Stirling Test Tube

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robwilk

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I am looking at having a go at a Stirling engine the plans i am looking at call for a test tube 15.6mm OD 54.5mm long.
I realise that if i got a test tube 16mm OD a small change to the drawing would not be a problem but all the tubes i have seen on the Internet either have a rim around the neck or are to long.
So my question is can i get a tube that is to long and have a rim and cut it down obviously without breaking it to the desired size. And if so how do i go about it. Any advice would be grateful.
Thank you.

Rob......
 
A guy who built one of the lamina-flow engines used a diamond cut-off wheel (Dremel tool type). Hold saw stationary and rotate the tube to score/cut it. Says it worked fine.
 
........I cut all my test tubes for Stirling with a triangular diamond hand file held up to the tube as it rotates in the lathe. I wrap some masking tape on the closed end of the tube for the jaws to grip and spin 3-6 hundred RPM. Test tubes of different brands have slightly different wall thickness and those that do have a heavier wall leave a cleaner cut with less chance of breakage. I find that if you have a jagged edge as it just cuts through you can clean up its end holding against a bench grinder. Always order borosilicate (PYREX) glass tubes. Also when you cut to desired length you can use a half round diamond file to tapper the cut end by hand so your piston doesn't snag as you insert into the tube if you are building a lamima type heat engine. I buy a pouch of these China special files for $10 at Harbor Freight and get test tubes locally at a lab supply.
 
Thank you for replying guys Now i know it is possible and have a few methods to try I will get some tubes ordered and make a start .

PS. Kevin thanks for the link. I loved the Pulse Mobile it is the first time i have seen one . Also loved the dance in the video but i would stick to the machining. :big:


 

Thanks Rob,

I won't be quitting my day job. ::)
 
Hey, I've got one running on youtube.com. Check it out.
BTW, the test tube length isn't critical. I've cut down the length a lot. I'm currently running the lamina on a tube about 3 inchs long. I place the tube in the lathe, turn it really slowly and hold the dremel wheel lightly against it.
My double o-ring idea for mounting the tube you see in the video is not so good cuz the lip of the tt has a smaller dia than the id of the tube. That makes it hard to assemble. Good compression is of upmost importance so watch your piston fit; no leaks in the seals either.
[ame]http://www.youtube.com/watch?v=OsEipETufyI[/ame]
 
Jim thanks for sharing that . It is a beauty :bow:
Also very descriptive commentary.

Rob......
 
Jim: That is a very nice running Lamina. I have done a lot of experimenting with Lamina engines and I found that plain steel wool gave a very noticeable increase in speed compared to stainless steel wool. Plain steel has a much better heat conduction than SS.

The opposite situation arises when building a Stirling with a hot and cold end. Then SS is preferable for the hot end to avoid conducting heat to the cold end through the metal.
 
Nice engine and nice job on the video!
Thanks for sharing it with us!
 

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