# Another Comber / Coomber build



## arnoldb (Oct 23, 2011)

I mentioned in my tooling log that I'll be starting another "Elmer" build. Besides all the Elmer engines that I still want to build, two needs immediate attention.

The Kimble engine has been nagging at me for a long time; it WANTS to be built, and I will build that one soon, but once again it's on the back-burner...

Last year at some point, I was in three minds about which engine to build next for my own collection, and after I showed my sister the pictures, she chose the Elmer #46, which I then built. When I asked her what she wanted for her birthday a couple of months ago, she said I owed her a #46 :big:. Mine is a good runner, and I can just give her this engine, but it does not quite run on breath power, so I thought it better to make her a new one, that will easily run on breath power and with a bit of added personalization. I hope this new build will do the job 

So the rules are "simple" - build a personalized, breath powered, Coomber :big: - I think I'm a sucker for punishment :big:

On to the nitty gritty then...

I'll be building mostly to Elmer's plans except for:
a) Increased cylinder bore size. An increased piston diameter will reduce the pressure needed to power through a stroke. Increasing the bore diameter means increasing the cylinder block dimensions; that means recalculating the bearing block spacings. I'll do that as I go.
b) A flywheel that is fairly light, yet with good rim mass. Light to keep bearing friction down, and outside rim mass will help it keep up rotational momentum.
c) Minimise friction... My existing Comber has quite a bit of friction in the bearings, and some "slapping" on the cam ring. For this build, I'll add a cast-iron insert on the main/port bearing; the brass running in CI compared to brass in aluminium should be an improvement. For the "slapping", well, I'll just to add a bit more clearance to the forks, make the rollers smoother, and make the cam dead-on smooth. I could add a roller bearing on the non-port bearing block, but maybe a CI insert will do that job as well.
d) Metric - all bits are converted to metric; I don't mind working in inches and fractions and thous, but pretty much everything I have access to is in metric, so I machine in metric.

I started off the cylinder block with a bit of 25 x 25 x 40mm brass stock flycut down to get it square:





That's the beginnings of the cylinder block.

A bit of marking out - to find the center on both of the long-end faces: with two reference sides marked





In the 4-jaw chuck on the lathe - finding center with a dead center... I REALLY need to make a proper pump center :big::





That was then center drilled, reversed in the chuck, and the other end's center found the same way, and drilled 7mm to fit a bit of 7mm round brass I have in stock:





That 7mm brass bar was a fairly tight fit, but as I wanted to silver solder it in there, it needed a bit of clearance for the solder to wick in, so I filed the end of the bar down a bit in the lathe to make it about 0.1mm under-sized, and then knurled the end:





The knurling raises the effective thickness of the brass bar, making it need a good whack to go into the hole in the cylinder block, retaining it fairly straight and square in the hole. It also leaves grooves for the solder to flow (wick) into the joint. I coated the hole inside the cylinder and the knurled bit with silver solder flux paste before whacking together and added a ring of silver solder and additional flux. A bit of "colouring in" with a graphite pencil around that lot followed; the penciled area will prevent flux and silver solder sticking:





Then I showed that lot my Sievert torch - LOTS of heat concentrated on the bottom of the cylinder block to make it glow dull red, took a bit longer than I'm used to; about 50 seconds for the flux to flow (it goes from looking like bubbly sherbet, to white crystals, then like burnt and black caramel, then suddenly like water all over the place) and 10 more for the silver solder to wick in properly, but it came together:




Heat at the bottom of the cylinder, as that draws (wicks) the solder INTO the joint; if you just heat the outside and top, the solder will melt, but not penetrate into the joint.

After a pickle in citric acid for the part while I had a bite to eat (~ 30 minutes) I chucked up the 7mm end in the collet chuck on the lathe, and with the tailstock support in the previously-drilled center, I turned down the end to 12mm with a 14mm shoulder:





Flipped in the chuck, and clamping down on the 12mm bit, I VERY carefully turned down the 7mm round bit to 6mm. It has a fair bit of overhang, so a sharp HSS toolbit is the order of the day:





Then I set up that lot in the mill, using a dial test indicator (DTI) to check for squareness. Obviously, the mill needs to be in near-perfect tram for this and the following machining steps:





Then I drilled and bored out the cylinder with a couple of successive drill sizes -3mm, 7mm, 13mm and then the boring head to take it up to 16mm. A blurry action photo; as the boring head was running nicely balanced, this shot is at about 800 RPM, and very fuzzy as I was paying more attention to the feed than the camera :big::





I checked for the final 16mm bore size with a telescoping gauge:




Well, not entirely true... :big: - the sizes measured are all OK, but I know that that digi caliper of mine is inclined to measure 0.05mm under size... - so that hole is actually 15.95mm :big:

I ended up with this lot for today's work:




If you click on the last photo and have look down the left side of the non-perfect bore, you'll see the slight oval where the shaft joined the body; at least the silver solder job went exactly as planned 

I wanted to be a bit further along today, but a neighbour popped in with a a gift and his young 'uns in tow. The gift is a very drinkable bottle of Scotch in return for fixing his wife's treadmill last weekend, and the young 'uns wanted to see some of my engines running. It's just as much fun as machining - if not more so - showing off my simple engines to a four and six year old... They seem to like the Elbow engine , the Comber, and of course the half-finished Cracker... pft pft pft ;D

Kind regards, Arnold


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## lazylathe (Oct 23, 2011)

Off to another great start Arnold!!!

I missed your previous build of this engine, so i will be following this one carefully!!

Andrew

Oh and how do i place my request for an engine??
My Birthday is in August so you have some time! :big: ;D :big:


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## ShedBoy (Oct 24, 2011)

Nice work Arnold! I totally understand when you say some engines must be built. I will be following along.
Brock


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## Foozer (Oct 24, 2011)

Will be watching, Hmm? a winter project coming up. Seeing the one you built earlier, tis a cutie she is.


