A 15cc sidevalve opposed twin

[Ken I]

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

Looking good so far.....

Regards, Ken

 

[Peter Twissell]

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.

 

[Ken I]

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

 

[Peter Twissell]

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.

 

[Peter Twissell]

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.

 

[Ken I]

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

 

[Peter Twissell]

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

 

[Willyb]

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

Cheers
Willy

 

[aka9950202]

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

 

[ajoeiam]

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.

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?)

 

[Peter Twissell]

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.

 

[propclock]

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

 

[ajoeiam]

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

 

[Peter Twissell]

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.

 

[Peter Twissell]

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.

 

[Peter Twissell]

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.

 

[Peter Twissell]

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.

 

[Ken I]

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

Regards, Ken

 

[Peter Twissell]

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....

 

[Basil]

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.