm in corner radius achieved in excess of 5000 operations instead of less than 20.... Just what we needed!
Check all the stress raisers, (sharp corners) and look-up stress concentration factors for shaft diameters and corner radii.... You'll soon work it out.
K2


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## Steamchick (Apr 30, 2022)

Hi Peter, Just found the crank in Post #36. I was looking for the crank journal and main diameters... It looks like you have 10mmdia mains, for the bearings. But I was unable to find the crank pin diameter?
I have the book on building the Maltese Falcon - 260cc flat four engine:
Mains: 25mm dia,
Big-Ends: 0.660".
I am not sure how this relates to your engine, but may give you some idea of the design "balance" between components. The corner radius on journals is 1mm (0.040"). Not bad for stress reduction. maybe ~1.8? on the main bearing journal. Of course, your crank pins are not so easily calculated with being pressed pins, but which failed? Main or crank-pin?
K2


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## Peter Twissell (Apr 30, 2022)

Thanks Ken.
My crank is a pressed assembly, because my rods are one piece.
The big end pins are 6mm hard dowels, pressed in to the crank webs and secured with a spot of Tig welding.
The welds failed, allowing the crank to twist.
I will make a new crank with more interference in the press fits. I was a bit over cautious with the fits at the first go, concerned about distorting the webs.
I will also add a weld prep so I can get more penetration.
I don't have space to make anything bigger, so I have to make the best of the original design.


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## Vietti (Apr 30, 2022)

You are obviously a very accomplished builder, but just a thought, when I make built up cranks I put a deep chamfer in the web and a big taper on ends of the crank pin then either mig weld or silver solder.   The deep resulting depression allows a generous weld, cleaned up with an end mill.  I usually put in a pin but drilling a dowell pin might be tough.

I mig welded my last crank pin, drill rod, so I could put a needle bearing on the con rod journal.  Did this because silver solder would heat up the bearing too much.  Pinned also.  So far working OK and I like the free spinning on a hit and miss.

John


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## Peter Twissell (Apr 30, 2022)

Thanks John,
I am always happy to hear how others have done things.
I would be a fool if I thought I knew how to do everything.
I think you have described what I am intending to do with the weld prep.
I will Tig weld it, because I feel I have more control of the heat and filler than with MIG.


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## Steamchick (Apr 30, 2022)

I understand - and think you know your job better than I! Thanks for the further explanation. I now appreciate why you avoided silver soldering. (Which is how I make cranks for steam engines with split bigends.). I don't know the calculations for the stress in the crank web when the interference  fitted pin is pressed home, but I would simply use my old book of "standard fits". Maybe the calculations would be "hoop stress" plus a stress concentration factor? Then stress added for the pin loading at max revs and bmep on the piston?
Have fun with the numbers!
K2


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## Peter Twissell (Apr 30, 2022)

Hi Ken,
Standard fits are applicable when the bore is in a relatively large section of material. My crank webs are of irregular section, so I calculate on the basis that the thick bits are essentially rigid and all the strain occurs in the thin sections.
This is, of course, an approximation, so I shall make a few test samples so I can measure strain and adjust the fit so as to maximise interference while avoiding yield in the thinnest sections.


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## Steamchick (Apr 30, 2022)

Sensible. Thanks Peter. I would have calculated the hoop stress based on the thinnest section, but with a pre-stress equivalent to twice the expansion required by the interference fit. But I am just an amateur, and I don't have the detail shape and dimensions of your webs. 
I'm pretty sure what you plan will work. Thanks for your time.
K2


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## Steamchick (May 1, 2022)

Hi Again Peter, Strange what I dream about... But this morning I had a thought. Perhaps the TIG is "heat affecting" the material, either to some embrittlement that caused the failure, or to annealing the material - thus relaxing any interference? So does the finished assembled crank effectively need re-normalising and tempering? - NOT so practical with the races built in from the attached rods.
BUT perhaps in 2 stages: As there will be (on each crank pin) and highly stressed side and a less stressed side, is is possible to partly build the crank (without rods) and (say) Silver solder the pins on one side only? Then (on the "less stressed" side) after assembly and alignment secure the pressed pin with some anti-rotation means - such as a pin - as a key? It need not go all the way through the web, I would guess half to 2/3rds depth? - Drilled after assembly and trueing of the assembly? I have even heard of a threaded pin/bolt being used as such a key-pin, as it is easier to remove for service.
Such stupidity disturbs my sleep.
K2


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## Peter Twissell (May 2, 2022)

Hi Ken,
My timing gears are pinned exactly as you show, but the crankpins are hard dowels and drilling is not practical.
The TIG weld was only a tack on the ends of the dowel, at their least stressed location.
It was the weld itself which failed, so my proposal is to add as much material as practical to the crank webs around the dowels, increase the interference fit and add a prep for a more substantial weld.


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## awake (May 2, 2022)

Peter Twissell said:


> Hi Ken,
> My timing gears are pinned exactly as you show, but the crankpins are hard dowels and drilling is not practical.
> The TIG weld was only a tack on the ends of the dowel, at their least stressed location.
> It was the weld itself which failed, so my proposal is to add as much material as practical to the crank webs around the dowels, increase the interference fit and add a prep for a more substantial weld.


Are you taking any measures to reduce the cracking that comes with welding hardened steel?


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## Peter Twissell (May 2, 2022)

Hi Awake,
I'm short, no.
I am using the weld to lock the dowel pins against rotation to prevent the assembly from twisting.
The primary strength of the assembly should be in the interference fits, so the weld should only be loaded in torsion, which spreads stress around the entire circumference of the weld in shear.


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## awake (May 2, 2022)

I should have noted that I was asking out of a desire to learn - I have done a fair bit of welding as a hobbyist, but have never attempted to weld anything hardened. At least, not unless you count TIG brazing cast iron ...


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## Peter Twissell (May 2, 2022)

I will also be learning!
I'll report how I get on with test parts.


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## Peter Twissell (Jun 2, 2022)

The new crank went together without problems. I increased the press fit of the big end dowels to the point of yield in the webs (which are made from EN24T!). Welding brought the area up to red heat, so some of the stress will have relieved. The connecting rods were clamped in aluminium heat sinks during welding and the operation performed as quickly as possible to minimise heat transfer.
With the engine back together and a 12x10 prop purchased, I have now run it for several short bursts of a minute or so mostly at low throttle settings.
It responds well to the throttle up to around half open, then there is no change in rpm at higher settings. I suspect the carb is too big.


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## mdanna (Jun 3, 2022)

HI!

Excellent job!
Watching the video of the engine running, I noticed that you used a glow pug starter to light two glow plugs.
How did you electrically connect it?


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## Peter Twissell (Jun 3, 2022)

Thanks! The two plugs are electrically in series.
I have made my own driver which supplies a constant current, so it works with one or two plugs in series.


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## mdanna (Jun 3, 2022)

Hi!

Thank you!


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