Stirlingengineforum.com

Is there any way to get a power piston to work in a glass tube if the ID of the glass is out of round by 0.003? I can't find glass tubing with precise ID's.

Maybe. here is what master stirling builder Jan Ridders says about glass tube:
"The tolerance of the inner diameter of the tube in what the working piston is running must be fairly small: +/- 0.03mm or smaller; most common test tubes don’t fulfill this requirement. You can find suppliers for this kind of good quality glass tubes on internet also (try “Schott Fiolax” or “Duran”),""

.03mm = .001" So plus or minus .03mm = total variation of .002"

Bengs Modelbrau sells suitable tube at at http://www.bengs-modellbau.com/material ... ttubes.php
They say their tube is plus or minus .05mm, which equals .002" almost. So total variation of .004", which seems like a hell of a lot when on a metal cylinder the fit is always made to be less than .001" clearance.

The other way round the problem might be to use a leather cup seal on a slightly loose piston, this will comform to any slight out of round. Ian S C