Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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I have lately been on a tear about spudguns, bows, slingshots, etc.
I have thought about building a spudgun, many times.
I finally got around to it...
First, here is a pic of my very first spudgun, ever.
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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Here is a closeup of "the works".
From left to right:
The grey pipe is from the sprinkler section. Yes, it is plastic.
The green thing is a modified sprinkler valve. I have modified it to open when I squeeze the blowgun, which you see hanging from it.
Next, I needed to drill and tap, to put the fill valve in there. I didn't want to do that in just a piece of pipe. Nor in a nipple. So, I made a fitting from two, 1" male adaptors and a short piece of 1" pipe. This way, when I drilled and tapped, I was drilling and tapping through about 2 and 1/4 of the amount of material, as compared to just a piece of pipe.
BTW, all of this is sch40 pvc, except for a few metal pieces, and the sprinkler valve.
The fill valve is simply a 1/4 male quick connect, a 3/8 to 1/4 adaptor, a 3/8 ball valve, another 3/8 to 1/4 adaptor, a 1/4 nipple, a 1/4 elbow, and another 1/4 nipple. (I like the looks of a 3/8 ball valve, in this configuration, better than the looks of a 1/4. AND they are cheaper. Even wih the adaptors counted in. LOL)
Next in line comes a 1-1/4" piston valve which I made, myself.
Below that is an elbow that goes to the comression chamber.
At the end, there are extra fittings for two purposes. One, I had to use the grey piece, to hold a piece of 1" pipe, in the right relation, to be the inside end of my "barrel". And the rest is simply fittings that I put in there, so that I can change the barrel. And so that I can dismantle the entire thing, for servicing.
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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The way this works is simple. Not as simple as the old soda can, lighter fluid tennis ball cannons, but still fairly simple.
You fill the cannon from your compressor, via the fill valve.
This fills up the compression chamber which is the lower of the two tubes.
The piston valve is a simple piston that is designed to slide in the tee fitting, until the rubber disk that is on it's nose, contacts and seals the back end of the barrel.
After that, the air from your compressor bypasses the piston to fill up the chamber.
The 1" sprinkler valve is mounted in such a way that it keeps the air pressure in. Until triggered.
You squeeze the blowgun. That lets what is called the pilot chamber, empty all it's air. Which allows the valve to pop open and release all the air on the piston side of the valve.
The blowgun is called a pilot valve.
The sprinkler valve, in turn, acts as a pilot valve, for the piston valve.
When the sprinkler valve dumps all the air from the pilot chamber for the piston, the piston is forced back. Unsealing the back of the barrel, and allowing all the air from the chamber to escape via that route.
It may seem redundant to use the sprinkler valve as a pilot valve, and use the blowgun as a pilot valve for the sprinkler.
The reason it is used in this build is becaise the sprinkler valve will dump the pilot chamber for the piston valve, a LOT faster than I could dump it, just using the blowgun. But the blowgun empties the pilot chamber for the sprinkler valve, adequately.
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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To build this, I had to modify a sprinkler valve.
And I had to build my own piston valve.
I didn't take any pictures of how I modded the sprinkler valve.
But there are pics all over the web, that explain this.
I may come back to this, later, to explain how the sprinkler valve is modified.
The piston valve...
If you look at a tee fitting, from the side... One side will be the barrel, and the other side will house the 'piston'.
I have already explained how this is supposed to work.
Now I will show some basics of how I built mine.
Here is a pic of the parts used. (Ignore the second coupling that I have placed a green "X" on. It wasn't used.)
You want the piston to fit your tube snugly. But not too snug.
You want a mass of air to push it one way or the other, easily.
But you want the air to easily leak around it, once it has sealed the barrel.
I found that 3/4" fittings make exactly the right fit inside a 1-1/4" pipe.
The parts should be fairly self-explanatory.
The cap is put on the end of a piece of 3/4" pipe.
The coupling is hogged out, so that it will slide over the 3/4". (Note, you don't really have to do this. Just cut the pipe to the right length to where the fittings snug up to each other when you glue them on.)
Drill a pilot hole in the nose of the cap.
Stack the wahers and the rubber disk, in the order shown.
The washer closest to the cap does the job of 'centering' the rest of them, on the nose of the cap.
I put some marine goop on the threads of the screw, before I screwed it in.
I cut the rubber disk to a size that is not quite the same as the OD of a 1-1/4" pipe.
