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hot glue piston q's

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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hot glue piston q's

Unread postAuthor: homedepotpro » Mon Apr 09, 2007 9:03 pm

i have a few questions. i m building a coaxal and i need to know a few things about the piston
1. i have a idea for an equalization tube in my piston, it is covered in the front by the edge of the sealing face which i m hoping will act as a sort of check valve. do i need this or is there a better way of doing it?

2. the barrel is 1/2'' so i figure it would be better to put 4 screws towards the outer edge of the sealing face as to not interfere with the seal with the barrel p.s.(2'' chamber). would it be better to just put one screw and washer in the middle?

3. is it better to have a spring behind the piston?
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Unread postAuthor: mopherman » Mon Apr 09, 2007 9:07 pm

1 just drill a small diameter hole for equalisation (sp?)
2 dunno
3 if you dont have a spring you should probably have a bumper
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Unread postAuthor: homedepotpro » Mon Apr 09, 2007 9:09 pm

well im going to have a bumper for sure
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Unread postAuthor: keep_it_real » Mon Apr 09, 2007 9:12 pm

1. I like the equalization idea. Thats nice.

2. It depends on the psi of the rubber. If it can hold enough, you don't really need a screw there. I would just put one there anyway along with the screws around the barrel.

3. what mopherman said
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Unread postAuthor: homedepotpro » Mon Apr 09, 2007 9:50 pm

what is the best lube for the piston or do i even need any
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Unread postAuthor: frankrede » Mon Apr 09, 2007 10:17 pm

Lithium grease
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Unread postAuthor: singularity » Mon Apr 09, 2007 10:28 pm

lube will only make the piston work better, its not required. lithium grease or any other non petroleum based lube will work.

ps - if its going to be made from hot glue why not add some o-ring groves, it will improve performance
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Unread postAuthor: homedepotpro » Mon Apr 09, 2007 10:32 pm

how do they improve prefomance, im goint to make the piston the same size as the id of the pipe, won't grouves just reduces the amount of surfaces area with the pipe wall
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 10, 2007 2:32 am

are you sure an equalisation hole is needed?
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Unread postAuthor: Insomniac » Tue Apr 10, 2007 2:49 am

@homedepotpro:
The point of O-ring grooves are so you can put O-rings in the groves (duh) and this will make the seal against the pipe better, and make the piston slide easier (so long as the grooves are cut very accurately)
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Unread postAuthor: paddo » Tue Apr 10, 2007 7:04 am

yes o rings do make them seal better. they are not neccesary but they most likely will increase performance. good luck with it mate it looks good so far. i like that im going to have to try it soon.
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Unread postAuthor: lukemc » Tue Apr 10, 2007 7:19 am

jackssmirkingrevenge wrote:are you sure an equalisation hole is needed?


if he dosent have a equilization hole wont it jut pressurize behind the piston?
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 10, 2007 7:41 am

lukemc wrote:if he dosent have a equilization hole wont it jut pressurize behind the piston?


Assuming the piston is 100% airtight, this will happen, but I doubt this is the case without o-rings
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Unread postAuthor: Matheusilla » Tue Apr 10, 2007 8:47 am

I've fastened rubber on the piston's sealing face with screws around the perimeter instead of the middle. The things to consider are:

1) The rubber has to be able to hold the pressure and not burst into the barrel, like "keep_it_real" said.

2) If the rubber is thin and flexible enough, it is somewhat difficult to keep it from bunching up in the middle.

P.S. Make sure the screws are either screwed into something solid or are really long because they can/will be pulled out when it fires.

P.P.S. Try to put washers on your screws so that the rubber won't be pulled off the screw heads.
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Unread postAuthor: mopherman » Tue Apr 10, 2007 2:28 pm

if you mix pvc dust in with the hot glue, do you think it would make it lighter?
or would it just weaken the piston? :violent3:
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