Build a Water Mortar




About: My name is Carl, I'm an engineer. I like to build things and solve problems. I like learning how other people build things and solve problems. I like to laugh, and look for the humor in any situation. I...

How to build a super-soaker-like toy from PVC.

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...

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Step 1: Parts

Here are the parts you need:

- 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"
- gouge
- 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

Use the hole saw to cut two plugs from the 1" oak.

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

Insert the centers into the ends of the pipe. Roll an O-ring over the pipe. Seat the bearings into the pillow blocks. Check to see that the pipe rotates smoothly. Firmly secure the pillow blocks.

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

Set the drill for a relatively low speed and lock it on. Use a permanent marker to mark positions for the grooves. The first one should be a little over 1" from the end, the second one should be about 4" further down the pipe.

Step 5: Turn Grooves

Start with the drill at a slow speed until you get the feel for things, then speed it up for faster cutting action. If you get too much wobble in the pipe, slow down. If you don't have a gouge, experiment with different sharp-edged objects held at about a 90 degree angle to the pipe. I used the bottom end of a round-file for my 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

Roll the O-ring into the groove and measure the outside diameter of the O-ring with a dial caliper. Rotate the pipe slightly and measure at a couple positions to get an average diameter. The average diameter needs to be about .010" bigger than the inside diameter of the large pipe. The table referenced earlier says the inside diameter of 2" schedule 40 PVC should be 2.049", but measure yours and add .010" to get your target diameter. If the O-ring fits too tightly, it will bind and not slide smoothly, if it is too loose, water will leak past it.

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

Use one of the centers to make an end plug. Insert a 1 1/2" long 1/4"x20 bolt, put a nut on the other end, tighten.

Step 8: Install End Plug

Work the end cap into the end of the inner pipe. The head of the bolt should be visible. Once it is started you can turn the pipe over and tap it against the floor to seat the plug tightly. If the plug is not tight enough it will get sucked out when you draw water into the chamber. You can use a wrap of electrical tape at the base of the plug to make it fit more snugly.

Step 9: Check Fit

This is what the end should look like when everything is together. Nice and even, with smooth motion.

Step 10: Prepare End Cap

Drill the end cap. A single 1/2" hole seems to work pretty good. Get a few end caps and experiment.

Step 11: Final Assembly

Place the end cap onto the outer pipe and seat it by tapping firmly on the floor.

You can remove the cap by tapping the opposite end of the inner pipe against the floor.

Step 12: Try It Out

Get a bucket of water, push the inner pipe all the way in, put the end cap under water, pull the inner pipe back until you can just see an o-ring, quickly tip the end cap skyward to keep leakage to a minimum, place the end of the inner pipe on the ground, tilt in the direction you want to fire, pull downwards on the outer pipe to fire.

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!

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    95 Discussions


    Answer 1 year ago

    I think they allow the pipe to be turned in steps 3 & 4.


    10 years ago on Introduction

    This is a very nice instructable. The thing that I like about water wars is that you don't have to buy pellets, you don't have to buy paintballs, you don't have to buy darts, you don't have to pick anything up, you don't even necessarily even need to buy a gun or super soaker (a full bucket of water works fine), and the ammunition you shoot someone with stays on them. Of course, the other types of war games are fun too, but water wars are so much easier to understand because all you have to do is get to soak the other person with water! You don't have to scrub any paint off, it's clean, it's safe, and its great for hot weather (winter no-no), and it's FUN! And now, water balloons (biodegradable) are used, and even-rockets are being used. Even mines, RC robots, vehicles, bases/forts, etc... are used in water wars. And it's so easy. Just add water (and pump) and shoot. (If anyone who is interested in this sort of stuff, then you might want to look at my group that is made specifically for water warriors like you-The Water Warrior Group.)

    1 reply

    8 years ago on Introduction

    I was looking over your parts list and I was looking over how you built this and I have to say, impressive but I might have a way to save a bunch of time.

    I used to build slurp guns to pull ghost crabs ouf of the sand at the beack to fish with. Its basiclly the same prinicple only in reverse. Instead of O rings, we built them with adjustable pressure plugs. Basicly its two metal washers with a rubber grommet in the middle. there is a hole in the middle with bolt through it with a wing nut attached. As you tighten the wing nut the rubber gets squeezed and it makes it bigger, which makes the seal tighter.

    Not my plans but I googled it and here is a similar thing someone else built using one of these pressure plugs.

    1 reply

    7 years ago on Introduction

    While re-reading this ible (because some day I'll make one for the grandkids) I saw the garage door comment and had to laugh. My younger brother who is still old enough to know better, recently froze paint balls and set up cardboard boxes as "targets" in front of his garage. The results were way more than he expected when the paint ball went through the box, and with a resounding CRACK BANG (or was it BANG CRACK?) through the garage door panel and dented his wifes BRAND new car....

    Whats wrong with that? jediking14 says he wasn't but if he was perhaps his dad was away on a business trip so his mum was letting him talk to him on the phone or something along those lines, its not illegal for young kids to talk on mobile phones or anything...


    Reply 8 years ago on Introduction

    It's a bad habit none-the-less.


    Reply 8 years ago on Introduction

    ....tkkkk....charlie team we need mortar fire 3 clicks north of our location and 2 clicks west, over....tkkkk....tkkkk....copy that bravo company, ready to fire on enemy position in 3....2....1.... mortars have been launched, over....tkkkk....tkkkk....bullseye charlie team, good shooting, thanks alot, over....tkkkk....tkkkk....anytime bravo company, over....tkkkk....tkkkk....over....tkkkk....tkkkk


    8 years ago on Introduction

    I finally got a chance to make a bunch of these. I made them with different sized nozzles (read: holes in the end of PVC cap) and then made one with three nozzles in different directions, just like those three way guns in the old side scroller video games.

    Tons of fun! Thanks.


    11 years ago on Introduction

    This is great... To make this better I would make it auto refill. Here's how... Add a one way valve to the side near the top and attach a hose that goes into a water bucket, or directly to the faucet. Then add a one way valve to the firing outlet. direction the valves so that when you push in the piston it fires and when you pull it out, it refills from the water source... UNLIMITED NON-STOP FIRING! This is just a mod of a simple pump mechanism, except this pumps water into other kids faces.