SpudFiles

Hi Spudders!

Abstract:

I want to show you all my latest pneumatic cannon! Here's a brief overview. The valve is a piston type housed in a stainless 2" wye strainer fitting. The chamber is 2" sch40 stainless threaded pipe. The barrel is sch10 anodized aluminum pipe with 1.682" ID (golf balls!!!). The pilot is just a little blowgun and that's it! The stock is made from heat bending/shaping/cutting 1" PVC pipe and wrapping with bike inner tube. The max operating pressure for this cannon is 300psi (based on fatigue limit of weakest point on chamber with F.S. of ~1.5), but I have only tested to 200psi indoors dry fire. The overall weight of the gun with scope is about 13 pounds.

So for the details:

The Big Stainless!

I got these fittings shipped from China through ebay. The wye cost only $45. And it's good steel too. When I was drilling a hole in the endcap of the wye strainer, it took me 30 minutes with a cobalt drill bit, hand drill, all my weight, and lotsa WD-40. Very strong stuff. The wye is rated to 800 psi WOG. The weak point of the chamber is the thread roots 5/8" inches up the nipple. I calculated the effective area and found the maximum allowable stress for the material (316L) using the fatigue limit as by criteria. This is so it doesn't explode after 1000s of cycles!

The Barrel

I got the barrel a while back from I think onlinemetals.com I've had it in my storage room for a long time. It was actually the barrel sitting there and staring at me that inspired me to build this cannon because I wanted to shoot golf balls real bad! Its length is cut down to 24". The barrel is seated inside a very thin wall stainless 2" nipple with 2" - 1.5" abs adapter and bushing on the business end. On the end toward the valve I epoxied on a conduit bushing that can house an o-ring to seal the golf ball. This bushing had to machined down a great deal using my hand drill, vice, and hack saw so it could fit around the barrel and inside the 2” SS nipple. The thing on the muzzle is a 1.5" conduit slip coupling that I used to make a hop-up for the golf balls. It's just something I came up with on the fly. We'll see if it works!

The Valve

The valve housing is a SS 2" wye strainer. This is a "barrel" sealing piston valve where the piston seats against a big washer I soldered into the shoulder of the strainer basket seat. This washer provides a larger sealing and load bearing surface for the piston. Its ID is 1.375" (minimum area of valve). The cylinder which the piston slides through is a 2.25" OD steel exhaust pipe I soldered into the strainer housing. Both the soldered joint of the seating washer and the cylinder leaked (as expected, soldering steel to SS is extremely difficult especially in a tight internal space), so I used epoxy to seal it up!

The Piston

My 3rd attempt at a piston ended up working well! It is made from ABS pipe! I think my other two attempts are shown below. The diameter is 2.15". I heated the pipe with a heat gun, flattened it, drilled a buncha disks out with a hole saw, stacked them and glued them, and machined it to size. I chose ABS because it is more impact resistant than PVC and much lighter (coextruded foam pipe for DWV). The flat washer on the front seals off the valve and chamber while the two o-rings help guide and seal the piston during piloting. The o-rings is my secret to getting this large valve to open using only a blowgun. I made sure that everything was just right! Had to break out the digital calipers. I drilled a 1/16" hole through the piston to bypass the o-rings to allow the chamber to fill, but be small enough to not effect piloting terribly.

The Bumper

I made the bumper from cutting out circles of bike inner and gluing them together with contact cement. Very cheap since the inner tube was free! If you haven't noticed, inner tube was the star of the show here as I used it in multiple components. Try to find them all!

The Fill/Pilot

So I played Tetris with my available fittings and finally came up with a compact configuration that worked. The fill valve is a Shraeder and luckily enough, disconnecting a bike pump from the valve isn't enough to pilot the piston (yay!) so I didn't need to add a ball valve to isolate the fill. The pilot valve is just a plain old shop blowgun. It has enough flow rate to pilot the valve with little delay.

The Stock

I wanted to flaunt the piping as much as possible so I didn't make a big showy stock to detract from the cannon itself. I made it small and just enough to get the job done. It's also kinda goofy looking too! It's made from heating, bending, and cutting 1" PVC pipe. I painted it with some blue plastic rustoleum spray I had handy to protect it. And I wrapped the butt and grip with bicycle inner tube to get a nice grippy feel. The stock is secured to the chamber using inner tube as well wrapped tightly around many times. You'd think that this design would be kinda flimsy, but it is surprisingly rigid.

The Scope

Just an old airsoft scope. The exciting part is that the wye fitting had a nice rib running along the top that was a suitable width for a dovetail mount. I used a dremel to grind an undercut into the rib so that the scope mounts could get a bite. It ended up being very sturdy and straight!

