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Hey! First post here, what a great forum. So much info here that it's kept me busy for the last few weeks trying to take it all in!
But anyway, here's my first go at a cannon with a little build report. I hope the pics aren't too big but if they are just say and I'll resize them.
The design is your average old barrel sealing piston valve built into a t piece pvc cannon with some parts machined out of delrin. I just wanted something simple to get me started. I intend to eventually build a huge piston valve actuated pneumatic ram for one of my battlebots so making something like this is a good introduction i guess!
So onto the build. The construction was limited by what i could get at bunnings (from Aussieland btw), so nothing is particularly ideal. Keep that in mind
Chopping up the bits of pipe on the abrasive saw. It seemed to give the best surface finish of any tool i tried. Super quick too. The pipe is pn18 grade for the fittings, pn9 for the "tank" and pn12 for the barrel. Unfortunately that's the best you can get at most tool shops here, so 100psi max will have to do.
Lathing the ridge out of the reducer so the barrel can slide all the way through it.
Turns out the first one i got was manufactured wrong and wouldn't seat properly into the T piece. You can see it sitting a fair way proud of the surface in the below pic. So that gun assembly is pretty well junk, though it may get turned into a low pressure net gun later
The second one worked flawlessly though. Did i mention the pvc cement and primer is the messiest stuff known to man? well it is for me at least XD! anyone got any tips for stopping the glue going everywhere or is it just a fact of life?
I put the barrel a little less than half way in, in this one, i figured it would flow a bit better then having it half way.
The pipe is 36mm and 50mm respectively IIRC.
Next up is machining the rear bulkhead. I didn't want to use a glued PVC fitting because the piston was going to be fairly heavy at around 200 grams. Having it fire out the ass end wouldn't have been too pleasant lol.
This 80mm piece of delrin i was given should work nicely. Unfortunately though it was basically cut off at the finished length, so i couldn't really hold it in the chuck. Just pressing it against the chuck with the tailstock works great for plastic however.
All machined to size. To install it requires a firm push but nothing excessive. It still needs the o-ring and mounting holes drilled, but we will come back to that later
Next up is the important part. the piston. Made from a longer piece of delrin which was also cut to roughly the finished size. The same technique was used to make it. Here's the finished piece. Its about 55.5mm diameter and 57mm long with a weight of 214 grams.
Some details about the design of it -
There's a small stub on the end that locates the sealing washer, it protrudes about half way into it. The hole in the center is tapped for m6 to keep the end cap attached.
Now the funky part. I noticed a few topics about issues with the barrel sealing. So i tried something a little different. These washers have a ridge on the front of them. So i lathed a cap out of aluminium that, when bolted down, would press on the center of the washer forcing the edges to lift a little, which should help it seal against a not so perfectly flat pvc barrel (hey it happens )
Seems to work nicely
There's always a catch though, and it was the washers being too big in diameter by a fraction of a tenth of a bees d**k Damn! A jig was cooked up to hold the washers in the lathe while i dremeled them down in the lathe. I figured replacements would be needed so having the tool to just crank them out is always handy.
All seated nicely in the T piece. The barrel was lapped with sand paper glued to a conveniently sized piece of aluminium rod. I got glue all over it so that took some time As seen its a small ratio design.
Here's the internals layed out. Theres a 15mm foam chunk between the end cap and the piston which takes up half that space between the two pieces. So the pilot volume is pretty minimal.
Speaking of bumpers here it is being made. It's just a camping sleeping mat i had around. A friend used the same stuff in a 1000psi pneumatic ram as a bumper so this will do nicely. Turns out it lathes pretty good for foam too
In position with the finished end cap. You can't really see it but there's a 1/4" BSP threaded hole in the center of it. Why is white delrin so hard to photograph? Arhrahhghghgh?!
The valve work that will almost certainly be temporary. 1/4" T piece onto nitto style quick disconnect fittings. One goes to the compressor to charge and the other goes to a air duster gun to vent the pilot. (We'll come back to that disaster of an idea soon >.>)
Here she is all ready to go The end cap bolts on with 4x m6 stainless bolts that are done up only very lightly. Don't want to deform or crack the pvc after all.
Time to fire! I slowly cracked open the valve on the compressor, feeling the piston slide foward with a thud and the air equalised around the piston. Standing well away i fired the air gun annnnndddd....
Nothing happened. At all The air just slowly dribbled out the air gun and piston only slid back when there was maybe 5psi left in the thing. It seems way too much leakage around the piston and a completely crap pilot valve was to blame there. After multiple tries air was starting to leak out the barrel too.
Sooooooo it all came apart again.. Little PVC particles on the pistons sealing washer was stopping that sealing (i sanded the inside of the tube it slid in and forgot to clean it out.. whoops) But the leakage around the piston was fairly major even with tight tolerances. On a small ratio valve with a poor pilot it just wasn't going to work. An o ring and equalizer port (1.5mm diameter) was the only way to fix it.
It isn't a floating o ring because i didn't have the right size o ring. They are really hard to come by here. 31mm is way too small and 32mm is way too big. So i just stretched a 31mm one over the piston. Just got some urethane o ring material that you melt together to make your own o rings though so i'll try that later on.
To fix the poor pilot valve i basically just yanked the quick disconnect out of the compressor to dump the air out. Lo and behold - IT WORKED Here it is at 30psi firing a golf ball into some 7mm thick plywood. The air leak sound is the air pissing out the air gun that i had cracked open to help the pilot vent faster.
