A Simple Stirling

[PaulR]

Actually you don't need a particular tap and die size, could be metric, could be Imperial, as long as it's smaller than the rod stock you are going to use. Just turn it down for the portion inside the displacer to the major diameter of the size you have.

Only the very end of the displacer rod actually needs to be threaded -- the rest of the interior portion can be smooth (the major diameter of your thread). If you then widen it to your stock size where it will butt against your lower cap on the outside, you can screw it into place from outside the displacer, and there will be relatively good sealing at both ends and a secure attachment. A wipe of a suitable compound (maybe muffler patch cement) before screwing tight will complete the job

Yes I understand what you mean but 3mm is the smallest tap/die I have at present. I was planning to use 3mm rod to keep the weight down rather than go up to a larger diameter then turn down the length inside the displacer. Looks like I need to spend some more money.

[PaulR]

Other options I was considering as per this image:

Top - threaded rod into boss at bottom end of displacer, with thin nut to help seal
Bottom - this method seems to be used in some of the toy engines, with a grub screw (black) securing the rod

I suppose both of these save weight by shortening rod and at least put the heavier end nearest the displacer cylinder bush

[Jasonb]

I've used both methods though as my displacers were larger I soldered in the thicker top piece which had also been lightened. First had two grub screws from opposite side, second tapped hole for a threaded rod with in my case a hex shoulder but a nut would do the same.

The only thing to watch with a horizontal is the displacer piston can sag so just run the rod right through and nut or grubscrew the far end.

[Dave Otto]

One other option would be to run the rod clear through the piston, this is the way Paul Jacobs designed the displacer pistons for the 1/2 size Lake Breeze fans. I have made two of them this way and they worked just fine.

Dave

[PaulR]

Thanks yet again for these tips, much appreciated! Once I've worked out how to attach the displacer cylinder and its bush to the 'frame' I'll get started.

[Dave Otto]

On the Cole's Hot Air Betsy, both the power and displacer cylinders are threaded into the Cylinder Block and sealed with gaskets. That would be quite a bit of work but might be an option.

Dave

[PaulR]

Thanks Dave. I'd have to fit a smaller end to the displacer cylinder as I don't have the equipment to thread a tube that size. I think I'm going to solder a square flange a few mm from the end and screw it to the frame, probably with the brass bush held by the same studding like the red parts in this image.

[Minh Thanh]

Other options I was considering as per this image:

Top - threaded rod into boss at bottom end of displacer, with thin nut to help seal
Bottom - this method seems to be used in some of the toy engines, with a grub screw (black) securing the rod

I suppose both of these save weight by shortening rod and at least put the heavier end nearest the displacer cylinder bush

 I did the same as you but mine is a little different in method 1 - because my stirling engine is quite small (6 and 8 mm power piston diameter) so I made it as light as possible

[PaulR]

I did the same as you but mine is a little different in method 1 - because my stirling engine is quite small (6 and 8 mm power piston diameter) so I made it as light as possible

Another good idea - thanks! 

[PaulR]

I've come up with a slightly different way of attaching the displacer rod bush, sandwiching it between the displacer cylinder and the frame, although that would mean an external connecting tube to the power cylinder. Bottom part of image shows back view (from displacer side).

I guess it's ok for the displacer to travel further to the right than the connecting pipe, it's not like a valve after all?

[uuu]

Your power cylinder shows some space on the left.  Clearly the piston won't get that far, or it would block the port.  So you could reduce that wasted space.

Wilf

[Jasonb]

Yes, no problem with the displacer going passed the link pipe. As Wilf says loose the dead space at the bottom of the power cylinder

[PaulR]

Your power cylinder shows some space on the left.  Clearly the piston won't get that far, or it would block the port.  So you could reduce that wasted space.

Wilf

Yes indeed, I only sketched in the power piston at the last minute to eradicate the dangling pipe 

[PaulR]

Yes, no problem with the displacer going passed the link pipe. As Wilf says loose the dead space at the bottom of the power cylinder