Robert


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## arnoldb (Oct 25, 2011)

Thanks Andrew, Brock & Robert 

Andrew, I also have my birthday in August... And I like giving myself presents, so I guess you're out of luck :big:. But one never knows what might happen if you come and visit Namibia  I think my previous build of this engine is my engine build with the most scrapped parts :-[ - I hope this time it will go better though.

Robert, have you bought a mill yet ? - would make things a bit easier. Having said that though, I think it is entirely doable on the lathe. The biggest problem will be the cam profile, but if you follow Elmer's method that should not be a problem. 

Had an hour and a half in the shop after work today 

Layed out for the ports on the cylinder block:





As I made the cylinder dimensions bigger than on the plan, I left enough meat to drill the passages square rather than at the angles as on the original plans. I also increased the passage bore to 2mm from the original 1.6mm. Drilling the first passage:





Flipped the block and drilled the second passage, then milled out clearance 2mm deep into the cylinder bore:





While I had the milling cutter set up, I milled the port slots on the main axle as well:





The connection ports followed; I used a "wiggle wire" to feel for break-through into the steam passage:





Cleaned things up a bit and stopped for today. Time really flies when one is having fun! :





Regards, Arnold


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## lazylathe (Oct 26, 2011)

Looks like that vise stop is coming in very useful already!!
I like the idea of setting it up and just flipping the part and carrying on!
Saves a lot in set up times!

Great looking cylinder block!

Andrew


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## arnoldb (Oct 29, 2011)

Thanks Andrew  - Yes, the vise stop is really handy; it saves a lot of time !

Today's bit; I wanted to have more done by now, but time has a way of running out...

I started on the cylinder heads; some 25mm square Aluminium bar clocked up relatively on center in the 4-jaw chuck:




Remember, when centering up square stock, make sure you have enough travel on the dial indicator to clear the edges, and manually push in the tumbler when rotating the stock 

Faced off - I like it when I get a near-mirror finish like this:





Then some more taken off to leave a 0.5mm thick step.




The step is a nice push fit in the cylinder bore to keep the head concentric, and one needs a nice sharp point on the toolbit to prevent rounding in the corner, otherwise the head will not sit flat against the cylinder face.

The workpiece was then center drilled with a 1mm center drill, and drilled about 8mm deep with a sharp 2mm drill that I know does not drill over size. This hole should actually have been reamed to about 2.02mm, but I don't have a 2mm reamer, so I'll lap the hole out later. I just made a point of retracting the drill bit slowly from the hole; a sharp drill can leave a fairly good finish in the hole if this is done.

Then I used the parting tool (after a quick hone on it) to remove a fair bit of material on the other side:




Just a couple of straight-in parting cuts to the same depth; have I mentioned how much fun parting plunge cuts can be through the square section? :

The other cylinder head followed, using the same method. The one on the left shows the face that points into the cylinder, and the gory one on the right what it looked like after the parting off on the other side. Not quite as bad as it looks; it's got some cutting oil stains on it as well:





To clean up the messy face, I just chucked up a bit of 2mm rod in the collet chuck, leaving a short length protruding to engage the holes in the cylinder heads, and took a bit of carton and stuck it over that:





Then I used the revolving center in the tailstock to tightly press the cylinder head to the front of the chuck, and with light cuts turned the face and boss to final sizes:





To clean up the face of the boss was another matter; one cannot get close enough without damaging the center; something I REALLY do not want to do. So I moved away the tailstock, and with a narrow strip of emery pressed against the face with the forefinger of my right hand, I started the lathe; the pressure keeps the cylinder head engaged against the collet chuck, and because the contact area against the paper is larger than that of the emery on the face, there's sufficient drive to finish it. NOT the best way to do things; it would be better to stick the cylinder head to a mandrel (with superglue or double sided tape) or clock it up in the 4-jaw against a backstop to finish machining.

A piece of 2mm rod passes easily yet closely through both holes with very little binding. A Little lapping will sort the binding out in just minutes:





Next I set up to drill for the cylinder mounting screws. I marked one side of the cylinder out just for visual reference, then found the left back edge of the cylinder block, dialled in the location of the first hole, and set the X and Y dials to 0. A quick check locating the other hole locations on the handwheels turned out well:





Then I clamped one cylinder head to the block and drilled the four 1.6mm holes needed to tap for M2.




I really need to invest in some spotting drills... I'm still using a center drill to spot the holes before drilling.
Flipped the block, and did the same on the other side using the other cylinder head clamped down.

On to tapping the holes in the block. For tapping M2, I use the cruddy-looking tapping handle and tapping guide shown:




I'm a big old wimp - When I get around to tapping holes in a cylinder block, I religiously follow through the holes with each tap in the set; cleaning the tap after each hole. It may take much longer, but after having put a lot of time, material and effort into the cylinder block, the last thing I want is to have it ruined by breaking a tap in it!

One thing I have found to be really convenient is to use a countersink to lightly countersink around each hole before tapping. I just do it by twirling the countersink between fingers until there's a spot just slightly larger in diameter than the thread size:




This serves multiple purposes. On a cylinder face, it prevents tapping from raising a burr above the level of the face, keeping it nice and flat. It also seems to help to make the tap start easier into the hole. And last, the tangent surface of the countersink reflects some light when looking through the hole of the tapping guide, making it easier to locate over the hole.

