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| Building another Stirling |
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| madjackghengis:
Hi Nick, that engine is really moving along, and should be running here, shortly. Cutting glass is always a bit dicey, I've had good success with thin tubes by wrapping a cotton string around and tying it off, then putting some lighter fluid on it and lighting it, and hitting it with some water when it is about burned out, cracking it off pretty cleanly where the string was. Some care with a propane torch, taking lots of time to heat up the edge evenly very slowly, and the edge can be melted to a nice round profile, and eliminating cracks from starting from an unfinished edge. I always practice on the throw away piece because I never can be patient enough until I've cracked on before sucess strikes. I'm wanting very much to find a couple of test tubes myself, with all this inspiration. That ought to be a fine running engine when you're done with it. :bugeye: :poke: mad jack |
| cidrontmg:
Hi madjack, the way you suggested (with a "burning string") is also good. I cut the tubes for the previous engine that way. For the other engine, I bought 4 test tubes (showing great confidence in my glass cutting abilities..). I cut them all that way, all broke exactly where intended. Itīs also a very good idea to "polish" the cut edge with heating. Slowly is the key word, and careful... I overheated one of the tubes, and it instantly began to creep. See the left side on the pic below. Itīs not round anymore :bang: The tube is usable, thereīs tolerance enough in the cyl. bore. But if it ever comes into contact with the ali cylinder wall, itīs fairly certain to crack. Borosilicate glass develops hairline cracks very easily, it doesnīt shatter to small pieces. I went to cutting with a diamond disc, although the burning string method works very well. But I also wanted to try if I can cut an opening in the cylinder side. Havenīt tried that yet, but I will :D Test tubes usually canīt be bought one off, they come in lots of 10-50. Not that it matters much, theyīre cheap(?) in bigger lots, and you often need more than one :) One source for single/a few tubes is http://www.bengs-modellbau.com/material/buildingmaterials/index.php theyīre in Germany, the same site in German http://www.bengs-modellbau.de/ the German site is far bigger. Good quality, lots of hard-to-get things, and they send very fast. No connection except a happy customer :thumbup: |
| cidrontmg:
The end in sight. The only piece missing is the displacer, and that has caused some head scratching. Seems I donīt have (and canīt quickly arrange) 25-30 mm aluminium tubing. :bang: So what else is there... Plastic - no. Wood - no. Some heavier metal - ehh, no... A cigar case would be just about ideal - except I donīt have one that big. Might need a Robusto- or even Gordito- size. I have some cigar tubes, but the biggest is 16 mm dia. Not nearly enough. It is of course possible to make a tube from a solid piece of bar. Starting with a 30 mm, and making swarf and throwing away some 95% of it just doesnīt sound good. Hm. What comes nowadays in aluminium cases... Even many cigars come now in plastic tubes... After rummaging through some accumulated and increasingly unlikely trash (it tends to accumulate...), I hit the jackpot. An electrolytic capacitor, quite old and most likely dried up years ago. Outside dia. = 25.5 mm. Hehe. Just what the doctor ordered. So I opened it up, by turning a bit away in the lathe, and stripped it of its (dried up) innards. It turned out to have massive amounts of rock-hard asphalt inside. I cleaned it away with paint solvent, and got just about everything out, but it was a struggle. I then turned an end cap for it. British made even. And then glued the end cap in place with Loctite. And itīs a nice fit in the tube also. So tomorrow, Iīm going to finish it. I think Iīll wipe the texts away, and polish it slightly. Thereīs a few dents in it, but I hope it will do. At least until I get some bigger cigars in ali tubes. :) Thereīs also the need for a bigger spirit lamp. Iīll first try, and hope it will work with the smaller engine lamp, but of course this engine needs its own. Back to scrounging the scrap buckets... :wave: |
| madjackghengis:
Hi Oli, that capacitor turned out to be a nice fit, and leaving the printing on it leaves something interesting for people to wonder about, so that was a good job. Looks like you should be down to the end pretty quick here. I take it the test tubes hold up well to heat and you don't have to order special ones. I want very much to have an open and visible displacer, just to add another visual component to the engine, but the only tube I have is tiny, only about half an inch o.d. I definitely need to order some test tubes of substantial size. I like very much the way you have the power cylinder and the displacer cylinder side by side, I think it makes a very good looking engine. I'm looking forward to seeing it run. :bugeye: mad jack |
| cidrontmg:
First setbacks, one minor, another major. The displacer piston (the electrolyte cap.) is, I think, too short. I had to cut the glass cylinder (twice) to get it short enough. The piston should almost hit the cylinder bottom, and also almost hit the glass cylinder, at the resp. dead centers. Now it does, but the glass cylinder is a stump. Not looking good. Iīm fairly certain Iīll have to make another piston and cut the other test tube. It might work as it is, but thereīs a bigger problem. That (displacer) piston rod leaks furiously. When I flick the flywheel, it goes swoosh, swoosh, with the power piston going up or down. I made sure thatīs where it leaks, with soap suds. :bang: As you might remember, there are two Oilite bushings to guide and to seal the piston rod. They seem to guide it well, but the seal is non-existent. No wonder the piston rod was so very free to move... In the previous engine, I used the same construction, except the piston rod is 4 mm, here it is 6 mm. And in the previous engine it works perfectly. Blast. :doh: I didnīt think that would be a problem... Now, Iīll have to push the bushings out, and then make a tighter bronze bushing (not Oilite). The piston rod I think Iīll keep, it was quite hard (sic) to make. I have a 6 mm reamer, remains to be seen if that will finish the bushing airtight, but still freely moving. Another possibility would be a Teflon bushing. The Oilites are 10 mm dia and 10 mm long each, so there would be 20 mm to give guidance to the rod. Should be enough. Or maybe use one Oilite and replace the other with Teflon. This will need some experimenting. But it certainly wonīt even attempt to run with that kind of a leak. So it ainīt over till the fat lady sings. And she hasnīt started yet. :wave: |
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