All pipe and fittings are schedule 40 PVC
1 1/2" pipe 72" long
3" pipe 36" long
1 1/2" to 3" bell reducer
3" female adapter
3" cleanout plug
Diaphragm (see below)
A couple old trouser legs
Source of compressed air
Blow gun with tapered nozzle (What's a blow gun?
It's a valve/nozzle combination that attaches to a compressed air hose.
They're commonly used in machine shops and
garages to blow dust away.
You can usually find one at most autoparts
Cut the pipes to length. The barrel pipe must
have a perfectly square and smooth surface on the breach end. You may have
to flat file and sand it to make sure a good seal with the diaphragm is
Cut a 3 3/16 diameter disk of 3/32 thick
polypropylene or polyethylene. A cheap dishpan from Kmart may be a good
source of diaphragm material.
The front bell reducer has a small ridge that
would prevent barrel from being pushed through it during assembly. Use a
half round file to remove the ridge. Make sure you can push the barrel
though the reducer. Remove the barrel and set it aside.
Drill a hole through the center of the cleanout
plug. Size this hole to achieve a tight fit with the tapered nozzle of the
Assemble the outer chamber first. Glue the bell reducer and the female
adapter to each end of the 3" pipe. allow the glue to dry before
proceeding to install the barrel.
Lace the diaphragm in the female adapter and
screw the cleanout plug in firmly. Push the barrel through the reducer until
it sets firmly against the diaphragm. Pull it back out 3 inches to allow
glue to be applied. Apply glue to the barrel in front of the reducer and
push it quickly back into position against the diaphragm. Hold the barrel in
place until the glue dries.
After the gun is assembled, remove the cleanout
plug and check to see if the barrel is properly centered in the female
adapter at the breach. If it is not, cut 3 or 4 pieces of 5/8" heater
hose about 1" long and force them between the barrel and the outer
Slip the old trouser legs over the chamber area
of the cannon and tape them in place. This simple precaution will contain
any pieces of exploding pipe from becoming shrapnel if something should go
To fire the cannon, unscrew the cleanout plug and
remove the diaphragm. Push a pre-cut spud into the breach of the barrel, making
sure it is an inch or two below flush. Replace the diaphragm and screw the
cleanout plug in firmly. Point the cannon down range. Place the blowgun in the
charging hole drilled centered in the cleanout plug. Start squirting air into
the cannon with the blowgun. When the sound of hissing air quiets down or stops,
the cannon is charged and ready to fire. Keep the blowgun valve pressed down.
Aim carefully and pull the blowgun from the charging hole.