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| Building another Stirling |
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| cidrontmg:
Hi Stilldrillin, NickG, I havenīt used PTFE for a piston before, so it well might not be a good idea, but still worth trying. I can revert back to the graphite (I still have it...) if itīs a no go! I just didnīt feel like turning graphite right then. I had other engagements that evening, and didnīt want to show up there looking like someone just rescued from a coal mine... Iīve turned graphite a couple of times, and it makes an awful mess. At least it did with me! :lol: Experimenting is certainly in the books, thatīs the main reason for building this engine. I also want to experiment with other displacer sizes and materials. And balancing the engine, etc. Teflon and graphite, although both very low friction, are quite different as to thermal expansion. Graphite-not at all, PTFE-plenty. In this particular Stirling type, the work cylinder always stays cool, so I hope PTFE will behave. If not, too bad, and on to something else. :) What Iīm worried about now is balancing the engine. That connecting rod is sturdy, but boy is it heavy! Drilling holes in it (or grooves) will make some difference, but Iīm afraid not nearly enough. Taking off some material from the crank disk will also make a bit of difference, but still not enough I think. Lead weights opposite the crank pin... Might be... Thanks for watching, more on the way. :wave: |
| cidrontmg:
Not much. Did another flywheel to experiment with. Rather, it was an old brass flywheel that had an 8 mm hole. Too large, the crank axle is 6 mm. I guess I could have done a split taper fit, but it also had a smallish hub, nowhere near the +/- 22 mm needed (the engine will have a 20 mm stroke). So I made a plug, cut a 5 mm disk of 30 mm brass bar, and soldered them together. Then I cut two lobes away with a 2.25" face and side cutter (and didnīt take pictures :bang: )... And then Loctited the plug in the flywheel (green goo in the picture). Itīs now waiting to harden, will drill and ream it tomorrow. And probably drill (again...) 5 holes to make it lighter. :wave: |
| Stilldrillin:
Crisp work Olli! :clap: :thumbup: Mine never looks so good....... ::) David D |
| cidrontmg:
A few bits more. I cut some glass. I first cut the flared portion off the test tube, to get a feel how it works. Not too well, seemingly, because I broke the flared end... This doesnīt seem to be genuine Schott glassware, although itīs branded as Duran. Or maybe Schott has a factory in China... So a bit more care, and another trial cut. I just need 78 mm from the bulb, and thereīs 200 mm of it. Better this time, but not good. One more cut, this time with feeling, at the right length. Third time lucky, seems like the real McCoy. The cutting tool is next to the pieces, a "Dremel" diamond disc, definitely made in ROC. This is still the first test tube, I bought two. The tube needs a hole in the displacer cylinder, so it had to be bored to size. The piston rod is 6 mm, and now I have bought some more silver steel (drill rod), and there will be two Oilite bushings to guide and to seal it. The displacer will be some 25-26 mm dia, the glass tube is 27 mm inside, so the rest of the displacer must be bored also to 27 mm. There must also be a small step (+/- 10 mm long) for the test tube to enter, its outside is 29 mm. And enter it does. Test tube in place, with the O-ring, and a bit of silver steel with the bushings. Bushings pressed into the displ. cylinder. And another mockup. Seems to be rather square and reasonably well aligned. Itīs not missing much, the displacer proper and its connecting rod. Might run during the weekend. Or maybe not... :) :wave: |
| NickG:
yep, nearly there Olli :thumbup: , I'm confident it'll run - your machining looks spot on. Nick |
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