Picture of  Build a water mortar
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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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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l8nite3 years ago
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....
on the last picture, it the kid on the bike talking on a cell phone??
He's relaying the co-ordinates to the shooter!
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...

It's a bad habit none-the-less.
m32825 (author)  U.S.M.C.Demolitions7 years ago
That's mortar fire control talking to forward observers!
LOL.  Hilarious!
....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
Fire for Effect, I repeat Fire for Effect!!

No  he was putting his helmet on.

john15nlt4 years ago
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.

EmmettO4 years ago
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.
jediking145 years ago
Cool but i think I'll stick with "the tennis ball mortar"
ThePlumber7 years ago
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.
I've thought about doing this with 1/2" copper and 2L bottles, but the problem is finding suitable check valves for the repeating mod.
Boating supply shops have 1/2" non-return valves.
m32825 (author)  ThePlumber7 years ago
Good idea! How about hooking the hose up to a fitting near the top? Then you could let the water pressure do most of the filling. This is giving me more ideas that need to be tried... :)
hooking up a hose would make it like a piston kind of... maybe if you put just enough friction on the inner pipe, then it would go down only when water was put in it. then, there was a weight sensor below the pipe and could tell when it was full of water and then told a motor to push the pipe?
what is the range on this thing?
whats with good stuff ruined with pvc.where can you get that anyway
hopenui6 years ago
This is Awesome! Love it
DUDE i made one of these in PEN form and size that shoots powdered sugar! it has gotten me into no trouble and has annoyed other guys at my school to no end! tis awesome!
ROFL, did you take a screenshot of a guys avatar? Preferably a guy named AlphaCamo on deviantart?
Nope. For some reason, my GIF didn't work.
i would very much like to hear more about this. It sounds like it could be really fun to annoy people with !
i'd like to see a picture/instructable.
make an instructable of the powdered sugar version. it seems cool.
m32825 (author)  Lt. Duct Tape7 years ago
I've been focused on scaling up, but this is a reminder to think of applications at the other end of the size spectrum. Good work! Got a picture?
thinkahead7 years ago
Instead of the wooden plug why not just cap the other end?
m32825 (author)  thinkahead7 years ago
I looked at that a bit. The normal PVC end cap for the inner pipe won't fit into the outer pipe, it's too big. I've seen heavy duty pressure testing plugs, but they're about $10. There were some thin plastic disks in the pipe area that look like they could be glued in place at the end of the pipe, but I'm not sure how durable they'd be. The wooden plug is one of the centers used to turn the grooves, so in addition to being heavy-duty, it's convenient!
...maybe an illustration will make it more clear...
m32825 (author)  thinkahead7 years ago
Oh, I see. This would work if you stand the mortar on end, extend it all the way, then pour water into it to load. If you put the nozzle down into a bucket and draw water up, you'll have air in the inner pipe that will switch places with the water when you flip it to prepare for a shot. If you're drawing water up, it seems best for the inner pipe to have a piston-like top.
No different than a turkey baster... after squeezing and releasing the bulb the first time to suck up the first load you turn the opening up, squeeze the bulb again to expell the air. Next you place the opening back into the liquid and release the bulb again, or in this case retract the pipe again. Now you have a fully loaded mortor.
m32825 (author)  thinkahead7 years ago
I like it. You end up carrying around a couple extra pounds of water, but being able to use an off the shelf end cap is well worth it. Once you cap the inner pipe you could fill it with some of that expanding foam stuff to reduce/eliminate the space for unusable water.
When it comes to war the last thing you want is to run out of ammunition.
He needs a way to hook the hose into it for fast refills and unlimited ammo.
Use a nozzle so the water doesn't just run and waste water.

No, when it comes to war the last thing you want to do is die.
I know this comment is a little late, but...this is an updated image. If you look at step 8 there is a plug on the same side as the o-rings. When you fill it you are really only filling the larger diameter of pipe. The smaller diameter of pipe should always be full of air (unless you have a leak). They sell these things for like 2/$1.00 at $ stores. They're made of really cheap plastic. I must have had 20 of these things growing up as they break after only slight abuse. I'm sure the PVC holds up a lot better, good instructable!!
this isn't the best idea because u have a bigger volume of open space. And, it would only shoot the old amount of water.Pulling it apart and filling it up wouldn't work because it would only fill up 1/2 of the volume. but good instructable i will defiantly be making one
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