How to Make a Paint Can Stirling Engine
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This is the current project on Stirlingbuilder.com: The construction of a Stirling Engine from a paint can. As you can see in the video the prototype is up and running. It is not real fast, but it will run slow and steady like this for a very long time. It will run with or without ice on the top. The heat source is a liquid wax candle. The engine has had two long test runs that were each over an hour. Both times the test was stopped before the engine stopped on its own.
Using a paint can to make a Stirling Engine is not a bad idea. Empty paint cans can be purchased at most stores that sell paint. They are clean and shiny, and they are made of tin that is usually pretty easy to work with. The basic shape for the pressure chamber has already been formed. And they have a removable lid! This allows you to gain access to the interior of your pressure chamber before, during, and after all phases of construction.
The basic premise for this model is that we will shorten a paint can to be a little over an inch tall and use it as the pressure chamber. The flywheel is made from the lid of a second paint can. The body of the second paint can becomes the stand on which this Stirling engine sits. A liquid wax candle is used as the heat source.
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Paint Can Stirling Engine Parts List
1-gallon paint cans (2)
15 oz. bean can
35 mm film can and lid
Wire coat hanger
3/16” poster board
RTV High Temp Silicone
5 minute epoxy
1/16” music wire
UHMW Plastic Jig Stock
3/8” O.D. x 3/4” threaded lamp tube (pipe nipple)
3/8” hex nuts
Finding the Parts
I purchased the paint cans for about $4 each from a local hardware store, in the paint department. You may have to ask where they are in the store, but most stores that sell paint also sell the empty cans. I strongly recommend that you buy new cans that have never held paint. The bottom of the can is going to be exposed to a flame and we don’t want to have any problems with fumes or smoke from burning paint!
The tin can that holds the drive mechanism was originally a can of Nalley’s Chili. The 15 oz. can seems to be a common size for soup and beans. It measures about 4 3/8” tall and is about 3” in diameter.
The 35 mm film can and lid were obtained by begging. I went to a one hour film processor and asked if they had any film cans they wanted to recycle. They gave me a handful for free.
The wire coat hanger came from the front coat closet. Don’t tell my wife. I had to reorganize a little bit. If you have several hangers, pick one that is nice and straight with a smooth surface. You are going to bend this into a pretzel, but it seems to work best if you start with a nice straight one.
The poster board can be purchased at a craft store or from an office supply store. This is foam core poster board with a paper surface on both sides.
The craft wire is used to create the connecting rods for the displacer and the drive piston. It is relatively soft and easy to work with. It is not a coated wire. It is used for things like flower arrangements.
The vinyl glove can be purchased in a pack of 10 pairs from the paint store for about $3. It is important that the glove be made of vinyl and not nitrile or latex. The vinyl can be heated and formed into the shape we need by using a simple thermoforming process. The other materials do not work in the thermoforming process.
The RTV High Temp Silicone is found at the auto parts store. It is used for making automotive gaskets. It is the best silicone adhesive I have ever used. It bonds well, it resists high temperatures, and it lasts a long time in the tube.
The 5 minute epoxy is the same stuff you can buy at just about any hardware store. I have two recommendations when it comes to buying epoxy. Avoid buying the dual syringe dispenser. These look real good in the store, but they are very hard to control when you are mixing small amounts. Also, look for glue that reaches its full strength in about an hour. There is no advantage to buying 5 minute epoxy if it takes 24 hours to reach full strength.
The music wire comes from the hobby shop. It is used in model airplanes for making pushrods. It is very stiff, very straight, and has a nice polished surface. It is perfect for the pushrod that passes through the pressure chamber top and moves displacer.
I purchased the UHMW Plastic Jig Stock from Rockler (http://www.rockler.com). The piece I purchased was 4” x 24” x 3/8”. It cost just over $20 and will provide enough material to make about 96 displacer glands. This stuff is perfect for this application. It is very slippery stuff. It is easy to cut and easy to drill. I use it to make the displacer gland for the top of the pressure chamber. The displacer pushrod will pass through a hole in the UHMW plastic and will move with very little friction. If you wanted to get creative you could make some good bearings with this stuff too.
The threaded lamp tube is a small length of brass tube that is used to hold a standard light fixture together. As part of a lamp, it holds the electrical fixture with its threads, and the electrical wires pass through the tube. In this engine it is used to secure the film can to the top of the pressure chamber. It allows an air tight seal and lets air pass in and out of the drive cylinder. You can find a 3/8" diameter, 3/4” long piece of this threaded tube in hardware stores that sell parts for light fixtures. They cost about $0.39 each.