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My First Pneumatic Cannon

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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My First Pneumatic Cannon

Unread postAuthor: MarkV » Mon Jun 30, 2008 10:33 am

Howdy,

I am a new member here and have just finished my first pneumatic gun. I am showing it to the folks here at the forum and see what you think. Here it is:

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My cannon is a replica of the M1916 37mm Infantry Cannon. Here are a couple of photos of the real thing:

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For those who aren’t familiar with the M1916 37mm Infantry Cannon, it was developed by the French during WWI as an infantry support gun. It was basically a simplified ½ scale copy of their famous French 75mm cannon. It was quite successful in providing direct fire support in front line use and was adopted by the US Army upon America’s entry into WWI. Its success, along with its small size led to its use in the Renault FT-17 tank and many other similar tanks and armored cars built during and immediately after WWI. Its last recorded use in combat by the United States though, was in its original configuration as an infantry support field piece. They were used in May of 1942 by the US Marines to combat invading Japanese forces at Corregidor in the Philippines.

I took a number of liberties with it to keep the price down by using off-the-shelf components and things I had laying around the garage.

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Here are the basic specs:
NOTE: All of the PVC is schedule 40 pressure rated or better – with the exception of the SDR-21 barrel which is sleeved inside of a schedule 80 outer barrel.
ALSO NOTE: These are NOT instructions for making one of these guns. There are many critical construction techniques/details that are not covered in this description. I learned how to make it by reading everything I could come across on the spudfiles.com forum. I am posting this only to promote discussion and for entertainment purposes. If you want to build one, I suggest you read everything at spudfiles.com to figure out exactly how. CHECK YOUR LOCAL LAWS TO MAKE SURE IT IS LEGAL FIRST AND DO NOT BLAME ME IF YOU SCREW UP!

Barrel - 2" schedule 80 PVC outer barrel with 1.5" SDR-21 inner barrel sleeved inside. It has the bore needed to fire golf balls (which, coincidentally, are close to the actual gun’s bore size) combined with the strength of the heavy-duty schedule 80 outer barrel.

Valve/Trigger - 1" sprinkler valve. I modified the valve and installed the trigger as per the instructions I found here on this forum

Breech - The breech is a 2" schedule 40 ball valve - pressure rated.

Air chamber - The air chamber is 2" steel pipe with a 2" to 1" reducer at the back end which fits to the valve via a 1" steel nipple. At the front end there is a 2" to 1/2" reducer into which there is inserted a brass manifold complete with pressure gauge, pop-off safety valve (set for 135 psi), standard tire/schrader valve, and an air line quick connect. This handy little assembly allows me to pressurize the gun from either a compressor or a hand pump, provides a gauge that allows me to set consistent pressures for better accuracy, and has a relief valve to prevent over filling.

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Carriage - Like in the real gun, the carriage is made in two pieces that can be separated into a tripod and the wheels/axel assembly. The two main legs of the tripod are cut from a 2x6. The front leg is a piece of 1" pipe with a rubber chair-foot on it. The pipe-hinge where the legs all come together was made by cutting down three "Kwik Key" type pipe fittings. The wagon wheels are "landscape decor". They are really too weak for normal use but are a lot less costly than real wheels and are OK as long as you are careful with them. I made the axel from some scraps that I had in the garage - as result, the wheel track is about 5" narrower than on the real thing. Hopefully it isn't too noticeable. Someday I might pony-up for real wheels and a correct axel assembly.

Also like the original, my gun has a fully functional scope on it. The gun is mounted to the carriage via a swivel that allows it to be aimed up-down and left-right without having to move the carriage itself.

I have test fired the gun up to 50 psi in my garage with either balled-up paper towels or ping-pong balls as rounds and it appears to work fine. At 50 PSI it makes a loud POP/THUD sound that is very gun-like. The paper towel ball flies out faster that can be seen until it unwraps itself and quickly decelerates about 20 feet down the range (a.k.a. my driveway). Ping-pong balls are noticeably smaller in diameter than the barrel’s bore, which is sized for golf balls, so there is bound to be quite a bit of blow-by in the barrel. Ping-pong balls travel out horizontally for about 10 yards before they slow down. I have fired one golf ball at about 20 psi and it traveled about 5 yards before hitting the ground, bouncing several times, and ending up in the neighbor’s front yard across the street. So far I have been reluctant to fire an actual golf ball at anything like a decent psi due to the close confines of my neighborhood – I need a real test range!

I think I might wheel the cannon out into the street on the Fourth of July and shoot a few confetti canister rounds to impress the neighbors. These can be made using colored paper, a paper shredder, and the cardboard cylinder from old toilet paper or paper towel rolls - which coincidentally measure about the same as the bore. It might be a fun way to get around the burn-bans and anti-fireworks rules this year.

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What do you think?

PS - One technical question: After I got it all together, test fired it several times up to 50 PSI, and painted it, I noticed that I didn't reinstall the sprinkler valve's, spring when I took it apart to modify it. There are no signs of any leaks, internal or external, and the operation of the trigger/valve seems to be fine. I'd rather not take it apart again as it seems to be working. Do I need the spring?

