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| Brass Stirling (#3) |
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| arnoldb:
Nice going Olli :thumbup: :lol: I don't blame you for not wanting to have anything to do with lightening - Had my own close call with it about 14 years ago... Was outside and just felt all my hair starting to raise... Hit the deck and it hit a tree about 15m away from me. I keep inside when there's thunder in the air now, and still prefer fiberglass fishing rods to graphite compound ones. :beer:, Arnold |
| sbwhart:
You're making a real nice job of that engine Ollie :thumbup: :thumbup: :thumbup: :thumbup: can't wait for the video of it running. Stew |
| NickG:
Olli, I've never thought that about CSk screws before but you're right, they do look classy. Good luck hope to see another runner very soon then :thumbup: |
| madjackghengis:
Hi Olli, looks like you're moving right along with the next stirling, and things looking up with that thin stainless. "And bored the power cylinder and made a piston. Itīs a blind hole, so it cannot be reamed. I let the boring bar (thickest I have) run several times slowly through the bore without advancing, until it didnīt shave even dust any more from the bore. The piston is a 7.2 mm ali bar which is pushed to a 7 mm hole in the Teflon bar. No need to glue it, I donīt think I could get it apart without breaking anything. When the air from the hole in the PTFE has been pushed away, thereīs an almost perfect vacuum holding the pieces together, if you try to pull them apart. And of course the ali "heart" will stiffen the Teflon for turning it into size. The cylinder bore is 13.7 mm, that seemed like "enough". The engine in the drawing has a 12 mm cylinder. This engine will have a shorter stroke, however." I took the quote, only to say, as long as you don't bottom out the power piston, the bore can be reamed, and in situations such as yours, I've reamed a cylinder and then carefully run a boring bar to the point where the reamer's taper starts, and bored out that bottom little bit, getting perhaps an extra half a thousandths clearance for that little bit, but not affecting the compression significantly at all. My lathe has a tendency of getting swarf under the rear flat way, and goes from turning straight to a slight taper without warning, if I don't specifically clean out that way and under the back of the cross slide, so I use reamers for cylinders when possible, but with the DRO, I can move a boring tool right down to the end of the reamed part, and make the cut through just the part of the taper of a machine reamer while avoiding touching any of the reamed area. By the way, I'd be inclined to use a piece of copper tube, say eighth inch or so, for the line between displacer and power cylinders, and solder it, just to be sure its airtight with minimum dead space. :thumbup: mad jack |
| picclock:
Hi Ollie Really nice work there - and if the finishes are as good as the camera makes them look, it will be quite a stunner. However, a slight word of caution (just call me Doctor Doom). PTFE is a fickle material when it gets warm :wack:. It has a high coefficient of expansion and gets very floppy. I used it in a temperature controlled oven once for testing TV Triplers for export to the Emerates. And despite using 3/8 inch thick material ran into significant issues. An easy check would be to put your piston/cylinder assembly on a radiator or in an oven to check for fit when its warmed up. I hope I'm wrong about this but .. . Look forward to seeing it running. Best Regards picclock |
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