Moriya Stirling Engine Build

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: GlennW, Harold_V

User avatar
NP317
Posts: 4557
Joined: Tue Jun 24, 2014 2:57 pm
Location: Northern Oregon, USA

Re: Moriya Stirling Engine Build

Post by NP317 »

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
User avatar
rmac
Posts: 787
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Moriya Stirling Engine Build

Post by rmac »

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
User avatar
NP317
Posts: 4557
Joined: Tue Jun 24, 2014 2:57 pm
Location: Northern Oregon, USA

Re: Moriya Stirling Engine Build

Post by NP317 »

I primarily did not want the piston to disassemble itself inside the displacer cylinder!
RussN
User avatar
rmac
Posts: 787
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Moriya Stirling Engine Build

Post by rmac »

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.
Progress Report #9:

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

displacer_ends.png
User avatar
NP317
Posts: 4557
Joined: Tue Jun 24, 2014 2:57 pm
Location: Northern Oregon, USA

Re: Moriya Stirling Engine Build

Post by NP317 »

Well done.
RussN
User avatar
rmac
Posts: 787
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Moriya Stirling Engine Build

Post by rmac »

NP317 wrote: Tue Mar 16, 2021 11:20 pm Well done.
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
User avatar
rmac
Posts: 787
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Moriya Stirling Engine Build

Post by rmac »

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

gaskets.jpg
Wolfgang
Posts: 184
Joined: Fri Jul 03, 2015 9:47 am
Location: S-W Ontario
Contact:

Re: Moriya Stirling Engine Build

Post by Wolfgang »

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
User avatar
NP317
Posts: 4557
Joined: Tue Jun 24, 2014 2:57 pm
Location: Northern Oregon, USA

Re: Moriya Stirling Engine Build

Post by NP317 »

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
User avatar
rmac
Posts: 787
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Moriya Stirling Engine Build

Post by rmac »

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
User avatar
rmac
Posts: 787
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Moriya Stirling Engine Build

Post by rmac »

NP317 wrote: Sun Mar 21, 2021 3:46 pm The teflon gaskets should work fine, as long as they don't compress and "flow" with clamping pressure. That would be my only concern.
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
User avatar
NP317
Posts: 4557
Joined: Tue Jun 24, 2014 2:57 pm
Location: Northern Oregon, USA

Re: Moriya Stirling Engine Build

Post by NP317 »

RMac:
"Cold flow."
I would suggest your operating temperatures are not "cold."
Just saying.
RussN
Post Reply