Warning: It is specifically against manufacturer recommendations to use PVC to contain pressurized air. These instructions are to be used at your own risk.
Welcome to my attempt at building an anti-aircraft style coaxial PVC launcher. This launcher will be purposed for use in airsoft/military simulation games. The base cannon design was found on another site and I see that the creator also has an instructable posted here. Please feel free to follow or reference his instructions just be aware of my modifications to the firing and filling mechanisms.
(2) 3 inch slip coupling
(1) 3 inch x 2 inch reducer
(1) 2 inch slip x 1 inch female threaded reducer
(1) 3 inch x 2 inch flush reducer
(1) 3 inch slip to male thread adapter
(1) 3 inch slip to female thread adapter
(1) 3 foot section of 3 inch schedule 40 PVC piping
(1) 3 foot section of 2 inch schedule 40 PVC piping
(1) 3 foot section of 1.5 inch schedule 40 PVC piping
(1) 3 inch tank to bowl washer (for toilet)
(2) 3 inch steel gas vent T caps
(1) Rainbird 1 inch in-line sprinkler valve
(1) 3/8 inch hose barb to 1/4 inch threaded brass fitting
(2) 1/4 90 degree male to female brass fitting
(2) 1/4 hose barb to 1/4 threaded adapter brass fitting
(1) 1/4 inch brass schrader valve
(1) 160 PSI gauge with 1/4 inch bottom fitting
(3) 1 inch steel self-tapping screws
(1) Sheet of rubber
(2) Small screws
(1) 1.5 Feet of 6x2 cedar
(1) ~3 Feet of 1/4 air hose pressure rated to at least 200psi
(2) Small hose clamps for the air hose
(4) 5 inch pipe bands
(1) 4 inch pipe band
(*) Plastic bonding spray paint
(*) Teflon thread tape
(*) PVC Primer/Solvent
(*) PVC Cement
(*) Thread Paste w/ TFE
(1) Small hinge
(1) Small clasp
(*) Acrylic paint: Green, Yellow, Red
Masking or painters tape
Various drill bits
Step 1: Rear of Launcher Chamber
Lets get started on the rear of the launcher chamber. If you've never worked with solvent welding/PVC cementing please do some research or perhaps start with a simpler project for your first go. As always please use care to ensure proper ventilation when working with PVC solvent and cement.
PVC Solvent Welding quick tips:
a. Coat both pieces with the PVC primer, cover the areas where they will be joined.
b. Before the primer dries, coat the socket with a thin layer of cement.
c. Before the primer dries, coat the pipe or fitting that will be going into the socket
d. Apply another thin layer of cement to the socket.
e. Quicky join the pieces, try to rotate them a quarter turn as you join them to ensure a good seal.
f. Hold them togther snugly for about 30 seconds to prevent them from pushing out/apart
g. You can handle the parts after about an hour, takes about 8 hours to fully cure/dry in 50-80F, longer in colder temperatures
1. Weld the 3 inch to 2 inch reducer into one end of the 3 inch slip coupling.
2. Weld the 2 inch slip to 1 inch female thread reducer into the 2 inch slip opening.
Step 2: Prepare Flush Reducer
If your 3 inch to 2 inch flush reducer has a hex lip on the outer edge it needs to be ground flat since we will be using the reducer in the opposite direction.
Picture below shows the lip on mine mostly ground off. I used my bench grinder, you can use that or a sander or a file, although the latter two could take some time.
Step 3: Chamber and Barrel Preparation
1. Weld the 3 foot 3 inch chamber pipe to the 3 inch male thread adapter.
2. Weld the 3 foot 2 inch barrel pipe into the 3 inch to 2 inch flush reducer.
Step 4: Assembling the Chamber
Sorry for the bad picture, the instructable I linked to in the intro explains this part in detail.
