Moriya Stirling Engine Build
Re: Moriya Stirling Engine Build
Russell:
When we were making those displacer pistons, we made the ends a light press fit in the tubing.
When pressing together, the thin-walled tubing would very slightly (measurable) expand. That press fit was sufficient.
RussN
When we were making those displacer pistons, we made the ends a light press fit in the tubing.
When pressing together, the thin-walled tubing would very slightly (measurable) expand. That press fit was sufficient.
RussN
Re: Moriya Stirling Engine Build
Thanks, Russ.
I don't actually understand why the displacer pistons need to be airtight. But everything I've read says that's important.
Edit: So then I read some more and find that maybe it's not important:
https://stirlingengineforum.com/viewtopic.php?t=663
You gotta love the internet, where you can find support for either side of any issue you care to debate.
-- Russell Mac
I don't actually understand why the displacer pistons need to be airtight. But everything I've read says that's important.
Edit: So then I read some more and find that maybe it's not important:
https://stirlingengineforum.com/viewtopic.php?t=663
You gotta love the internet, where you can find support for either side of any issue you care to debate.
-- Russell Mac
Re: Moriya Stirling Engine Build
I primarily did not want the piston to disassemble itself inside the displacer cylinder!
RussN
RussN
Re: Moriya Stirling Engine Build
Progress Report #9:Harold_V wrote: ↑Fri Mar 12, 2021 4:32 am You would have better success creating the cut using a mill and a rotab. You can plunge the cut instead of feed radially, eliminating the bulk of the material with a 1/8" end mill. Probably work best starting with a drill, though. Once you've achieved full depth, you'd rotate the table a few thou and take another plunge cut to full depth. It happens fast, as you'll use the quill of the machine to feed the end mill. You could then switch to a 5/32" four flute to widen the cut, then step over each direction for finish passes.
This general idea worked really well. I started by hogging out most of the material with a 5/32" drill. Then I nibbled away (using plunge cuts) most of the resulting scallops with an eighth inch end mill, and finally cleaned up the side walls with the same 1/8" end mill.
-- Russell Mac
Re: Moriya Stirling Engine Build
Well done.
RussN
RussN
Re: Moriya Stirling Engine Build
Thank you. It will be interesting (someday) to try the trepanning method again and see how it compares. I can see how the results might be about the same, and it might even be easier. For me, anyway, it's a royal pain to set up the rotary table.
-- Russell Mac
Re: Moriya Stirling Engine Build
Progress Report #10:
I made the rods for the displacer pistons and pressed them all together a couple of days ago. As far as I can tell, that all worked okay. I did put a bit of JB-Weld on the parts before pressing them together, just for insurance against leaks. With the rods held in a collet in the lathe, I measure maybe 3-4 thousandths of runout at the far end of the pistons. So maybe there is some hope that they won't rub on the inside of the cylinder.
Then I spent way too much time cutting out a bunch of gaskets. The white ones are the thick parts that thermally insulate the hot end of the displacer cylinder from the base. I wound up using Teflon for these. We'll see what happens with that.
-- Russell Mac
I made the rods for the displacer pistons and pressed them all together a couple of days ago. As far as I can tell, that all worked okay. I did put a bit of JB-Weld on the parts before pressing them together, just for insurance against leaks. With the rods held in a collet in the lathe, I measure maybe 3-4 thousandths of runout at the far end of the pistons. So maybe there is some hope that they won't rub on the inside of the cylinder.
Then I spent way too much time cutting out a bunch of gaskets. The white ones are the thick parts that thermally insulate the hot end of the displacer cylinder from the base. I wound up using Teflon for these. We'll see what happens with that.
-- Russell Mac
Re: Moriya Stirling Engine Build
rmac wrote: ↑Sun Mar 21, 2021 12:45 pm Progress Report #10:
Then I spent way too much time cutting out a bunch of gaskets. The white ones are the thick parts that thermally insulate the hot end of the displacer cylinder from the base. I wound up using Teflon for these. We'll see what happens with that.
-- Russell Mac
Instead of gaskets, try a thin layer of automotive silicone sealant, very effective if the mating surfaces are flat and smooth, with one side having a tiny circular groove.
The insulating spacers are a waste of time. A thin wall section of the hot cap leading up to the sealing flange, and the flange kept as narrow as possible for sealing purposes using silicone, make a separate clamping flange from 304 SS to hold down the hot cap. Bore this bolting flange for a close slip fit over the mating/sealing flange dia., along with a counterbore to receive a split ring that bears down on the sealing flange. Very effective with low heat transfer (less that an insulator), easily assembled and dismantled.
Wolfgang
Re: Moriya Stirling Engine Build
Wolfgang:
Since RMac has already made the hot cylinders, there is no reason to remake those for a different seal to the base.
The teflon gaskets should work fine, as long as they don't compress and "flow" with clamping pressure. That would be my only concern.
And that is a reason for the original non-compressible bakelite gaskets. Both strength and heat insulation.
Also, the other gaskets provide some thickness for correct fit of all the parts.
Russell Mac:
If you find the displacer piston is contacting the inside of wall of the hot cylinder, just turn/file down the bottom radius.
We had to do that on occasions. Your small runout should be just fine.
These Stirling engines work well as drawn. BTDT, many times.
RussN
Since RMac has already made the hot cylinders, there is no reason to remake those for a different seal to the base.
The teflon gaskets should work fine, as long as they don't compress and "flow" with clamping pressure. That would be my only concern.
And that is a reason for the original non-compressible bakelite gaskets. Both strength and heat insulation.
Also, the other gaskets provide some thickness for correct fit of all the parts.
Russell Mac:
If you find the displacer piston is contacting the inside of wall of the hot cylinder, just turn/file down the bottom radius.
We had to do that on occasions. Your small runout should be just fine.
These Stirling engines work well as drawn. BTDT, many times.
RussN
Re: Moriya Stirling Engine Build
Wolfgang:
Thanks for the hints. As RussN said, however, I would have to remake a bunch of parts to consider your suggestions. Maybe next time!
RussN:
I'm not worried at all about the displacer piston any more. The only remaining source of problems there is the gland, and I can make those over and over if necessary until I get them right.
-- Russell Mac
Thanks for the hints. As RussN said, however, I would have to remake a bunch of parts to consider your suggestions. Maybe next time!
RussN:
I'm not worried at all about the displacer piston any more. The only remaining source of problems there is the gland, and I can make those over and over if necessary until I get them right.
-- Russell Mac
Re: Moriya Stirling Engine Build
Hmm. I wasn't aware that this could be a problem. However, according to this info from DuPont (http://www.rjchase.com/ptfe_handbook.pdf), cold flow in a compressed Teflon gasket is negligible after a single retightening performed a day or so after the original clamping pressure is applied. So maybe another bullet dodged!
-- Russell Mac
Re: Moriya Stirling Engine Build
RMac:
"Cold flow."
I would suggest your operating temperatures are not "cold."
Just saying.
RussN
"Cold flow."
I would suggest your operating temperatures are not "cold."
Just saying.
RussN