For this engine, I'm going to use 2mm countersink screws to retain the cylinder heads. I just clamped each cylinder head in a loose vise, and on the drill press drilled the holes out to 2mm clearance and then countersunk them, using the drill press depth stop to limit depth:





I also milled each cylinder head down to final size on the square ends, and ended up with this:





Next I need to start laying out the base. As I'd increased the cylinder dimensions, the bearing posts need to be relocated from the original plans. To get a feel of what things would look like, I compared the cylinder block to my existing Coomber's:





I think it will look OK - just a bit chunky maybe, because it's fatter. But I didn't expect one thing...  :wall: :wall: The new cylinder was meant to be the same length as the original with the same stroke... It's about 3mm longer! - had a look at the plans, and the fuzzy dimension on the printout says it all... The cylinder block was supposed to be 13/16" long, but on the printout it looks like 15/16" and that's what I made it, so it's 1/8" too long... That means I'll have to increase the size of the cam - the original is already very close in clearance and there's no way I can keep to the original cam size now. Seeing as I have 1/8" more stroke available, I might as well adjust the cam for that as well.
I guess my sister's going to get a bigger engine than I thought :big:

Regards, Arnold


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## arnoldb (Oct 30, 2011)

A good night's rest makes things look better 

This morning I re-calculated the dimensions for the cam ring to use the new piston stroke, and added a bit of extra clearance to the connecting rod length in the process. The original dimensions would not have enough clearance on the center height of the bearings, so I had to compensate for that as well... So, one wrong-size cylinder and the original changes to the base are still needed as expected, but the bearing columns had to get the once-over as well. This lot took a surprising amount of time to re-design so that things would (hopefully!) work out.

A fairly quick C-o-C later to put all the new dimensions on one bit of paper:




 :big: It's not pretty, but it makes sense to me...

A rummage around, and some bandsawing, and I had bits of stock to start with:





After some work on the mill with the fly-cutter and end mills, I had those to size and ready for lay-out. The bearing blocks were super glued together early on to allow me to machine them as a pair to maintain a semblance of accuracy:





I nearly stopped for the day at that point, but decided to drill and bore the bearing blocks to 16mm to accept bushes:





Then I did stop for the day:





Not a lot of progress, but things might pick up in the evenings 

Regards, Arnold


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## lazylathe (Oct 30, 2011)

A lot of progress Arnold!!! ;D
Good catch with the bigger cylinder bock! That would have been a bugger to catch later on in the build.

Coming along very nicely!!!

Andrew


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## bearcar1 (Oct 30, 2011)

Hi Arnold,

You always seem to make it look so effortless. As usual, well thought out and neat. Your sister will (should) be delighted and thanks for having us along for the ride. 

BC1
Jim


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## ShedBoy (Oct 30, 2011)

Nice to see some hand drawn plans, makes me feel better as I was thinking everyone was a CAD expert. That cylinder looks great.
Brock


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## arnoldb (Nov 1, 2011)

Thanks Andrew  Yes, Fortunately I caught it; otherwise I would have had to re-make the columns :-\

Hi Jim ;D - Thanks! - it looks like the ride might be a bit bumpy, so hang on :big:. "Effortless" Rof} - I wish ! - but it's a LOAD of FUN ;D

Brock, thanks  It's just a lot quicker for me to draw what's in my head by hand; I use CAD when I need it but I'm no expert with that!

Stole two hours in the shop after work today 

I used an old "incorrectly made" needle valve stem to find the location for the first mounting hole to drill in the columns and zeroed the X and Y dials on it:





Then I started drilling the holes, just by feeding in the coordinates on the mill. The third hole was a bit of a disaster; the 1mm center drill I was using to spot the hole location before drilling snapped it's tip in the hole:





I used the sharp side edge of a pair of needle-nosed pliers to grab on to it and gently tried to reverse it out of the hole. A bit more snapped off, and after poking around in the hole with a sharp scriber I could feel there was a bit left. Out of sheer desperation, I plunged the snapped center drill in rapidly, hoping that it would deflect and then pick up and extract the bit of HSS trapped in the hole together with the swarf:





 It worked; after that plunge, scratching around in the hole with the scriber I couldn't feel any hard bits in there, so I drilled the hole to size without any further fiasco, and the last hole went well as well:





Tapping the holes went well; in the background you can see the bottle with the purple-coloured methylated spirits I use for tapping aluminium:





I wasn't in the mood to set up the rotary table to round over the tops of the bearing columns, so I used a 16mm drill bit's shank to support the columns and started milling away facets - a quick job, but just make sure there's no swarf trapped below the drill bit (or supporting rod):





This is what the columns looked like fresh off the mill; the glue holding them together came loose in the process, but fortunately they need not be held together any more at this point:





Getting rid of the facets is easy - a couple of light strokes (literally about 10) with a sharp file around the outside, and you can see the difference:





A quick rub over emery, and that's where I stopped for the day; there's still some tool marks left, but I'll remove those later, as I need to do a bit more work on the one column and also press in the bearings once made:





Regards, Arnold


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## arnoldb (Nov 5, 2011)

This afternoon I had a good solid 4 1/2 hours of shop time 

Started off on the base, and poked in the mounting holes for the columns:





I needed to mill a 2mm wide slot 6mm deep - and re-cutting chips is a problem, so I used a bit of wire to pipe in air from the compressor:





That slot would need 10 passes at 0.6mm deep per pass, so I dragged a chair closer and got comfortable. The first pass nearly done:





And a little while later, all done without any drama:





Then I flipped the base, and countersunk the column mounting holes, and also drilled two 3.3mm holes 10mm deep to tap M4 for the mounting the base to wood later:





A trip to the bandsaw, and I got rid of some excess from the base:





And milled the rest down to size:





I thought I was done, then remembered I still needed holes to mount the cam to - those followed in short order - 2.5mm to tap M3:





When it came to tapping the holes, a problem raised its head - my taps are too short:





That's not the first time I've had this kind of problem with my M3 taps... So I diverted a bit and made a quickie tapping handle for such cases:





It works a treat ;D - I just have to shorten the grub screw a bit:





I was thinking of making cast-iron bushes to press into the columns - to give good bearing properties combined with the brass that the cylinder block and shafts are made of. Unfortunately I could not find any in a suitable size, and while I do have some 25mm CI I could turn down, that seems a bit of a waste for such an expensive commodity... My next best choice was phosphor bronze, which I have quite a bit of and can get at a reasonable price, but research indicates that brass and bronze are "similar" metals and not good for bearings... Well, I could use steel then; it would be better... And then my eye fell on the 1m length of 17mm round PTFE I bought more than a year ago at a whim (and very good price).

