After attempting to print more air-tight pistons, I realized a flaw: I had changed the piston multitudes of times, and then printed all the different versions once over a series of trials!

Oops. So that means I don’t know which dimensions are air tight?

… Yes.

That meant experimenting more! I definitely had a better idea of what dimensions worked, but, er, that took a while.

After successfully printing a air-tight piston, I now had to face an even bigger issue.

See, the beta stirling engine actually has overlapping pistons, meaning one rod goes through another. This is pretty easy to design; just make a whole for the piston rod to slide through. But the big question is how I’d make this airtight. The solution was a tiny o-ring at the opening of the aforementioned hole.

This took quite a while to perfect. I needed the o-ring to compress a bit, while not being too hard for the rod to pass through.

The solutions:

1. Make the end of the rod rounded; sharp edges don’t transition smoothly.
2. Glue the o-ring so that its hole is slightly smaller than the rod diameter.

I also printed out the base with some adjustments:

1. The cylinder is separated from the base so that it can be printed more precisely.
2. The base is cut down to use less filament.
3. The screw holes are smaller to actually be compatible with my screws.

(I’ve done it again! I’ve went over the 10 hour limit TT-TT)