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Green Twin Oscillator

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PatJ21/02/2016 03:18:01
45 forum posts
31 photos

When I first started working on the 3D model for the green twin, the plan was to build the engine using bar stock.

We eventually decided the engine just had to be cast, and so I started tinkering around with melting aluminum.

I had no clue about patterns or pattern making, and my Canadian buddy said "there is a guy on y-tube that shows how to make a flywheel pattern", and that guy turned out to be myfordboy (enginebuilder?).

So the first pattern for the green twin was a wood flywheel pattern based on myfordboy's methods.

My pattern making skills were extremely poor at the time, and so we went with a 3D printed pattern, but I have watched a large number of myfordboy's foundry videos, and credit him with much of the casting of this engine, since much of the pattern making and molding for this engine came from his shared knowledge, and inspiration from his beautiful engine builds.

There is a lot of talent in the world, and in GB in particular, and thank goodness these folks are kind enough to share their information.

Edited By Pat Jorgensen on 21/02/2016 03:18:30

Edited By Pat Jorgensen on 21/02/2016 03:19:56

Peter Krogh21/02/2016 04:00:20
213 forum posts
20 photos

The 'as cast' finish on that wheel, the spokes especially, is really fine and nice. I seldom see that good a finish on iron castings. So I must ask about the mould material. Is it petrobond?



PatJ21/02/2016 06:24:06
45 forum posts
31 photos

The first flywheel did use Petrobond, but I had a few sand inclusions where I think the iron overheated the sand and caused it to fail.

For the second flywheel and the remaining molds, I used a resin to bind the sand, and the sand was a very fine commercial grade round-grain foundry sand (OK-85 I think). The resin system is specifically designed to work well with cast iron temperatures, and I never had a sand failure after changing to resin-bound sand.

For non-iron castings, I have also used sodium silicate based binder for the same sand, and it also works well for metals with a lower casting temperature than iron.

Peter Krogh21/02/2016 11:19:19
213 forum posts
20 photos

Thank you, Pat. What resin system did you end up with?


PatJ23/07/2017 09:36:56
45 forum posts
31 photos

Sorry for the late response; sort of lost track of time here.

I used a polyurethane binder, but due to the fumes I have since switched to sodium silicate exclusively as a binder.

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