Well... Why not?... I don't see plastics used a lot on model engines, but it's supposed to be as slippery as snot, so should make good bushes for this application. This engine will never be run on steam, so the issues with heat and water porosity shouldn't be a problem... There are two problems though; a) Would it be acceptable to use a synthetic material in a model like this ? and b) I've never tried to machine PTFE - not to any sort of accuracy anyway.

As to a) - It "feels" wrong, but then again, I wonder what the Verburgs, Duclosses and Spareys would have done; Some of their build specifications seem to use cutting edge materials in terms of what was available when they built their models, so I'm not going to feel too bad to add a bit of new technology...

And as to b) - Well, there's always a first time 

Decision made, I started; I just used my regular HSS tools that I use on everything; I just made sure all the cutting edges were honed sharp. Cuts easily, though I had some chatter as I didn't add tailstock support right from the start, but even parting off is a breeze ;D - small diameter bush done:





Bigger diameter bush in-making:





Both bushes were turned on the OD to a press fit in the columns. I'm surprised; it was easy to accurately turn the plastic and get fairly acceptable finishes; I expected to struggle a bit with that, but it turned out rather well. Pressing the inserts into the columns made a fairly significant change on the ID's of their bores. 
So I decided to try out my hand reamers on them; the 6mm one for the small shaft went well, and easily cut the bush ID to size again without any complaints.

The 12mm reamer was another matter; it wanted to chatter - severely... I was trying dry cuts, so I decided to try a little lubrication... But what scratch.gif. I settled on a squirt of the synthetic oil/water mixture I use when parting off steel; it worked a treat and the reamer smoothed right out and cut nice even chips out of the hole woohoo1

For today's work, I ended with this lot:





I'm surprised by how well the PTFE bushes work ;D:
[ame]http://youtu.be/D8wbTMHXql8[/ame]

The bush on the thin axle looks like [email protected] though, so I think I'll make an aluminium insert to press in with a smaller bush that will be hidden by the flywheel hub later on. I can make the ali insert nearly invisible and things should look nicer.

Kind regards, Arnold


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## mklotz (Nov 5, 2011)

Arnold,

You may find it easier to separate the tap extension function from the tap torquing function...






At only 0.25" diameter, this one will get into fairly tight corners. It has my usual floating alignment pin to keep the tap square to the work. The small tap wrench can be fitted onto it anywhere on the flat; its screw bears on the flat.


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## steamer (Nov 5, 2011)

To clean up the face of the boss was another matter; one cannot get close enough without damaging the center; something I REALLY do not want to do. So I moved away the tailstock, and with a narrow strip of emery pressed against the face with the forefinger of my right hand, I started the lathe; the pressure keeps the cylinder head engaged against the collet chuck, and because the contact area against the paper is larger than that of the emery on the face, there's sufficient drive to finish it. NOT the best way to do things; it would be better to stick the cylinder head to a mandrel (with superglue or double sided tape) or clock it up in the 4-jaw against a backstop to finish machining.



Actually that is an excellent way to face it....even writing paper should have enough grip to do what your doing....

Dave


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## arnoldb (Nov 6, 2011)

Thanks Marv  - that's a neat idea; another project for a rainy day then... I'll have to make ones for my smaller taps as well.

Dave, thank you; I won't disagree with you then ;D.

Today's four hour stint was done on the cam ring; it's not finished, but at least some progress.

I printed out the list of machining diameters (Many Thanks goes to Gail Graham for making up the spreadsheet I used), jotted down some notes of things to keep in mind on it, and sawed a bit of 2mm brass plate from some stock I have:





The plate was smeared with some permanent marker ink, and laid out for the most important bits:





On to setting up for machining, and oh dear; it's too big for my rotary table:





But it will fit on the lathe's face plate if I mount that to the RT ;D:





I found a bit of wood off-cut from last year's kitchen renovations, and mounted the workpiece to it with some self-tapping screws through the center bit where the screws will be inside the cutting tool path. After that, I drilled holes through the corners where excess will be, but spaced to match up the face plate's slots when the workpiece is centered:





Mounted the face plate on the RT, and centered the RT on the mill as well as zeroing the X and Y handwheels - making an additional note on the cutting chart as to which direction I was moving the table when zeroing the handwheels:





Then I mounted the workpiece on the face plate, lightly tapping it till I could get it as centered as possible. The mill's X and Y wheels were left strictly alone on zero. The idea is to center the workpiece to the center of the RT here:




I also tried to get the base reference as parallel to the X travel of the mill as possible by eye.

Once I was happy that the workpiece was centered, I cranked on X to check on the rotational orientation:




I'd eyeballed the rotation to less than half a degree, so I cranked the RT to bring the line on center and zeroed its dial.

One disadvantage of having screw-on chucks/faceplates is in a scenario like this. In this case, the face plate screwed on with it's slots offset by about 30 degrees, so I couldn't use the RT's own degree scale:





Oh well, a permanent pen can make a new scale; I'm going to work without any cutting fluid, so the markings won't be washed off:





Next I bodged up a DRO - One day I'll get proper DRO's but for the most part I don't mind reading the handwheels:




 :big: - I did say "bodged up" :big:

A final check of everything later, then a cup of coffee, pulled up a chair, and started... I'd calculated the cutting path for a 12mm cutter, so I drilled a 10mm hole to start things at the first coordinate after locking both X and Y axes on the mill and the RT's table. The hole is to give the cutter less material to cut away for a start - and prevent things moving:





Then I started with the 12mm cutter - same location and drill it out to size, mark the first coordinates on the sheet done. Then the roundabout began... Unlock RT, feed 2 degrees, lock, unlock X, dial in the new coordinate, lock, drill new location, mark as done on the sheet. Repeat. About 60 degrees later:





I stopped for the day at 178 degrees:





It takes about 45 minutes to do 90 degrees and a LOT of concentration (maybe I'm just a slow worker :big. One mistake, and I'll get to start all over :-\ And it is a bit of a mind-numbing process, so better to carry on when I'm fresh. That's why I put a new battery in the caliper; so it can "remember" the last reading, and why I meticulously marked off each position as it was done and the state of the mill when I started; at least I can stop and pick up from there later.

