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pvc shells

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unread postAuthor: potatoflinger » Sat Mar 08, 2008 9:20 pm

This is actually really easy to do with a shop vac and thin plastic sheets (I use sheets of plastic from milk jugs, which are thin sheets of HDPE plastic). It is useful if what you are making is fairly small. What I usually use it for is making my own paintballs, what I do is form the plastic around a cylinder that is just a little smaller than the barrel that they are for (usually 1.5") and then I fill the vacuum-formed plastic cylinder with water and food dye. Then I take another sheet of plastic and melt it to the open side of the cylinder to close off the end. They actually make pretty good large caliber paintballs.

The method is very useful, but it is not worth the trouble unless you want to make something hollow.
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Unread postAuthor: base45 » Sat Mar 08, 2008 9:23 pm

well its nice to hear that it accually works. because i wasnt really sure
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Unread postAuthor: potatoflinger » Sat Mar 08, 2008 9:29 pm

It works, but you need to have something to vacuum form on. Here is a great instructable on how to do it: instructable
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Unread postAuthor: Pilgrimman » Sun Mar 09, 2008 1:05 am

I could see this being applicable to PVC, but only in low wall thicknesses, such as SDR-21. I remember that episode of Mythbusters, and I remember thinking how cool it was! I never thought to apply it to spudding, however! Nice thought!
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Unread postAuthor: base45 » Sun Mar 09, 2008 1:24 am

actually i tried this earlier today with milk jugs plastic and found that when you turn on the vacuum it spreads the plastic out so it becomes very thin so my suggestion would be to use thick material because it will end up being about 1/4 as thick when your done. :lol:
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Unread postAuthor: jimmy101 » Sun Mar 09, 2008 2:59 pm

Hotwired wrote:Bear in mind that a vacuum only creates (at an unlikely best) a 15psi difference across the sheet so material would need to be pretty soft or thin.


Ya, 15PSI max, BUT, take that 15PSI and spread it out over a 12" square and you have more than one ton of force. Even at just a half-atmosphere of vacuum there is still more than 1000 pounds of force on a 12" square.

It generally only takes a modest vacuum to vacuum form. A shop vac is more than adequate. The plastic sheet is heated to it's softening temperature and it takes very little force to form it.

When I was a kid you could buy a toy called a "Vacu-form" (think that was what they were called). The vacuum was generated with a very crappy hand pump and the system leaked like crazy but it still worked. It had a built in heater, a ~3"x3" hinged frame to hold the plastic sheet, the porous support that the mold was placed on etc. I suppose you can't get them anymore because they actually heated up hot enough to burn skin. Heaven forbid that any modern child's toy could actually cause injury.

Not sure how practical vacuum forming would be for making shells. Vacuum forming works very well for making many copies of moderately complex shapes (like a scale car body). For simple shapes, the form itself is easy enough to make that you might as well use it as the ammo. Plus, the plastic used in vacuum forming is pretty thin and probably won't stand up to the thousand or so G's of a spud gun.

EDIT: Here is a link to Mattel's Vac-U-form.

Looking at the original post again, I was too dense to pick up on the idea that the sheet is being sucked down into a piece of barrel. Might work. Need to get the PVC pretty hot though, and like others have posted, it is going to thin out a lot if the shell is more than an inch long. One problem though, you may need holes to pull the vacuum through all around the form, not just the big one at the end.
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Unread postAuthor: VH_man » Sun Mar 09, 2008 6:15 pm

Heaven forbid that any modern child's toy could actually cause injury.


stomp rockets arent dangerous like that? lol.

back on topic, i tried this out today, and it works amazing..........
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Unread postAuthor: base45 » Sun Mar 09, 2008 6:30 pm

VH_man wrote:i tried this out today, and it works amazing..........


oh really how did you do it?
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Unread postAuthor: VH_man » Sun Mar 09, 2008 7:34 pm

i used the "peanut butter jar" method. i just moulded some .62 cal cones........ they work better than the little wire nuts i moulden them from because they weight less. Ill post pics later.
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Unread postAuthor: base45 » Sun Mar 09, 2008 8:32 pm

VH_man wrote:i used the "peanut butter jar" method. i just moulded some .62 cal cones........ they work better than the little wire nuts i moulden them from because they weight less. Ill post pics later.


alright cant wait to see the pics
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Unread postAuthor: base45 » Mon Mar 10, 2008 4:35 pm

has anyone else tried this and had success? if so please take a pic of the shell/process to make it more clear what you did exactly
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Unread postAuthor: STHORNE » Mon Mar 10, 2008 4:40 pm

base45 wrote:has anyone else tried this and had success? if so please take a pic of the shell/process to make it more clear what you did exactly


I have done it before with a copper pipe (same diameter as barrel), some soft/half melted plastic sheets, and a wooden dowel.

instead of a vacuum, i used the dowel to push the plastic down the pipe, thus taking the pipes shape.

worked perfectly and in my opinion, is more fail-proof than using a vacuum. Only thing is, i had to custom make the dowel on a lathe so it had 2cm of clearance all the way around for the plastic, otherwise it would not be air tight.
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Unread postAuthor: base45 » Mon Mar 10, 2008 4:44 pm

thank you for posting that seems like a great idea i would have never thought to use a dowel. i will have to try that

by the way what kinda of plastic did you use
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Unread postAuthor: STHORNE » Mon Mar 10, 2008 4:52 pm

same as you....milk jugs.

i also used plastic bottles once, but i suggest you stick with the milk jug plastic. put it in the oven for 30 seconds at 350 degrees. makes it soft and pliable, yet not to the point where its too hot or molten.
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Unread postAuthor: base45 » Thu Mar 13, 2008 1:21 am

oh thats kool i use a heat gun and secure it to a frame then do the vacuum business i have to use 2 layers of milk jug tho do u?
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