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Rabid's Coaxial Tennis Ball Cannon

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: Heimo » Sun Jan 03, 2010 6:58 am

RabidDuck wrote:Centered barrel and tried filling but still no luck. May pour small layer in bottom of piston since i don't know what else it could be. Do you think i should try getting a new type of rubber like neoprene?


you can also try to form a sealing face from silicone rubber take the old stuff off then get a pane of glass put some petroleum jelly on it to prevent the silicone from sticking then get some silicone gasket sealer (any hardware store should have it) then smear the silicone on the piston then lastly place the piston on the glass so your sealing face is nice and flat after the silicone cured trim it and then let me know if it worked :D
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Unread postAuthor: jrrdw » Sun Jan 03, 2010 7:18 am

Heimo wrote:you can also try to form a sealing face from silicone rubber take the old stuff off then get a pane of glass put some petroleum jelly on it to prevent the silicone from sticking then get some silicone gasket sealer (any hardware store should have it) then smear the silicone on the piston then lastly place the piston on the glass so your sealing face is nice and flat after the silicone cured trim it and then let me know if it worked


That wont work for 2 reasons, 1) the sealing face is down inside the cup. 2) Silicone is to soft. Picture's of the piston are on the 1st post, page 1.
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Unread postAuthor: Heimo » Sun Jan 03, 2010 8:27 am

@jrrdw

Ok please explain why silicone is too soft cause I do not know

also if silicone is unsuitable how about Urethane Rubber
you can buy some here a little expensive to my taste (30$ for the trial size) but this is a pourable product so you can pour it inside the piston and it will self level so it will be nice and flat

http://www.smooth-on.com/PMC%3D--870-Uretha/c1147/index.html

this is what they said about it
It is also suitable for rubber mechanical parts of varying configurations (gaskets, wheels, pulleys) as well as ball mill liners and vibration/shock pads.

seems like pretty tough stuff to me
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Unread postAuthor: jrrdw » Sun Jan 03, 2010 9:16 am

Silicone rubber will tear under these conditions due to constant pushing and pulling, (sealing & unsealing/filling & firing).

Urethane rubber is different, what you linked to just might work. It has a 70% hardness witch sounds to me like it's comparable to neoprene rubber. The only problem that I can see up front is the cost, works out to be approx. $10.XX a pound, minimum order 3lbs.

That's a good website you found Heimo.
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Unread postAuthor: jackssmirkingrevenge » Sun Jan 03, 2010 9:17 am

jrrdw wrote:Silicone rubber will tear under these conditions due to constant pushing and pulling


I'm trying really, REALLY hard not to comment :D
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Unread postAuthor: spudtyrrant » Sun Jan 03, 2010 9:27 am

or he could just get some good ole' neoprene from mcmaster and put it in after leveling the face out with the fiberglass, I recommend 3/16", a 12" by 12" sheet will last you quite a while
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Unread postAuthor: jrrdw » Sun Jan 03, 2010 9:51 am

jackssmirkingrevenge wrote:
jrrdw wrote:Silicone rubber will tear under these conditions due to constant pushing and pulling


I'm trying really, REALLY hard not to comment :D


Oh? "really, REALLY"

Keep in mind it's all theory until you do it. It's been my experiences using "silicone" rubber in any kind of "moving" application it works loose, tears, separates from what I applied it to etc...
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Unread postAuthor: RabidDuck » Sun Jan 03, 2010 9:58 am

Is there next day shipping that mcmaster can do? Because the school project is due Thursday i think and if i order it and don't get it until Wednesday that may not be enough time. If so i will end up using my golf ball cannon and work on this one throughout the next week. Do you think its the sealing face that's the problem? The lipstick test proves that everything is flat and it makes a full ring; yet it still leaks out the barrel.
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Unread postAuthor: jrrdw » Sun Jan 03, 2010 10:15 am

RabidDuck wrote:Is there next day shipping that mcmaster can do? Because the school project is due Thursday i think and if i order it and don't get it until Wednesday that may not be enough time. If so i will end up using my golf ball cannon and work on this one throughout the next week. Do you think its the sealing face that's the problem? The lipstick test proves that everything is flat and it makes a full ring; yet it still leaks out the barrel.


It very well could be.

As for next day shipping goes you have to figure in the time it takes to create invoice, pick the part, package it and wait for the pick up from deliverly service and that normally can take up to 2 days, then your next day shipping takes place.

I don't think you will get it in time, but would still be a good idea to get it for your sealing uses. Don't waste any money on next day shipping, go standerd and save yourself 12 or so dollars.
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Unread postAuthor: RabidDuck » Sun Jan 03, 2010 11:02 am

Ok so what should i get from mcmaster? Neoprene or Urethane rubber and how much would that cost? A certain width that would work better than another?
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Unread postAuthor: jrrdw » Sun Jan 03, 2010 2:52 pm

Get Neoprene, and I think it comes in 1 foot by 1 foot squares, 1/8th inch thick should do nicely.
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Unread postAuthor: clemsonguy1125 » Wed Jan 13, 2010 4:57 pm

Try putting petrorleum jelly on the piston I had the same problem but that fixed it.
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Unread postAuthor: RabidDuck » Thu Jan 14, 2010 7:41 am

Sorry for being away for so long. I'm near the end of my first High School semester so i have been busy with that. The piston is fiber glass but i will try putting some on. I haven't been able to get on mcmaster and look for any rubber yet either. Plan on looking for some later tonight after school.
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Unread postAuthor: inonickname » Thu Jan 14, 2010 8:03 am

jrrdw wrote:
jackssmirkingrevenge wrote:
jrrdw wrote:Silicone rubber will tear under these conditions due to constant pushing and pulling


I'm trying really, REALLY hard not to comment :D


Oh? "really, REALLY"

Keep in mind it's all theory until you do it. It's been my experiences using "silicone" rubber in any kind of "moving" application it works loose, tears, separates from what I applied it to etc...


Ahh..I now understand why you said this:

I've been kicked out of every girls house i've walked into! Once i got kick out 3 times, (had to dodge the cops the 3rd time, dorks). Everybody with a daughter in my home town hates me still to this day. Must be all the sneaking around.


May be time to throw more funds into crash helmets :) (by lord, we don't need more JRRDW's wandering around).
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Unread postAuthor: jrrdw » Thu Jan 14, 2010 12:46 pm

inonickname wrote:May be time to throw more funds into crash helmets (by lord, we don't need more JRRDW's wandering around).


That may or may not be a problem, there was this rumor going around but nobody sent out any summons or anything alike.... :wink:
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