The Green Twin Oscillating workshop engine

[Woodguy]

In August 2010 I saw an engine on the Preston Services site which I really liked (image 1) and wanted to build. Many of you may remember it. I copied the 4 images that Preston provided, and with the data in the advert (12 inch flywheel, approx 2 x 5 bore x stroke) I proceeded to create a (very bad) 3d model of the engine at 50%- a size which would fit my equipment well.

Fortunately friend Pat down in Memphis, who is a wizard with Solidworks, took pity on me and redrew the engine. A rendering of that model is shown as image 2 below.

I had originally wanted to do a barstock version of the engine, but Pat persuaded me that it really should be cast and volunteered to produce the castings.

At that time I was a member of a local makerspace which had a 3d printer, and I used it to produce the basis for patterns of the small parts (image 3) as well as the bosses for the base, suitably scaled and with draft added. I had difficulty getting a flywheel printed as the printer kept failing late in the prints (costing me money), so I located a firm in Knoxville near Pat which produced a beautiful set of flywheel patterns and delivered them directly to Pat.

By this time (we're in 2012 now), Pat had acquired a 3d printer and using it created the basis for a cylinder pattern. A good deal of hand work was necessary to get the 3d patterns to work properly.

Pat built a foundry and went through a number of furnace designs and numerous iterations of molding strategies (foundry work has a long learning curve), but eventually (late 2015) there were castings in our respective workshops.

A few months later and we have the engine you see in the photos (images 3,4).  It runs, and while there are fasteners to replace and some fine tuning to do, I'm calling it basically done and I'm going to just look at it for a while.

Pat's engine is not yet finished, but he has run it with one cylinder - and his is green.... (last image)

Don't you love it when a plan comes together....

Pat has documented his build and plans to publish details of the build with the drawings in a magazine article. There are no plans to make castings available.

I deleted the sound from the video because of the compressor noise.

<a href="https://www.youtube.com/watch?v=fto10Q5hq0g" target="_blank">http://www.youtube.com/watch?v=fto10Q5hq0g</a>

[b.lindsey]

Fine result on both engines Woodguy, and a great runner too. I like it and the gray finish on yours. Thanks for sharing it!

Bill

[Jasonb]

That has turned out very well, Pat did send me a video of his running on one cylinder recently and mentioned you were further ahead and certainly runs smoothly on two cylinders.

J

[Jo]

Yes I do like that engine  .

Shame it will be published over the pond

Jo

[Jasonb]

I'm sure in this day and age that you could buy digital copies of most magazines that are likely to have the article or there is always good old mail.

[Woodguy]

Thanks for the comments. Here's a postscript.

After the castings were completed, Pat was able to acquire the original engine from Prestons, The engine disappeared after it was originally offered by them, but then reappeared some time later. I always assumed that someone had bought it, perhaps for purposes of modeling it, but nothing turned up on the forums.

As it happens, Prestons didn't actually measure the engine, or they would have stated the engine's flywheel as 10 inch not 12. As a result, our engines turned out to be almost exactly 60% of actual size. It's uncanny how close it came. The model has a 6 inch flywheel, a bore of 1.25 inches and a 2 inch  stroke.

Here is the original engine running on air in Pat's shop. It's a nice runner. I have hopes that mine will run that well once broken in.

<a href="https://www.youtube.com/watch?v=E6ztwggvmm0" target="_blank">http://www.youtube.com/watch?v=E6ztwggvmm0</a>

[Jasonb]

I was shown that earlier today, sure does run slow.

Is it just me or would it better running in the other direction

[Woodguy]

I wondered about the direction of rotation myself. It does look a bit wrong rotating that way. My plan was to  mount it on a base with plumbing to a reversing valve, but who knows if I'll ever get  there. It's been an interesting journey in any case. Lots of firsts for me and I've certainly never looked at engine photos with such intense scrutiny before.

[dvbydt]

That's a very competent reproduction of that engine.

I too was inspired by the Preston Engine and modified the design so I could make a barstock version.
Video and pointer to HMEM build log :-

<a href="https://www.youtube.com/watch?v=AlaB3aKpenc" target="_blank">http://www.youtube.com/watch?v=AlaB3aKpenc</a>

Ian

[gary.a.ayres]

Woodguy -

Superb replicas of the almost mythical Green Twin.

And your friend owns the original too!