1. Join the 3 inch female threaded adapter to the 3 inch x 2 inch flush reducer. I screwed the female threaded adapter onto the male threaded adapter to help me join it to the flush reducer. To possbily help explain, the 2 inch barrel we previously joined to the flush reducer is now running down the middle of the chamber in the picture. They can still be separated by unscrewing the threads.
Step 5: Build the Piston
1. Grind off the outer lip on both steel gas vent T caps.
2. Sand the inside of both T caps.
3. Sand the bottom of one T cap.
4. Epoxy the two caps together, the one with the sanded bottom goes on top. This will take a decent amount of epoxy 2-3 oz.
5. Let the epoxy set.
6. Cut a piece of rubber to fit inside the face of the top T cap and super glue it down.
7. After the super glue dries you can optionall add epoxy around the edges to hold it down.
8. Wrap the outside of the piston with layers of aluminum tape to create a better fit inside the chamber.
9. Be sure to place the piston into the chamber before sealing the chamber, and remember the front/rubber goes away from the bowl washer.
Step 6: Assembling the Rear of the Chamber
1. Place a 3 inch tank to bowl washer insde of the rear chamber we assembled earlier.
2. Weld the rear chamber to the chamber, 3 inch pipe to the open end of the 3 inch slip coupling.
Step 7: Preparing the Sprinkler Valve
Rainbird 1 inch inline valve
1. Disassemble the valve.
2. Cover the holes on the underside of the top with tape.
3. Seal all of the holes with epoxy.
4. When dry remove the tape. I added a little epoxy to the holes on the underside as well to ensure they were sealed. Allow all epoxy to dry.
5. Use a Dremel or hack saw to cut the solendoid and bleeder ports flush with the lid of the valve.
6. Drill a hole in the lid of the sprinkler valve, make sure its slightly smaller than a 1/4 inch 90 degree brass fitting.
7. Place a 3/8 barb to 1/4 thread adapter into the chuck of a 1/2 inch cordless drill. Place the drill in a low speed setting if possible and drive the adapter into the hole this will cut threads into the lid. Remove the 3/8 barb from the lid.
8. Using teflon tape to wrap the threads. Attach a brass 1/4 inch hose barb to 1/4 inch threaded adapter to a 1/4 inch 90 degree brass fitting.
9. Use a 1/4 inch drill bit to drill out the inside of the new 90 degree adapter (drill through the threads of the 1/4 inch barb adapter) to allow for better airflow.
10. Attach the new 90 degree fitting to the lid of the sprinkler valve, again using teflon tape to seal the threads. Point the hose barb straight away from the solenoid port. (even though my initial picture has it facing the solenoid port)
11. Replace the spring taken from the center inside the valve. Use a pliers to open one end of the spring up a little bit (increase its diameter) and fit it around the threads coming through the lid of the valve.
12. Drill holes for the schrader valve and PSI gauge, ensure that the holes stay below the inner diaphram ring (noted in the picture). (Same size as the hole made in the lid) (Also note the locations of the PSI gauge and schrader valve to the flow makrings)
13. Reassemble the sprinkler valve.
Step 8: Barrel Face Preparation
1. Sand the barrel face as smooth as possible to aid in sealing against the piston. I even put a little layer of clear coat spray paint over the face to help seal it.
2. Drill 3 tiny pilot holes equally spaced apart about an 1 inch from the barrel face.
3. Drive a 1 inch self tapping screw into each hole.
4. Adjust the screws to space the barrel so that it is center in the 3 inch chamber.
5. Put epoxy around the screws on the outside of the barrel to seal them since the outside of the barrel will be a wall of the air chamber (coaxial design).
These will also keep projectiles from contacting the piston face.