Regards, Arnold


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## arnoldb (Nov 13, 2011)

After a hectic work week and most of my weekend spent on getting an additional data center going for my company I finally got some shop this afternoon.

Finished off the last 180 degrees of the cam:





Drilled the two 3mm mounting holes:





I nearly forgot to clamp down the outer bit to the wood block before removing the bolts holding everything to the face plate... Fortunately I realised just in time and added a couple of screws through the mounting holes to keep it in place. The whole lot needed to be moved on the face plate to the outer ring center to finish things off, and if it moved it would have lost its place on the center piece that has the center position marked! :





Of course, last weekend in a blinding flash of idiocy I didn't drill additional mounting holes offset with the required 8mm from the initial ones, so no mounting holes could align with the face plate slots once I moved the workpiece to the new center :big: - So I grew a forest of clamps to finish the rest of the machining operations:





That meant I had to stop during machining to move clamps around to get out of the way - here is one of the stoppages to move a clamp:





Finally - all machining done on the cam three hours into the shop session:




Not a miss-step or anything, and that's the hardest part of this build done ;D - just some clean-up left to do.

A close-up of the cusps left by the machining process on the inside of the cam:





They look worse than they are; a little very light and careful filing with a 250mm fine half-round file brought the roughness down very quickly till all the cusps were barely visible and even in size right around the ring. Then I wrapped some 320 emery around a bit of 50mm pipe, and in careful circular motions around the ring removed the last visible signs of the cusps. All this was done very carefully; things needed to just be smoothed out; the shape mustn't change.

After a bit of file work around the outside of the ring to get rid of tool marks, and a rub over some emery and a quick rub with scotch-brite to give a brushed finish, the cam is done:





What do you know? - things fit together and is starting to look like an engine:





That's the engine half-way done then; so only 90% to go ;D

Regards, Arnold


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## steamer (Nov 13, 2011)

Nicely done Arnold....and that wasn't bodged up...that was Manufacturing Engineering at it's finest! ;D

 :bow:

Dave


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## Foozer (Nov 13, 2011)

arnoldb  said:
			
		

> That's the engine half-way done then; so only 90% to go ;D
> 
> Regards, Arnold



An optimist! You make it look so easy,

Robert


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## bearcar1 (Nov 13, 2011)

Yes, doesn't he tho'.......... :bow:

BC1
Jim


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## danstir (Nov 14, 2011)

Very nice work and a great prototype DRO.


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## arnoldb (Nov 15, 2011)

Dave / Robert / Jim / Danstir - Thanks Gents 

Stole an hour in the shop after work today; decided I'll fix up one of the eye-sores...

I removed the big ugly PTFE bushing from the "thin-shaft-side" bearing column, and turned up an aluminium filler piece and smaller PTFE bush, all for press fits:





The PTFE bush I did twice; on the first attempt I turned it's OD 0.02mm under the size needed, and that resulted in too light a fit...

The aluminium insert pressed into the big hole:





After a bit of filing and emery, the joint is nearly invisible:



You can click the photo above to see a bigger version; there it's more visible.

New bush pressed in - intentionally standing 0.5mm proud on either side of the bearing column:





That looks a lot better; in fact, once the flywheel is mounted, the plastic bush will be nearly hidden:





Regards, Arnold


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## Foozer (Nov 15, 2011)

Well your terrible, just terrible. Now I'm hooked, starting a sketch up of something to build. I don't think I can wing the Comber with what I have to work with and still keep my brain cell intact, but something close.

Gone some thirty days now with no smoking so its about time I started on something that will give me items to throw 

Like Plato? try Kafka

Robert


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## arnoldb (Nov 19, 2011)

:big: :big: Thanks Robert - I'll take that as a huge compliment ;D - I never knew "terrible" and "passionate" were synonyms :big:. You're thirty days plus ahead of me then... I need to quit as well, but I'm scared of what will happen to my boss and assistant........... 

Today's bit; I had a good shop session, so lots of photos...

I started work on the piston. Earlier in the build, I left the bore of the cylinder just a tad under the 16mm I wanted. That was on purpose; I have some 16mm round brass bar to make the piston from, but it needs a bit of skimming, so will end up under 16mm. I chucked the brass bar up in the collet chuck on the lathe, and faced it and then parted it down part-way on 5mm length:




Starting with a partial parting cut might seem silly, but there's a reason for it. If you look closely at the above photo, you'll see the burrs raised on both sides of the parting cut. If I left this for last, that would leave a ridge on the piston that I'd have to remove in some or other fashion - and there's no easy or accurate way.

A little later, and I'd used a small file to put chamfers on both sides of the piston, a free-hand oil groove with a triangular needle file, then turned it to final size and drilled it 2mm through the center:





After finishing the parting cut, I ended up with this:




The face shown is on the parted-off side; I still need to practice parting a lot more to get better finishes. The pronounced countersink on the hole was added manually; on both sides of the piston; these are needed for later steps.

