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A few weeks ago Gareth had asked me to check out an article from an upcoming issue of MAKE. It was the Teacup Stirling Engine from Volume 17. Recently, I made the Gakken Stirling Engine Kit from the Maker Shed, which was really cool. However, I have never made one from scratch, and this was my opportunity to give it a try.
I'm not going to go over every last detail of the build since it is really well documented in MAKE, Volume 17 and you can even check out the digital edition here.
It's a fairly finicky machine, but as you can see, it really does run, and it runs well. It's a great project to try and tackle over the weekend.
Here are a few highlights from my build. I followed the instructions from the magazine and it ran great. I did make a few changes, but you don't have to for it to work. I just like to experiment. If you have any questions, leave them in the comments and I will respond. Thanks!
Casting the piston:
When casting the piston make sure you have a non-stick, flat surface. I used the plastic CD shield that came with my spindle of CDR's. You could easily use an old CD too. Cover the CD with parchment paper, that way the epoxy will not stick. I cast a few different pistons. I ended up using the one that I cast with JB Kwik Weld.
Making the Displacer:
I used the same technique as described in the article to cut the CD spindle down to size. It's just a standard cutoff wheel mounted in a drill press. It worked great.
Later, I used a small file to make the edges really smooth.
When marking the Aluminum plate for the displacer, use a Sharpie marker to make your scribed lines easier to see.
I used a jigsaw with a metal cutting blade to cut the circles. It makes the job really easy!
I added some plastic screws to the displacer ring. I did this to allow for easer adjustment of the displacer ring during assembly. You don't need to add these plastic bolts, but it makes gluing the plastic displacer ring really easy.
I didn't have a hole saw the right size to cut the opening for the piston. It's not a problem. Just drill a series of holes around your scribed line and use a file to smooth out the circle. Aluminum is really soft, so the filing goes very quickly.
Building the crankshaft:
The crankshaft on my Stirling engine was offset a lot less than described in the directions. It says to offset the piston by 0.15" - 0.20", mine was about 0.15". However, the displacer was suppose to be a little "less than 0.25" and mine is actually only slightly more than the piston at 0.15", in fact they really are the same offset. I think every engine will be slightly different depending on the construction.
More:
In the Maker Shed: Gakken Stirling engine kit
Great job on this, Marc. I know how hard this project is to realize and your build looks amazing.
One thing I wanted to point out to makers who decide to take a crack at this: The plastic stand-off/bolts that Marc uses -- similar to the metal versions seen in the "glamor shots" in the project in Volume 17 -- are only recommended if you use plastic/nylon, material that does not conduct heat between the two plates. You want the temperature differential between the bottom (hot) plate and the top (cold) plate to be as great as possible. You don't want to use anything that's going to transfer a significant amount of heat from one plate to the other. But as Marc points out, using these bolts does make assembly and adjustment of the displacer chamber easier.
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