This water mortar is made from PVC using a variation on the "drill press lathe" technique from the book "Eccentric Cubicle." The finished product launches over a quart of water per shot!
Also see the followup instructable, with more design ideas...
Step 1: Parts
- 30" of 1 1/2" schedule 40 PVC
- 24" of 2" schedule 40 PVC
- End caps for 2" PVC
- Plumber's silicone lubricant
- 2 size 224 Buna-N O-rings
- 6 inches of 1"x3" oak
- 2 chunks of 2"x4" for pillow blocks
- 6" of 1/4"x20 threaded rod
- 4" long 1/4"x20 carriage bolt
- 1 1/2" long 1/4"x20 bolt
- 1/4"x20 nuts
Here are the tools you need:
- drill, twist bits, spade bits
- 1 3/4" hole saw (the kind that cuts out a plug)
- 2 bearings with shoulder bushings (from old inline skate)
- 2 clamps, mine were 8"
- dial caliper
You can get O-rings from Superior Seals, they have a great selection of sizes and materials.
Step 2: Make centers for the inside pipe
From this page's table for PVC pipe we see that 1 1/2" schedule 40 has an inside diameter of 1.592", so the plug left after cutting a 1.75" hole turns out to be just about the right size to fit the inside of the pipe. If you tighten the collar of the hole saw, you will get a larger plug, if you loosen it, you will get a smaller plug (because the bit wobbles). These piece should jam tightly into the ends of the 1 1/2" pipe, so it's best if they start out a little too big and you sand a little to taper the plug (use the 1/4"x20 bolt and nuts to chuck it into your drill and hold a sanding block up against it for even results). If your pieces are too small, build up their diameter by adding wraps of masking tape. Let the tape hang off the inner edge a bit so it can guide the pipe onto the center without being pushed back.
Once you've got the fit right, assemble the centers as shown below. The "driven" center is in the foreground, the "non-driven" center is in the background. Using spade bits, drill the 2"x4" chunks to make pillow blocks for the bearings.
Step 3: Set up for turning
The carriage bolt protruding from the driven center is chucked into the drill.
I haven't tried it, but the whole setup might be more solid with a single piece of 1/4"x20 threaded rod running from end to end.
Step 4: Mark grooves
Step 5: Turn grooves
Grooves should be flat-bottomed with smooth, squared-up sides, and enough width to give the O-ring some room to breathe.
Step 6: Check groove depth
Once the target diameter is reached, remove the pipe from the turning setup. Bevel the inside lip of the outer pipe so that the o-rings will slide into it easier. Clean everything before assembly. Put damp, folded pieces of paper towel over the end of the inner pipe and push them through the outer pipe to clean dust and debris out. Put both O-rings into their grooves, liberally lubricate everything, and check the fit.
Step 7: Prepare end plug
Step 8: Install end plug
Step 9: Check fit
Step 10: Prepare end cap
Step 11: Final assembly
You can remove the cap by tapping the opposite end of the inner pipe against the floor.
Step 12: Try it out
Bonus fun: if you pull the inner pipe back and seat an undrilled end cap, you can launch the end cap with pneumatic pressure, generating an impressive bang in the process. Make sure it's not aimed at anything or anyone. Also make sure you're not inside your garage when you discover how cool this is like, uh, someone I know was: a garage door makes a resounding boom when you nail it with an end cap!