Annnnd that's where I'm up to now Tommorow i need to sort out a much better pilot valve and start winding up the pressure. Sprinkler valves are really expensive here and ball valves are pretty tiny. So i reckon a custom made mini 1/2" Quick dump valve will get the job done. Then i can remotely fire it with a servo if i want.
I'll definitely have some more questions later though regarding some ideas to improve it, like cutting out piston weight etc.
Lastly here's the GGDT data on it
Oh and the parts for a much more serious QDV cannon i hope will run off of full pressure CO2. (its all 6mm walled steel pipe) Which should be pretty awesome.
Cheers for checking out my long winded ramble anyway XD! More to come.
Last edited by Desmo on Thu May 31, 2012 3:19 am, edited 1 time in total.
Cheers And yep! Its getting a quick dump valve made tommorow for a pilot valve so that should completely solve that. I hope lol.
Traditional PVC cannon meets machine tools, what a fantastic combination!
Brilliant job, way to introduce yourself to the forum
On a more practical note, the equalistation hole can be replaced by a floating o-ring, certainly not a problem with your tooling, and yes, an efficient pilot valve is definitely in order.
Good work, and I like your tools. I do not think that reducer was manufactured wrong, thats just how they are. A piece of 2 inch schedule 80 does the same job as this piece if you ever make another one.
Very clean my friend,,, now lets get some video of that beast in action,,
Nd next paint her nd give her a name!!
To fix the very messy glue, use gravity. It dribbles downhill. Tip your parts from horizontal to nearly vertical, then apply glue.
With care primer and glue can be added on the pipe and not dribble down the pipe.
Nice build. You may wish to double or triple your bumper thickness.
PVC has a nasty habit of stress cracking and failure in the pilot area.
To reduce barrel leakage, temporarily add fine sandpaper on the face of your piston and polish your valve seat to a flat true surface.
Very good work, good seeing more Australians here.
I've seen clear primer at Bunnings, or perhaps Home hardware, that'll sort out the primer stains.
Also, just an FYI, don't listen to Gun Freak, hybrids are the best thing going.
Practice makes perfect!
Cheers everyone, the kind words mean alot
@mattyzip77 - good to know! I'm pretty sure the first reducer was stuffed because a grabbed a few others and they all went in easy + sat flush dry, this one wouldn't even go halfway in with glue and all.
@Technician1002 - Nice I'll definitely try that next time. Seems like another problem i had was caking on the glue big time. When i had them together there was a giant bead around the edge so i wiped it off which made the mess. Guess ill go a bit easier on it next time lol! What do you think of just applying the glue to one piece (but primer to both) to stop the glue smearing along the pipe when its inserted into a reducer say?
Interesting about the bumper size as well. Will probably play around with it once the pilot problem is sorted, cause I'm not sure if the piston really needs as much travel as it does. So trading some piston travel for decreased pilot volume could well give it a big performance boost.
@ Zeus - Sweet as! Its a bit hard making these things in suburbia though, thankfully ill be going to a giant property in the middle of nowhere next week so unlimited testing time and targets ftw XD. Should be able to lob some heavy projectiles at 100psi out there.
Wouldn't mind a hybrid either, They do look pretty sick. But my friend (who's a better machinist then me by far ) wants to make a design that uses two coaxial chambers. The outer with a piston valve and 1000psi CO2 to fire a metal ring down the 2nd coaxial chamber which causes pressure to spike to a huge level into the middle chamber that has a burst disk. So we may do that one first
@Gun Freak - Thanks Looks like I'll be getting tons of practice soon haha.
@jsefcik - Good idea, Anyone got any ideas for names or paint schemes? Was thinking of calling it fwomp on account of the noise it makes lol.
Here's some videos. First video is just a dry fire at 60psi to make sure the piston wont explode out. All good
This ones a 30psi (i said 60psi but it was 30 in the end) shot of a duct taped toilet roll. Not too bad. But yeah that pilot is definitely a problem! Need to get that sorted very soon.
More serious shots soon
yeah they do have it, the green colour ones are for high pressure but they are all made from the same stuff.
@Desmo were in aus are you mate? im in Melbourn
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Add me on ps3: wannafuk, 8/11/11 cant wait
Did you get rid of all that blue hose? It will pilot a hell of alot better if you do and be more powerful. Also dont be afraid of it when firing it. The pvc could crack from even a short fall.
Looks great! I love the piston especially! Strange, when i tried to machine rubber it just ripped and balled up I should really make a piston valve like that, I've got some 2" delrin stock lying around somewhere...
My cannons | My QEV cannon |
Matty- nah not yet. Got caught up with other stuff and didn't get the chance to make a QEV for the pilot. More pics and stuff to come when i get round to it.
sharpshooter11000 - Yep you can't really machine rubber and super soft things with lathe tools. Even with a high angle of keen-ness on the tool it'll still chunk up. A dremel mounted in the tool post with a sanding drum is the only way to get a decent finish it seems.
Might as well throw up some more random pics. Here's a compressor for a friend in the making. It's powered by a MASSSSSIIIIIVEEEE 3000w outrunner brushless motor driving a piston pump directly.
The cylinder and piston still has to be replaced with much stronger ones, then its ready for testing. No idea what pressure it will get to as he only wants it to charge the system to 150psi as quick as possible, but am cautiously optimistic it will make it to 500psi No doubt another one will be made to run the steel cannon.
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