This disk will have to seal against the end of a 1" pipe. But for service, it has to be able to be pulled out.
Cut it the same size at the 1-1/4 pipe, and it becomes almost impossible to pull out.
Cut it the size of the ID of the 1-1/4 pipe, and it doesn't seal the 1 inch barrel as well.
The compromise size gives me a good seal, and yet allows me to pull the piston out of the valve, backward.
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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This is a pic of the completed piston, and the 1-1/4 inch fitting and pipe it will be placed in.
Now, two things to note at this point.
The smaller the volume of air in your pilot chamber, that faster your piston will react.
And, the lighter the piston, the better. (To a point. You don't want something feather-light, either) The piston slaps the back of the pilot chamber, when it opens. If you have a heavy piston, it will eventually beat through the back end of that chamber.
You want to build the 'chamber' for the piston in such a way as to eliminate as much of the pilot volume as possible.
But you also have to let the piston travel far enough to do it's work.
The rule of thumb for travel is that the piston moves back at least a distance that is 1/4 of the diameter of the pipe it is sealing.
I made mine travel farther. But there is a point where letting it travel further back is not really adding anything to the performance. So, I settled on what is probably 5/8 of the diameter of the pipe.
With all this in mind, you lay the piston next to the assembled pipe and fitting that will make the chamber, and mark on the pipe, the approximate 'travel of the piston.
This will give you a rough idea of where to cut the pipe that will comprise the piston chamber.
Now, one other thing that I have done, that most do not, is that when the piston slaps back...
The same piece of rubber that was sealing the end of the barrel, now seals the forward face of the pilot chamber.
Ensuring that all the captive air has only one direction to flow. Out the barrel.
I put a bumper at the back of the pilot chamber, to catch that 'slap', when the piston comes back.
The bumper is made of two layers of the same rubber that the barrel seal is made of, with a piece of kneepad type of rubber sandwiched between them.
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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This is the completed piston, and a dry fitting of the piston chamber.
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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This is the completed valve assembly.
The piston is pushed up against the end of the barrel.
The barrel is on the left.
If you can envision it, the piston is in the chamber at the right.
There is a small gap behind it.
Then the bumpers. Which are backed up by a steel washer.
Then the threaded insert.
Note, if you attempt this, it is essential that you get a good seal on that barrel.
You have to carefully prepare the end of the barrel, or there will be a leak, there.
I laid pieces of sandpaper on the bench, stood the pipe on end, and carefully sanded, to make sure it was completely flat and square.
I went through three grades of sandpaper.
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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This is a gif of the piston in the open and closed postion.
Looks almost pornographic.
I guess you could call this spudgun porn. LOL
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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And finally, here are a couple of projectiles I have made for it.
The top one is 3/4" pipe and fittings.
I have more than half of the back end of that stuffed with foam.
Then there are washers filling the remainder of that space.
The bolt goes all the way through, and more washers are stacked on the front, before the nut.
The lower one is a piece of 1" pipe.
With enough foam stuffed in there, to hold the 5/16 lag bolt in.
I have fired this spudgun already with a "D" battery. And with some medicine bottles.
The medicine bottles being almost no weight at all, tumble all over the place, and come to the ground very quickly.
The "D" battery flew a flat trajectory for approximately 60 feet, before it started to fall. Shot with the cannon pointed flat straight ahead.
The medicine bottles wouldn't have gone as far as they did, if they hadn't sealed the barrel so efficiently. They are a very snug fit. So they ended up haivng more force applied to them, than the battery did.
The battery is a fairly loose fit. A lot og the force escaped around the battery. If I wrapped some tape around the end of the battery for a more snug fit, I would expect a longer trajectory.
Maybe today, but most likely tomorrow or later, I will go out and test shoot my two homemade 'loads'.
I don't have one of those cheap monitors that will tell how fast the projectiles go. Nor do I have a video camera. So I can't give any of that sort of 'damage report'.
But I will try to remember to take pictures of the damage these things do to a piece of plywood.
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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calvin
Reged: Apr 29 2002
Posts: 2390
Loc: NW Ohio
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I take it the thing didn't explode and you are now a statistic?
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Remodeling Contractor just outside the Glass City
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markcadioli
Reged: Apr 25 2002
Posts: 1406
Loc: Australia
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I think he should take up Plumbing as a trade.
