Tiny Stirling Engine

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mklotz:
Actually, it's a bit more complicated than that. One needs to take into account the thickness of the chuck jaws. There's a program on my page (ECCENT) that will do all the dirty work for you.

andyf:

--- Quote from: mklotz on December 29, 2010, 03:27:28 PM ---Actually, it's a bit more complicated than that. One needs to take into account the thickness of the chuck jaws. There's a program on my page (ECCENT) that will do all the dirty work for you.

--- End quote ---

Thanks, Marv. For me, life increasingly seems to be getting "a bit more complicated than that" :scratch: :(

I have had a go with ECCENT. Does the "pack to 1.5 times the offset" idea only break down when the dimensions of the work couples with the required offset are such that the work is not being supported by the flat faces of the "other two" jaws, but by their sloping sides, or are there other complicating factors?

Yours curiously,
Andy

mklotz:
Yes, as the work loses full contact with the two other jaws the geometry gets more complicated.
The program accounts for all this automatically.

For round stock, the ECCENTUB technique is much more stable since the work is fully supported on all three jaws.

None of these techniques are as good as the old four jaw, however.

NickG:
Thanks Andy and Marv - I completely neglected the fact that with the packing, the jaws have to open further - I just don't seem to be thinking straight at the moment. Now I've come to think of it I'm sure someone has shown me that page before Andy, it's amazing all this stuff I keep forgetting! Marv, I'll definitely be using eccent for the next one, thanks. I guess you'd have to be careful with smaller stock as there is quite a radius on the gripping face of my jaws.
Nick

madjackghengis:
Hi Nick, I just wanted to chime in, I have never crossed that page, and never really considered the whole issue geometrically, and thus my answer was wrong, as well. I've let the problem be an issue without ever solving it, and Andy was very helpful in clearing my head on this as well, if you don't mind my using your post to thank him. I think I will book mark that page, and have it when I need it. By the way, what program are you using to draw your designs with, if you don't mind my asking? I see them in the background and they look simple, but very nicely done. I wouldn't mind something more than scribblings on scratch paper, for drawings, sometimes intricate details don't get down on the scratch paper and get missed. By the by, with the LTD stirlings, the longer you make the displacer rod tube, the more effective it is in sealing, if you've got it reamed well, as John described, and if the rod is ground and polished. I don't know how far your Dad lives from you, but if you built the engine again, and fixed all the little issues it has, you could probably trade it out without letting him know, and let him have one that runs, after you work out all the bugs. I was hoping to do several presents this Christmas with small engines, but the flood sort of took up the past couple months, and I ended up with gift cards - nothing like the same. Keep posting and let's see a runner soon :poke: mad jack

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