Next I started on the forks. Drilled a 1.6mm hole through some 6mm thick square brass:





Then I mounted the slitting saw on the mill and used my height gauge to pick up the top of the block and set the slitting saw to height:





I just used my 0.5mm slitting saw to slit through for the fork bodies deep enough to later cut them off. Then added my 1mm slitting saw to the arbour to start cutting the forks - using the height gauge again - this left a 1.5mm wide slot; which I just slit to depth on the line I'd marked:





I then moved the mill quill down by 1mm, and slit again - leaving a 2.5mm wide slot, and then moved down and repeated:




If you look carefully, you'll see there's two stilling saws ganged together; a 1mm and a 0.5mm one. I really need to buy more slitting saws :big:

The block was then flipped in the vise and clamped down with a generous bit of cardboard to prevent things moving, and then the two forks slit off from the parent stock:





I then drilled the backs of the workpieces 1.6mm to tap M2 later:





After tapping and then some free-hand filing to round over the ends, the forks were done:





I needed some bolts to hold the cam to the base. Any old 3mm screw would have done, but I rather made my own. Here's some 5mm hex brass turned down and threaded with the tailstock die holder:





After some more machining, I had these:





The cylinder block needed some holes plugged - just two bits of 2mm brazing rod plugged in with high-strength retaining compound:




Ugly, innit ? ;D

Some more 2mm brazing rod followed to make the connecting rod; threaded both ends M2 to fit the forks and lock nuts. The piston have to be soldered on in the middle:





I used some aluminium drinks-can plate to clamp down the connecting rod with the piston in place. The plate keeps the piston on the correct height and prevents the vise from marring the connecting rod. Any solder that leaks through won't stick to the aluminium plate either:





Some soft-solder flux was brushed on before assembly, then I soldered the lot together with some electronics solder. I just used a small plumber's blow-torch to heat things up. It looks horrible here, but worked quite well:




Remember the chamfers I mentioned on the piston earlier on? - This is where they came into play; I made the hole in the piston a relatively tight fit to the connecting rod, but they had to be soldered together, and with the hole being tight the solder would not flow through. The chamfers provide the necessary area for the solder to make a reasonable secure joint.

Next I cleaned up some 6mm silver steel rod and drilled it through and reamed to 4mm, and parted off two rings 2.4mm thick:





Some brass followed, a tad under 4mm OD for a smooth running fit in the silver steel above, and parted off at 2.5mm lengths:





Makes for some OK bearings:





A quick trial-fit in the cam, and I could see how much to adjust the forks in the connecting rod:





All assembled together:




Please excuse all the oily marks and so on; when I assemble something for the first time, I use a LOT of oil. As can be seen from the photo, I''d also filed down and smoothed over the plugs on the air passages to blend in to the main shaft

There was a couple of tight spots on the cam with things all assembled; that was easily taken care of with some light filing and emery paper.
Things turned over fairly smoothly after that by hand, but wouldn't give me the easy flick with multiple rotations... and I was NOT happy; I'd built this engine so far to be EASY to run!
It was supposed to spin like a top...

At this point Thor threw a hammer at me noggin, and connected... HARD... ; Well, DUHHH - I've not yet drilled the main bearing column for an air supply or exhaust... - There is nowhere for the cylinder to suck or vent... So obviously it would not run well :big:- It needs a bit of breathing :big:


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## ShedBoy (Nov 20, 2011)

Just checkng the seal is what I would be telling the crowd 
Nice job Arnold, I would like to have a go at biulding one of these one day but that cam ring puts me of. You are an inspiration Arnold thanks for sharing.
Brock


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## arnoldb (Nov 20, 2011)

Thanks Brock  - the cam ring isn't really difficult - just a bit time consuming. It's a worthwhile engine to build; videos doesn't really do it justice - it has to be seen first-hand 

I didn't get a lot done today, but had quite a bit of fun ;D

First I drilled the column for the port holes - just 2.5mm straight through the center through both sides. One side will be tapped M3 for the airline connection, and I used a 6mm end mill to make a flat for the connector to screw up to:





Then I turned up the airline connector from some 6mm hex brass:





And then the real fun started; everything except the flywheel was there to give the engine a test run - so I tried it ;D:
[ame]http://www.youtube.com/watch?v=jHJ0YAyGoA4[/ame]

 woohoo1 - I didn't even know if it would run after all the changes I made.

I borrowed the flywheel off my grasshopper engine, and added that; after about 10 minutes of running, it could do slow too:
[ame]http://www.youtube.com/watch?v=gSra3sXZQoE[/ame]

It's not quite running on breath power; an almighty blow gets me a couple of turns, but I think I can get it running as I want with a slightly bigger diameter flywheel with most of the weight in the rim and some additional run-in time. 

So, it's flywheel, wooden base and final cleanup to go now...

Regards, Arnold


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## Foozer (Nov 21, 2011)

You never cease to amaze. 

I haven't even finished sketching up the gizmo to be my next project. 

Really is a nice looking engine you built.

Robert


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## steamer (Nov 21, 2011)

Excellent runner there Arnold!  And yes....you were checking seals...yes. ;D

Thanks for showing that!

 :bow:

Dave


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## lazylathe (Nov 21, 2011)

Another awesome build Arnold!!!! ;D
I am sure your sister is going to love it!!!! :big:

Hopefully one day we can all make it look so easy.... :bow:

Andrew


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## danstir (Nov 21, 2011)

Very nice!! Thanks for sharing your build.


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## cfellows (Nov 21, 2011)

Looking great, Arnold. You've got me wondering if a two cylinder version of one of these would be feasible...

Chuck


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## arnoldb (Nov 21, 2011)

Thanks Robert  - I'll give you a bit of a break then; I'm waiting to get some stock to make the flywheel from 

Dave, thank you Thm: - yes... Checking those seals... I might start believing it Rof}

Andrew, thanks  I hope she will like it ;D. It just takes a bit of effort to make it look easy; anybody can do it ;D

Thanks Danstir  - there's some more to come.

Chuck, thank you  I think a two cylinder is doable and should be a very nice runner.
The biggest problem would be the valve porting... the easiest way would be to have ports in both bearing columns feeding the pistons in parallel, with the the second cam offset at 90 degrees. The cams can be machined in one go with two plates clamped together, so that will not take much more time to do. A very interesting thought!

Regards, Arnold


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## arnoldb (Nov 27, 2011)

I didn't post yesterday's work, as a social commitment yesterday evening interfered :big:

Work started on the flywheel.