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calvin
Reged: Apr 29 2002
Posts: 2390
Loc: NW Ohio
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Good possibility.
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Remodeling Contractor just outside the Glass City
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Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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No explosions.
The power was out, here, for a few days.
~~~
I took it apart.
I needed the sprinkler valve, to test a smaller one with. I can't afford to go get another sprinkler valve.
I've been building these with parts I already have. Well, mostly.
I have only had to buy a few fittings, so far.
I have built two others, already, and taken them apart. Had I had to buy all the materials necessary for the spudguns, and all the 'testing', dinking around, and just plain trying to build homemade versions of things that would otherwise be very costly... I would probably have nearly 300 dollars into this already.
As it is... not counting the parts I already had, I have spent probably no more than 35 dollars over a couple months.
I'd like to be able to sell some of these. But I have to get the build down to as simple as possible. Good power. And I have to make them look good. This is part and parcel to the reason I have been dinking around so much.
I think I am going to put the big one back together, tonight. With a bit of adjustment, to try to get a crisper response, and better velocity.
Tomorrow I'll shoot those two homemade ammo things at a piece of plywood. Then take pictures of the results. If the results are piss-poor, then I won't post the pics. LOL
I'm not going to build any more big ones. Unless someone wants one... LOL
The one I have been happiest with, so far... I built one around a 1/2" homemade piston valve. It's about the size of my 12ga pump shotgun.
I am going to Build a one inch valve, and then rebuild pretty much the same size and shape spudgun. (I'll attach a pic of the smaller one, which I already built around the 1/2" valve.)
When I have a suitable small one built, I'll also make darts for it. And possibly small arrows. Built right, and using the right 'ammo', these things can actually be used for hunting. Well, if you can figure out how it would fit in with your local hunting laws. LOL
But it is a ton of fun, just plinking at stuff, too. 
I think I'll keep better track of the build on the new small one, and start a thread on that one, as well. (Unless this is just boring the crap out of everyone.)
BTW: The way I build them, these things can go up to something like 220psi. But I am sticking with 100 to 125.
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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I never got the chance to fire the two projectiles.
It got too cold. The PVC gets brittle when it gets cold.
I might try with the smaller one, but only a shot or two at a time, then left in the house overnight, to warm up again.
Anyway, here are more pics of the half incher that works.
The parts are labeled here.
A: Chamber
B: Barrel
C: Piston chamber
D: 1/4" tee
E: Blowgun
F: Ball valve
G: Compressor quick connect.
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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In the last two posts for this thread, I will attempt to show how this works.
In this first picture...
The ball valve gets turned to the open position.
The compressor is connected via the male quick connector.
As the air flow in, it pushes the piston up against the end of the barrel. That seals the barrel, and keeps the air from just blowing right on out the barrel.
The air continues to flow around the piston, until the chamber is brought up to pressure.
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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Luka
Reged: Apr 25 2002
Posts: 1401
Loc: The great NorthWet
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And now, in this last pic...
The ball valve gets closed. Then the air compressor disconnected.
Take aim.
Now when you squeeze the blowgun trigger, all the air is evacuated from behind the piston.
Now there is a major pressure imbalance. None behind the piston, and 100 pounds of pressure or more, in front of it.
This slams the piston back.
Unsealing the barrel.
And all the air pressure in the chamber tries to get out the barrel, at once.
I had some problems getting the half incher to work with only the blowgun for a pilot valve, but finally tracked that down to the piston not being a tight enough fit in the bore.
It fired just fine, if I used the sprinkler valve. But I wanted to make it work without the expense of the sprinkler valve.
The problem was too much air leaking back past the piston.
Using the sprinkler valve, the volume of air behind the piston was dumped fast enough. With only the blowgun, that volume didn't empty fast enough. The leakage around the piston was too much. The piston didn't move because the pressure equalised too quickly from the chamber to the back of the piston.
Once I achieved a tighter fit of the piston in it's bore, the blowgun evacuated the pilot chamber fast enough, to activate the piston.
One of these days I'll make some blowgun darts from nails and plastic milk jugs, and try them out.
Another option for this one is to 'sabot' some 3/8" steel hunting shot, with tissue paper, and shoot that.
I'll probably try both out.
As well as sabotting some standard BB's, and making essentially a "shotgun" load.
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The true measure of a man is how he treats someone who can do him absolutely no good. ~Samuel Johnson
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