Step 9: Attach Barrel to Chamber
1. Coat the male threads with thread paste.
2. Use a pair of strap wrenches to thread the female adapter with the barrel into the male adapter with the chamber.
Step 10: Attach the Sprinkler Valve to the Cannon
1. Coat the 2 inch long 1 inch diameter nipple with the thread paste.
2. Screw the sprinkler valve to the rear of the cannon. (Ensure the flow of the valve is directed away from the cannon.
Step 11: Valve Shield & Exhaust Port
1. Cut a 3 inch slip coupling in half with a Dremel or like tool.
2. Sand the ledge around the rear of the cannon.
3. Epoxy half of the slip coupling to the ledge of the cannon.
4. Drill a small hole in rear of the valve opening.
5. Cut a piece of rubber to fit inside the threaded opening on the back of the sprinkler valve.*
6. Screw that rubber piece inside the valve.*
7. Repeat for a rubber flap on the outside of the valve opening.*
8. Cut the other half of the slip coupling to fit around the hose barb and schrader valve.
9. Attach it to the side of the epoxy'd half slip coupling with a small hinge.
10. Bend a claps to the angle of the coupling and attach it to the two halves of the coupling.
*Between the rubber flaps is where you can place powders to simulate a launch when the cannon is fired!
Step 12: Trigger Mechanism
1. Ensure there is a decent flow through the airgun (some chinese ones are crap)
2. Using a dremel cut off the finger guard and grind it flush.
3. Attach the 1/4 inch 90 degree brass fitting to the 1/4 brass hose barb adapter, be sure to use teflon tape on all of the threads.
4. Use a 1/4 drill bit to drill out the threads from the barb adapter that you can see inside the 90 degree fitting to increase airflow (same as the earlier fitting.
5. Attach the brass to the airgun, again use teflon tape on the threads.
6. Now push one end of the 1/4 air hose onto the trigger mechanism barb and secure it with a small hose clamp. Make sure the screw portion of the clamp is downward towards the airgun.
Step 13: Grips
These will involve some imagination and woodsmanship.
1. Cut a 7 inch piece of 6x2 cedar.
2. Fashion a desirable grip design, it helped to lay the airgun mechanism on the block of wood and draw around it.
3. Cut out the grip roughly with a jigsaw.
4. Using a 1/2 inch drill bit and the Dremel with a high speed cutting bit router out a space inside the grip for the trigger mechanism
5. Cut the grip section slightly thinner with a hacksaw
6. Use a Dremel sanding bit to create the finger grooves.
7. Sand it all to taste
I don't have any creation pictures of the front grip (there are some in the final assembly) but the same process was used minus the routering out for a trigger.
Step 14: Sight Mount
My design idea came from this site: http://blog.kotarak.net/2011_04_01_archive.html
I used 1/16 aluminum L bar for the outer frame and 1/8 aluminum bar for the hinge and mounting it to the cannon. The piece attached to the cannon simply has a slot cut in it for one of the pipe bands to pass through. The phone is a spare Droid 2 device I had around and the app I use is called Geo Cam there is both a free and paid version. The phone is velcroed to the mount. The hinge is a special bolt I found at Lowe's that has the knob on top and is a #10 bolt. I added a lock washer and two nuts. I put a small screw in the bar attached to the cannon then Dremel cut a small notch in the bar attached to the sight so that it stops the hinge straight open. I drilled a hole for the camera to see through.
Step 15: Mounting the Grips
Place them to your liking. Use trial and error to find what's most comfortable for you.
1. To mount them use a drill to create slots for the pipe bands to pass through. Be careful on the trigger grip to avoid the airgun and hose assembly. I used 5 inch pipe bands to secure the grips.
2. Cut the air hose to the necessary distance and mount it to the the sprinkler valve with the other small pipe band, ensure that it is taunt.
Be sure to tighten the pipe bands for the grips slowly as they get tight and make sure the wood does not start cracking.
Step 16: Air Line Shield
1. Cut a piece of 1.5 inch pvc piping vertically, not right down the middle but slightly off center so that one half is bigger than the other. I had to get creative with a compound miter saw to get the cut i needed.
2. The smaller rear pice is epoxy'd to the cannon.
3. I started off epoxying the large one and ended up putting a 4 inch pipe band to ensure it stayed secure.
Step 17: Cosmetics
Bullet Bill Decals