Use RTV silicone, the pipe nipple, and the hex nuts to attach the film can to the paint can lid. Place enough silicone around the hole to provide an air tight seal. Set the hex nut on the inside of the lid so that very little (as little as possible) of the tube protrudes into the pressure chamber. It is OK if a little extra tube protrudes into the film can. But you want to maintain as much clearance for the displacer as you can.
Make and Attach the Crank Shaft Tower
Open a can of chili.
Heat and serve the chili. Now get
back to work on the engine. Wash out the
can and remove the bottom of the can with a can opener.
Drill or punch two holes near the top of the can. These will be your crank shaft bearings. The holes should be about 1/64” larger than
the diameter of your coat hanger wire.
The holes need to be as even as possible so that the crank shaft is
level when mounted.
Cut access holes in the front and back of the can. The access holes are about 2” wide and about
3 1/4” tall.
The chili can is mounted to the top of the pressure chamber
lid with small metal brackets and 5 minute epoxy. Cut some small scraps of tin from the paint
can scraps and bend them to 90 degrees and use them to brace the can in place.
The can needs to be aligned so that it is centered over the
gland. The crank shaft needs to be
centered over the drive cylinder. Place
a piece of straight coat hanger wire in the bearing holes so that you can
easily check the alignment as you glue the chili can in place.
Make a Shaped Drive Diaphragm from the Vinyl Glove
Thermoforming allows you to create a flexible vinyl
diaphragm that is shaped perfectly to fit the drive cylinder (film can) and the
piston assembly. This makes for a very
efficient drive mechanism that is free of leaks and offers very little
Create a small vacuum table by drilling some 1/8” holes in a
thin piece of wood and attaching a vacuum cleaner hose. It doesn’t have to be fancy. It just has to be big enough to support the
pieces for this project.
Cut a film can to create a tube that is 3/4 inches
long. This will be the “form” for the
Cut a vinyl glove to create a flat sheet of vinyl
fabric. Stretch the vinyl over a frame
to hold it flat for the thermoforming process.
In the illustrations here the vinyl is held on the end of an empty roll
of masking tape.
Place the form upright on the vacuum table and switch on the
vacuum. Use a heat gun or a hot hair
dryer to warm the vinyl fabric. When the
fabric becomes relaxed and smooth it is ready to be pressed over the form. Press it down onto the form and allow the
vacuum to pull it to the shape of the form.
Remove the heat. Allow 10 to 20
seconds for the vinyl to cool and then switch off the vacuum. Remove the vinyl from the form and trim off
the excess material.
The piston is made from two flat disks cut from a disposable
coffee cup lid. Use a quarter to trace
two circles on the lid and carefully cut them out with scissors. Mark the center of each disk and drill a hole
to fit a #4-40 x 1” bolt.
Place one disk on the inside of the shaped diaphragm, and
place the other on the outside. Place a
small drop of silicone between the plastic disks and the vinyl. Use a sharp object to carefully pierce the
vinyl at the center of the disks. Pass
the #4-40 x 1” bolt through the outside disk, through the vinyl, and through
the inside disk. Thread a bolt onto the
shaft and hand tighten it to hold the piston assembly and diaphragm
together. Place two more nuts on the
bolt and set it aside until the glue cures.
Make the Crank Shaft
Cut a piece of straight coat hanger wire so that it is 7”
long. The first crank will be over the
center of the engine and will lift the displacer. The second crank will be over the drive
cylinder and will be connected to the drive piston. The two crank sections are
offset by 90 degrees. As the crankshaft
rotates the second crank is following 90 degrees behind the first crank.
The first crank allows the displacer to move to within 1/16”
of the pressure chamber top and bottom.
If your paint can went together like this one, there will be about 3/4”
of travel available to the displacer.
But you should measure to be sure.
The formula for determining the size of the offset for the first crank
is: Offset=(DT-1/8”)/2 where DT =
Displacer Travel. So if your displacer
travel is 3/4” it would look like this: Offset=(3/4”-1/8”)/2. The answer in this case is 5/16”. The first crank must be 5/16” from the
centerline of the crank shaft.
The second crank over the drive piston will have a 1/8”
offset, which means the drive piston will have a total traveling distance of
1/4”. Remember that there is a 90 degree
offset between the two cranks.
Draw two parallel lines on a sheet of paper that are the
same distance apart as the offset for the displacer crank. Use these lines as a guide in bending the
coat hanger wire. Work with diligence to
insure that all sections of the crankshaft are parallel and true.
Draw two parallel lines on a sheet of paper that are 1/8”
apart. Use these as a guide for bending
the section of the crank shaft that attaches to the drive piston. Remember that there is a 90 degree offset
between the two crank sections, and that each segment must remain straight and
true to help prevent friction and wobble.
Install the bent crank shaft in place on the chili can.
Make and Attach the Flywheel
Use sandpaper to remove the non-stick coating from the
inside center of a paint can lid. Use
epoxy to glue a small block of wood to this bare spot in the center. After the glue cures you can carefully drill
a hole in the wood. (Use the compass
again to find the center of the flywheel.)
This hole should be a snug fit for the coat hanger wire. Attach the flywheel to the end of the crank