Performance

I have not tested the cannon with projectiles yet! I am going to visit some friends this weekend so I hope to do it then. I wanted to get this info up here first and come back later to it. So stay tuned!

If you have any questions about my design (or improvisation) please ask!

And now the pictures:

What was the approximate build time on this? What kind of flux did you use for the soldering? Try and get some video for us to watch. It's a great looking cannon!

Grrreat questions! Thanks!

It took me 8 days to build this. I had lots of time because it was winter break from school. I used "Oatey No. 5 Lead Free Solder Paste" which is used for plumbing flux. I used silver bearing acid core solder "used for metal work" with it. In the future i'd recommend using MAPP for a hotter flame and a water soluble flux paste to make cleaning it out afterward easier.

One of my friends I'm seeing this weekend was a film major so he's got some quality equipment!

I made a diagram so you can all better see how I magicked the wye strainer into a piston valve:

magicked

Ok, I'm calling it, 1st new spudding term of 2016! :bigsmurf:

All you got to do is wish as hard as you can and magic will do the rest!
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Here's the experimental ammo I'm going to try in addition to spuds and gold balls. 1" couplings are a perfect fit for the barrel so I decided to take advantage of that. The one on the right is kinda similar to the Sureshot UHMWPE rounds that they make. We'll see what happens!

Those are gonna hit with a serious thud. Fill one of the heads with playdough or clay. Just thinking out loud...

Excellent work!

The stock is especially interesting. Great job on the valve internals as well, do you have any performance information as far as the valve opening times go?

Also, did you get any inspiration from clide's build here (pictures) or here (description)?

Good job again!

Thanks for the feedback! I don't have any data on the valve opening time no...

THERE IT IS!!!!

I was looking for that cannon for so long! I remember seeing that thing so long ago, and that's what inspired me to use a wye-strainer actually. I tried looking for that post, but couldn't find it. I loved (in my memory at least) how it was all inline and naturally suited to being held like a rifle or bazooka.

Extremely nice build, love the neatness of the configuration!

I'm not sure that "hop-up" is going to survive the first shot though - but in any case, do you actually need it? It's necessary for airsoft because a low density projectile fired at a relatively low velocity is going to tend to drop, a typical golf ball on the other hand is 4 times denser than a 0.25 gram airsoft BB, over normal ranges you're going to have a decent trajectory without the need for the magnus effect.

Update!

So my plans to see my friends didn't pan out so I wasn't able to fire the cannon over the weekend


Thanks! Yeah, I wanted to try this first hop-up design because it was very easy to make and doesn't require modifying the barrel itself. We'll see if it gets blown apart or not! From seeing other videos of golf ball cannons I notice that the balls hook pretty badly. I want to avoid that with this gun. But once again when I get a chance to shoot it, all will be revealed. While I wait for a chance to shoot I am making some big modifications so the next time you see it, the cannon will be a bit different looking! I'm just waiting for the wood glue and sawdust to finish drying. (four days and counting).

That's quite an interesting way to make a handle. Have you seen any of the posts by members like Hotwired and Ragnarok using "polymorph" for the handles? I can also say I've used modeling clay and an oven for a handle before, but can't attest to its durability since I didn't wind up using it...

I remember most the handle on Copperhead Prime made out of polymorph. The trouble is the low melting temperature. I wanted something that was more wood-like too. Hopefully it doesn't look like a turd when it's sanded. When mixing the sawdust into the wood glue it looked a lot like chicken salad. It looked quite tasty. Then it started to turned darker when it dried. And was about the same difficulty to work with as chicken salad. Next time I'd add a binder of some sort like flour or corn starch.

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UPDATE!

So I made a few improvements...

1) I modified the piston to have a thicker barrel seal using a thick 2" rubber cork. I did this because the piston bounces back after each shot at high pressures. The thinner seal was getting sucked through the washer sealing face causing the next shot to be impossible without resetting the piston.

2) The piloting layout is more in-line with the fill valve downstream of the blowgun. After removing the blowgun spring, the blowgun now acts like a check valve. To fire, the ball valve is opened to create an air path, then the blowgun trigger is pressed. The ball valve acts like a safety too. If the trigger is pulled with the ball valve closed, it won't fire.

3) I made a composite grip and butt stock using wood glue and sawdust.

4) The barrel is housed in a SCH80 PVC nipple. The barrel is choked down to a tighter diameter using a 1.5" length of SCH20 aluminum pipe epoxied into the PVC nipple. This holds/seals the golf ball tightly for each shot and ensures that the piston fully opens.

5) I shined up that beautiful SS!


Be sure to turn up the volume for the video! That way you can hear to cool echoes and impacts.

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