Stirling Engine displacer

[Technical Ted]

Ted,
Thanks for the post - I'm in the middle of building one - about half the parts done.

Nice to see one running - its a nice running bar ornament - the reason I chose it.

How did you cut the test tubes - I bought 5 - I hope to break not more than 4 .

Ken

Ken,

I put the test tube in a collet in my lathe and cut it off while rotating it slowly with a high speed grinder and small diamond Dremel cut off wheel. This worked very well once I got things figured out. At first, I was holding it too tightly with the collet and when the grinding wheel cut off the excess the tube in the collet cracked. Once that extra material and it's strength were removed, the remaining tube couldn't support much pressure.

I found that just very, very lightly holding it was the trick. Using spray mist also helped with any thermal cracking. Although there is a squirt bottle in the picture, I switched over to my Noga mister.

If you liked my first video, check out the link below where I build 3 and they are all running on my mantle.

Ted

 

[Ken I]

Ted, thanks for the response - that was what I was going to try but your tips will help I'm sure.

Did you flame glaze the edges after cutting or did you deburr with diamond files or leave them as cut.

Another method I was thinking of trying was to diamond score the tube, fill with cold water to the score line - wrap an Inconel heating wire around the tube - just above the score line / water level and apply heat - causes the tube to fracture at the score. I've seen this done but never tried it myself.

Will go with your method first.

Great video of three running.

Regards, Ken

 

[fcheslop]

I used to cut them in the lathe using just a diamond file but as I became more interested in building Stirling engine with glass displacers and hot caps took the time to build Jan Ridders simple cutting jig
The only mod I did was to use the flexy drive of my dremel clone to keep it well away from the water
It does not take a lot of effort to make the jig and well worth the time as I now rarely have a failure
cheers
glasscutter_frametekst

 

[Technical Ted]

Ted, thanks for the response - that was what I was going to try but your tips will help I'm sure.

Did you flame glaze the edges after cutting or did you deburr with diamond files or leave them as cut.

Another method I was thinking of trying was to diamond score the tube, fill with cold water to the score line - wrap an Inconel heating wire around the tube - just above the score line / water level and apply heat - causes the tube to fracture at the score. I've seen this done but never tried it myself.

Will go with your method first.

Great video of three running.

Regards, Ken

Hi Ken,

All I did was touch the end up with some fine emery paper on a flat surface. I just wanted to make sure that the edge wasn't sharp as to not cut the o-rings when inserted inside the body.

I only had one problem building these engines and that was with the cast iron bearing. Seems like a simple part to make, but any, and I mean any, misalignment in the hole in the center and you will have a problem. Friction here is a killer! See my post here where I helped another member with his:

https://www.homemodelenginemachinist.com/threads/stirling-60.30328/

The struggle was getting the tiny drill to stay straight so the hole was perfectly concentric with the OD. If it's cocked off; problem. And all my different attempts (except for the last method) I could measure that the hole had walked off center on the far end. These little drills are just too flexible. My final solution that worked very well was to mount my small Albrecht chuck in my tool post, chuck up on a gauge pin, and indicate it dead true with the spindle of my lathe. Then, using a new center drill I spotted it, then drilled with a new drill, then finally finished with a reamer. Seems like a lot of work, but it's even more work when you can't get the engine to run!

Remember as you build yours that these engines have very little power and any friction and/or misalignment will be a major impact on its' operation.

Good luck,
Ted

 

[Ken I]

Thanks Ted & fcheslop - I am well aware of concentricity issues - you simply can't drill a hole down the centre of barstock due to corckcrewed nature of the grain.
Bigger holes you can drill, bore & ream but small holes are always a problem.
I do a lot of bits with 2mm holes that need to be dead concentric - I rough machine the O.D. and ream the bore - locktite it to a sacrifical turned mandrel - finish the OD and heat off an clean up.
A PITB but it works every time.
See "I can't drill straight" on my elbow engine build
https://www.homemodelenginemachinist.com/threads/six-shooter-elbow-engine.15958/page-3
This with 4mm reamed holes for the pistons - mounted on a mandrel to get the OD concentric with the bore.
Regards, Ken