I got a phosphor bronze off-cut from one of my suppliers - not cheap, but it was the best I could do:





Started cleaning it up; this piece is just long enough to make two flywheels from. I've machined quite a bit of PB so far - always without any problems, but this piece was giving me some grief; it had soft and hard spots in it and was a bear to turn:





Parting it off was no fun; my rear parting tool wouldn't touch it, even though I'd honed it up super sharp! So I tried my old jig-saw parting bit and that ran through it without any problems:





After some more turning, I had the flywheel rim:





Next I turned up the flywheel hub, and drilled six 2mm holes in it for spokes, and a 2.5mm hole between two spoke locations to tap M3 for a grub screw:




While I had the dividing head mounted on the mill, I also drilled the rim for the spokes. The hard and soft spots made the drill wander quite a bit in each hole...

Spokes were cut from 2mm brazing rod, and one end of each cleaned up with a file:





The wandering of the drill in the rim made for a tight fit for the spokes through the rim; I had to resort to a small hammer to tap them in to just outside of the hub's radius. Then I set the hub on a piece of 6mm rod in the tailstock to help with positioning:





I put a drop of retainer in each hole in the hub, and also on the bits of the spokes still sitting outside the hub. Then I tapped each spoke in. I then moved away the tailstock, and with the rod left in the hub, I clocked the hub as center as I could by lightly tapping the bits of spoke still sticking out of the rim. Because the holes through the rim had wandered, axial run-out would have caused a very wobbly flywheel - so I checked further away as well, and used the rod to bend the spokes slightly to get the wobble out:





The flywheel was then set aside to let the retainer cure overnight. The spokes need to be filed or turned down later:





On to some woodwork...
Earlier this year while visiting, my father brought me a circular saw and a mounting table that my grandfather had very generously donated to me:




I haven't used it yet as I steer away from woodwork in general, but now was the time to try it ;D

The piece of teak I have for bases is quite difficult to cut with a jigsaw as I had done in the past - the circular saw did in seconds what used to take me many minutes to get done:





A final cleanup of the uncut edges of the block was done on the mill:





The piece of timber is very rough, and had spent quite a bit of time out-of-doors before I bought it, so all the faces are impregnated with dust and sand, so instead of breaking out the wood plane to plane down the flat faces, I used a very sharp HSS flycutter on the mill:




That left a really smooth finish 

Mounting holes for the engine base was drilled - part-way 8mm and then 4mm through - to match some M4 countersink screws I have:





I used a router bit to add a bit of detail - first on both cross-grain faces:




As can be seen in the photo above, the cross grain faces splintered out a bit, but the splintered bits are in areas that would be removed when routing along the grain - without additional splinters coming off.

After a final bit of work with sand paper, the base was looking OK:




I then lavishly applied furniture wax to it, and set it in the sun to have the wax draw into the wood a bit.

Work stopped there for yesterday - I'll carry on in another post for today's bit; have to finish uploading some things.

Regards, Arnold


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## arnoldb (Nov 27, 2011)

On to today's bit...

The good news is the engine runs, but bad news is there's some of the last machining photos missing, as my camera's batteries gave out after the first photo and the spare set was flat as well :

To clean the bits of spoke sticking out of the flywheel, I trimmed them as close as I could with a side-cutter, and turned up a mandrel to mount the flywheel on. I just filed a flat on it for the grub screw to locate on to hold the flywheel in position:





The batteries gave out and was put on charge, so some typing to explain what happened next:

I turned the outside of the flywheel down very carefully - till the spoke ends were off and I then gave it a very light finishing pass across the rim. Even though I worked as carefully as I could, the interrupted cuts and finishing pass brought the rim into a wobble. As I can't fiddle with it too much, I trued it up as well as I could, but it still runs slightly wobbly :-[; I should have silver soldered the spokes in instead of using the retainer.

The waxed wooden base was given a vigorous rubbing with a soft cloth, more wax applied and more buffing with the cloth. I could have painted the base with clear varnish, but I just like the way waxed & polished wood looks, feels and smells - even if it needs a bit of wax every now and then. My sis knows the drill with the floor & furniture wax 

I disassembled the engine and gave everything a final clean-over. All the finishes will be left as-is; the engine is fairly big (compared to my other builds) and I think polishing bits of it will be a bit too much on the eye. Also, polished surfaces need attention over time to keep them shiny, and the engine is actually quite delicate - if the cam ring bends slightly or pressure is exerted on the connecting rod or forks, it can go from a good runner to a non-runner in no time.

After cleaning and final assembly (and charged batteries), the engine looks like this:















I tried a couple of different locations for taking the finished photos; the above ones were the best lot from the lot, but this one is OK as well:





After some oil on the cam; a bit too much : - it still runs very well:
[ame]http://www.youtube.com/watch?v=rqDfsFwSgKI[/ame]

One of the aims of this engine was to have it run on breath power. It does, but still needs a bit more of running in. Please excuse the ugly mug intruding in the scene :big::
[ame]http://www.youtube.com/watch?v=flnqLdfuTIY[/ame]

My sister will hopefully visit in the next couple of weeks, then I can present it to her ;D 

Another fun build done... Time to clean the machines, make a bit of tooling, and then on to the next engine.

Regards, Arnold


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## Foozer (Nov 27, 2011)

Guess my break is over,

That thing is so cute, running slow sounds like a razor rubbing leather.


Robert


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## Jeremy_BP (Nov 27, 2011)

Very nice! :bow:

I'm astounded that such an engine can run on breath power. A gorgeous build, thanks so much for sharing it with us!


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## Blogwitch (Nov 27, 2011)

Another wonderful project Arnold, very nicely done indeed.

How long did you manage to stand upright after trying all that lung power?


John


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## arnoldb (Nov 28, 2011)

Thanks Robert  - You have made some drawings in the meantime Thm:

Jeremy, thanks, and it's a pleasure . Running it on breath power was a bit iffy; I'm surprised as well ;D

Thank you John .  :big: I Didn't feel faint at all, so not too bad then.

