# Thimble Engine



## Oldmechthings (Apr 26, 2008)

Perhaps You'd like an image of my smallest engine. It has a 1/16" bore and stroke. The flywheel is 1/4" diameter the crankshaft is .020". It is not all that much to see run, as it turns about 20,000 rpm and at that speed the eye does not catch much movement. It sounds like a mosquito in a power dive. The reason for the name is that it uses a thimble for a boiler.












  Even though it is one of my favorite engines, I did not build it. It was built by a young friend,Tom Morgan of Shelley Idaho. While attending a antique machinery show I picked up a used copy of the book Steam and Stirling Engines. I already had a copy, but the price was so cheap I could not pass it up. The next time that I seen Tom I gave it to him, because I knew he would put it to use. One of the projects in the book that caught his attention was the Thimble Power Plant by James Senft, because it looked like a real challenge. Tom made four of everything, hoping that he could get at least one operating engine out of them, but guess what? All four of them ran. So then I became a recipient of one of the engines. How nice of him.
         Birk ;D


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## Brass_Machine (Apr 26, 2008)

Birk,

Your friend did I nice job. I am always amazed by the really tiny engines. The use of the thimble is really cool!

Eric


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## kustomkb (Apr 26, 2008)

I have this book too, I am glad to see someone built it, I've always enjoyed looking at the pictures and maybe now am motivated to build it.
Thanks


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## BobWarfield (Apr 26, 2008)

That is so cool!

As I work on our Team Build engine, which is huge by comparison, I am becoming acutely aware of the need for magnification in many varieties in my shop. I have a head loup, but could use more. For this thing I could really understand the need for a stereo microscope.

It makes me think that a really cool way to display it would be to build a stand/base that incorporates a magnifier. Do the whole thing up in a classy brass format and it would be very sweet.

Cheers,

BW


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## Tin Falcon (Apr 26, 2008)

those littel engines are amazing I have not had the nerve to try one yet . I have the S & S book one and have seen the engines at shows. I built the large cousin mini-Kin a nice little runner. 




the fly wheel is 3/4 inch. 
That engine is a nice little gift. 
Tin


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## mklotz (Apr 26, 2008)

For those of you considering building the thimble engine, consider a few of these dimensions...

Steam ports require a #80 (0.0135") drill
Crankshaft built up from 0.0210" and 0.0312" steel rod
Main bearing is 0.062" diameter drilled through 0.021"
Cylinder retaining screw is 000-120. You need to drill and tap a hole this size 0.080" deep in a spigot that is 0.052" diameter. The flywheel retaining screw is also 000-120.
The spring is wound from 0.006" wire.

While it's doable, it's akin to watchmaking. Not a good first project.


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## Bogstandard (Apr 26, 2008)

When I built my tiny engine, it was twice the size of this one, and that caused a lot of problems, mainly, because it was free standing, unlike this one, was getting the air to it. I had to use a syringe needle as the input pipe.
Definitely not one for a beginner or anyone with bad eyes or a nervous disposition.

John


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