MarkV
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Unread postAuthor: trollhameran » Mon Jun 30, 2008 10:48 am

that looks brilliant, alot better than my first cannon, well done. Hope to see some mroe like this :D
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Unread postAuthor: SpudFarm » Mon Jun 30, 2008 10:49 am

toss that sprinkler and PVC parts and make it a 500psi piston valve :D

anyway: that is one brilliant gun as said!
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Unread postAuthor: bigbob12345 » Mon Jun 30, 2008 10:52 am

Cool gun
But the sprinkler is working without the spring???what??
Ive never seen one seal without the spring before.
What brand is it? It looks like a typical watermaster.
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Unread postAuthor: pizlo » Mon Jun 30, 2008 11:04 am

Thats a really beauty. Great replica. And interesting breech design, even if it does have a lot of dead space. The sprinkler is a bit of a limitation, but ease of use makes it a good choice. Do you intend on painting the pipes?
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Unread postAuthor: homedepotpro » Mon Jun 30, 2008 11:23 am

great job. beautiful craftsmanship. well it seems odd but i can understand it working without the spring. you know what they say, "if it ain't broke don't fix it." I'd like to see a pick of it after paint.
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Unread postAuthor: Pilgrimman » Mon Jun 30, 2008 11:27 am

Well, it certainly seems like you've done your research! :cheers: That thing is very well constructed, and CLEAN! Hardly a primer stain in sight! If the sprinkler valve is working, leave it be, as I've had trouble with the solenoid screws sealing properly if I take apart/put together the valve too much. On a final note, if you want to shoot ping pong balls, 1 1/2" SCH-40 is an excellent fit! Welcome to Spudfiles!
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Unread postAuthor: Spuddin » Mon Jun 30, 2008 11:44 am

man im lovin it, so cool, breach load, pneumatic, portable, replica, what more could u ask for? i could shoot this all day long. are u planning on painting the whole gun. cant wait to see more guns u make...be sure to add it to the "cannons showcase" with a thumbnail pic.
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Unread postAuthor: Launch-Tek » Mon Jun 30, 2008 1:06 pm

Nice cannon! Welcome to spudfiles.
If this is your first I can't wait to see your next ones.
A nice piston valve could clean it up a bit.
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Unread postAuthor: Gippeto » Mon Jun 30, 2008 1:43 pm

Very nice! You really did your homework. :D

The only other thought I had was that you're (maybe) putting a lot of stress on the 1" fittings and sprinkler when firing.

I did notice that you have a wooden spacer between the barrel and chamber. Is your barrel secured at the front?
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Unread postAuthor: MarkV » Mon Jun 30, 2008 3:45 pm

Howdy again,

I have finished painting the gun since I took the photos that I posted. The first photo was taken during the painting process so the color of the carriage is the final color I used on the gun as well. Basically, I just painted the white PVC and the sprinkler valve. For the moment I'm leaving the steel pressure chamber/pipe and the sch 80 barrel in their natural gray as they look like gunmetal which helps complete the illusion.

I was cleaning up the garage after painting the gun and discovered the spring. I think it is the one from inside the sprinkler valve, but if you say that the spring has to be in there for the valve to work, then I am not so sure. All I know is that it appears to work now.

With regard to the dead space in the breech: Would it be better if, when I load it, I insert a "plug" in the back of the chamber to take up this space? I am looking for a way to keep the golf ball from rolling back over the hole where the air comes into the chamber, anyway. (For my test shots I have been putting a small tab made out of masking tape on the ball to keep it from rolling back. This works but makes for rather slow loading.) If I make a removable 1.5" diameter plug out of wood, it could take up the dead space behind the air inlet. This would also give me a place to put a stiff wire, sticking out of the face of the plug, that could keep the ball from rolling back over the hole. - What do you think?

I am curious to know more about the possiblity that I may be overstressing the 1" fittings and sprinkler valve. The nipple on the pressure chamber side of the valve is steel, all of the rest is schedule 40 PVC with what I hope are healthy PSI ratings marked on it. I intend to keep to a self-imposed limit of 100 PSI as a factor of safety. Is there a better way to construct this? By the way, the block is firmly held in there by friction at the moment. I was originally thinking about putting a large hose clamp on it, but it seems very stable as is.

If anyone could describe a piston valve assembly that could be made to fit the general appearance of the actual gun, let me know. Like I said, I am new to this, so I want to keep it simple.

MarkV
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Unread postAuthor: psycix » Mon Jun 30, 2008 4:02 pm

While I am not a huge fan of "old cannons", this is a very clean and nice build!
You can be proud of yourself of doing one heck of a nice job!
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Unread postAuthor: Spuddin » Mon Jun 30, 2008 4:06 pm

no no dont change a thing, u dont need a piston valve, the gun is perfect as it is. as for the ball rolling back maybe wrap it in some tape to make a tighter fit?
for them to say change it to a piston gun is like building a pneumatic cannon and say u should change it to a combustion, just dont make any sense.
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Unread postAuthor: Gippeto » Mon Jun 30, 2008 4:34 pm

What I was referring to was the following;

The recoil force acting on the barrel is on a "raised" plane relative to the sprinkler valve. This would make for a "bending" moment at the weakest point (the threads on the sprinkler valve).

While I'm certainly not SURE that this will exceed the limits of the materials involved, in my opinion it is still worth thinking about.

If you could secure the barrel to the chamber @ the wooden spacer, you would eliminate much if not all of the bending moment. Nullifying any problem here before it arrises.

A chamber sealing piston valve would "fit in" just right.

http://www.spudfiles.com/forums/piston- ... t8157.html

Just my .02
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Unread postAuthor: biged » Tue Jul 01, 2008 5:43 am

Very nice artillery piece. Great work!
It is nice to see another red-legs on the forum.

Where (and what size) were you able to procure the wheels from?

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