Kind regards, Arnold


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## kustomkb (Nov 28, 2011)

Very nice work on your engine Arnold. It looks great!

Nice work getting it to run on breath power. A testament to your workmanship.

Great photos too.


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## lazylathe (Nov 28, 2011)

Great looking engine Arnold!!! ;D

And a great build log too!!!

I am sure your sister is going to be very happy to be given that engine!!!

Andrew


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## bearcar1 (Nov 28, 2011)

BRAVO!!! Beautiful piece(s) of work Arnold, simply amazing. Breath power huh? Not too shabby at all.

BC1
Jim


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## Lesmo (Nov 29, 2011)

That's a little corker Arnold, your sister will be so proud to own it.

Oh and by the way, can you please send some of the background shown in your last location picture 
to us in the UK, boy do we need it.

Cheers Les


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## Ken I (Nov 29, 2011)

Arnold - another superlatively documented build and a great runner - thanks for the trip.

Re Chuck's suggestion of two cylinders ? I presume two side by side ar 90° to each other with two cam rings etc. etc.

Any comments ?

Dammit - my to do pile keeps growing an awful lot faster than my done list.

I stocked up on Windhoek to tide me over the festive season before you guys drink it all like you did last year.

Regards,
      Ken


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## arnoldb (Nov 29, 2011)

Kevin, thank you  - I don't know about workmanship; more like tons of blind luck and a bit of hard work :big:

Baie dankie Andrew ;D ; mailed sis a photo of it; she's driving down from the Caprivi in two weeks for some business here in Windhoek... 2800km round trip to fetch an engine :big:

Thanks Jim  Any progress on the boiler ? 

Les, thanks  - Unfortunately I can't send the background; I can take a nice big photo though that you can stick on the windows to block out the miserable weather ;D - Sounds like the winter's going to be a bad 'un in the UK again this year. Today's a bit wet with a thunder storm here, but us Namibians really appreciate a bit of rain 

Thanks Ken.  :big: Good idea to stock up; the Windhoek is now getting exported to the UK and about six new African destinations as well. I drive past the Namibian Breweries nearly every day, and it's amazing how much they've grown in the last couple of years. About two months ago, they did a major upgrade to the plant to increase brewing capacity to keep up with demand.

As to comments...

I did a very quick C-o-C of two possibilities (you can click on it for a larger picture):



Right, now we'll wait a bit for everyone to get over the laughing fit - I did say its *C*-o-C after all ;D
......

What I meant in my earlier reply to Chuck was the side-by-side ( *inline* is a better term) as shown on the left. One cam have to be rotated 90 degrees from the other, which means the air ports in the second bearing column also have to be offset by 90 degrees. 

I think what you're thinking of is what I sketched on the right, with the cylinders offset by 90 degrees and the cams in the same orientation.

I don't think one can get away with using just one cam ring - the cam followers would have to have additional "L" sections which will cause binding, as they will rotate on the cylinder axis and basically pinch up on the cam, unless one add crosshead guides - which should look really cool .

Like I mentioned in the earlier post, the valving will require the most thought, and I'm having trouble visualizing it... 
 :idea: I just had a thought though :big: - I actually HAVE two Coombers available to me for a few days; I think I'll try and couple their drive shafts at 90 degrees and see what the porting would have to be like... Give me a day or so and I'll post feedback Thm:

A twin cylinder would not require a flywheel, except for really slow running. The single has two power strokes per revolution and a twin offset by 90 degrees would be self-starting to boot.

While I spent a lot of time on the cam ring, I think it may just be possible to make a double cylinder a runner with a plain circle as cam. The cam on this one I built is only about 2mm out of a true circle, and the cam will get more pronounced with a longer stroke. I won't put the family jewels on a block for a plain circle cam though 

Regards, Arnold


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## Ken I (Nov 29, 2011)

It never crossed my mind to offset the cams 90° - I like your thinking.

Ken


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## arnoldb (Dec 10, 2011)

A bit of a follow-up for Ken 

I did some tests with the two Coombers this afternoon. They're not exactly a matched pair, as the one is a bit smaller than the other, but the information should be good.

For starters, I connected both engines along the crank shaft with a bit of rubber pipe - with the cylinders offset at 90 degrees to each other and the cams in the same orientation - and checked which way they wanted to run. Had to swap the porting around on the small engine; it turns out if connected like this, they want the intake port on the same side, which makes sense in retrospect:





[ame]http://www.youtube.com/watch?v=DlUrpPfsj90[/ame]

To test for the cam offset by 90 degrees and with the cylinders in-line, I set up like this:




[ame]http://www.youtube.com/watch?v=W8yHks3FCPs[/ame]

Now it seems so simple; if one wants to use the offset cam method, the intake port must just follow in the same direction as the cam is rotated...

Self-starting proved a bit problematic; but that could be due to the small engine not having enough oomph to turn the bigger one. The flexible "shaft" also caused some additional friction on the engines as it put extra load on the bearings, and also introduced a bit of axial flex.

I feel like a regular dunce now having seen what I was not able to think through, but anyway, there it is - hope it's useful for someone 

At least I had the fun of seeing two Coombers running in unison :big:

Regards, Arnold


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## Ken I (Dec 11, 2011)

Thanks Arnold, that helps crystalise it in my mind.

I'm also having trouble bending my mind around it - one moment I'm convinced it won't self start then a bit more thinking convinces me it will - I'm currently in the "it will" mode.

Like I said - one more thing added to the "to do" list.

Ken


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## peepfrance (Jan 30, 2012)

I would love to build this engine but does any one know how to construct the spread sheet for the cam profile.
Pete


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## peepfrance (Jan 30, 2012)

Sorry all, just read the group build thread and found Gails spreadsheet, many thanks for uploading.
Congratulations to arnoldb for an excellent build
Pete


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## arnoldb (Jan 30, 2012)

Thanks Pete - it's a fun engine to build, and draws a lot of attention when people see it 

Kind regards, Arnold


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