A 15cc sidevalve opposed twin

[Peter Twissell]

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.

 

[awake]

Clever fixturing is more than half the battle!

 

[Basil]

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.

 

[Majormallock]

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!

 

[Peter Twissell]

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?

 

[Majormallock]

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

 

[Peter Twissell]

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

 

[animal12]

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

 

[Majormallock]

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

 

[Peter Twissell]

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.

 

[Majormallock]

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

 

[animal12]

thanks
animal

 

[Peter Twissell]

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.

 

[Majormallock]

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

 

[Peter Twissell]

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.

 

[Majormallock]

Many thanks

 

[Peter Twissell]

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.

 

[Peter Twissell]

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.

 

[Peter Twissell]

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.

 

[Peter Twissell]

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.