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making epoxy pistons

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Unread postAuthor: mopherman » Sat Jul 14, 2007 8:34 pm

jackssmirkingrevenge wrote:Coincidentally I have a few photos to hand, this is a 1" piston that fits in a syringe tube which I recovered from one of my 3/4" coaxials which I dismantled (for which read "destroyed" :D ) recently. Note that to save some weight (though not that much really, it was mostly done for pointless cosmetic purposes) I used the end I chopped off a permanent marker casing to create the "hollow" section at the back. well, I thought it looked cool.

why did you destroy the gun?
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Unread postAuthor: jackssmirkingrevenge » Sun Jul 15, 2007 10:31 am

It was surplus to requirements to I stripped it for parts, I wrote "destroyed" because with epoxy, things are pretty permanent and you can't take it apart without breaking it.
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Unread postAuthor: mopherman » Sun Jul 15, 2007 12:05 pm

oh. how do you usualy atatch your small diameter sealing faces? a screw would not fit in a bb barrel.
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Unread postAuthor: jackssmirkingrevenge » Sun Jul 15, 2007 12:41 pm

mopherman wrote:oh. how do you usualy atatch your small diameter sealing faces? a screw would not fit in a bb barrel.


for smaller diameters (and i´ve done this with 3/4" cal launchers too, like theo ne in the showcase) I prefer to attach the sealing component to the barrel and simple have a solid piston, like in this design:

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Unread postAuthor: mopherman » Tue Jul 17, 2007 8:41 am

thats a good idea. i just realized how hard it must have been to get that barrel dead center using epoxie. or did you use supports?
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 17, 2007 9:44 am

I use a jig ;)

What I did in this case was wrap a 6mm rod (barrel caliber was 6mm) with masking tape until its the same diameter of the inside of the chamber - this is then stuck into the breech end of the barrel, with the tape inside the chamber. If you've cut the disc on the other end accurately, it will kepp the barrel dead centre.
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Unread postAuthor: jackssmirkingrevenge » Thu Jan 24, 2008 11:16 pm

here's another example of what can be made using this technique, resulting in a light, strong structure that is also economical with materials:

Image


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Unread postAuthor: niglch » Mon Feb 04, 2008 8:31 pm

How thick does the layer of neoprene need to be? I was able to find neoprene washers as Home Depot the perfect shape for a 2" piston. However, they were rather thin if you have ever seen them (approximately 1/16"). Will they still be sufficient as a sealing face or should I look for some thicker stuff (and where is the best place to find it)? Also, will cooking spray and petroleum jelly work as lubricants?
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Unread postAuthor: Sticky_Tape » Mon Feb 04, 2008 8:41 pm

I am making a piston valved canon and I am using vegetable oil.
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Unread postAuthor: Alabaster » Mon Feb 04, 2008 9:02 pm

Now i am not getting what you are using as a mold just a pvc pipe right?
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Unread postAuthor: niglch » Mon Feb 04, 2008 9:32 pm

Alabaster wrote:Now i am not getting what you are using as a mold just a pvc pipe right?


The mold needs to have the same inner diameter of whatever the piston needs to move through. Usually yes, this would just be a small section of PVC pipe or a coupling depending on how you want to design your piston (I have seen both used). As long as you use some kind of lubricant on the sides of your mold, the epoxy will not bond to it and can be easily tapped out.
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Unread postAuthor: jackssmirkingrevenge » Mon Feb 04, 2008 10:59 pm

niglch wrote:How thick does the layer of neoprene need to be? I was able to find neoprene washers as Home Depot the perfect shape for a 2" piston. However, they were rather thin if you have ever seen them (approximately 1/16"). Will they still be sufficient as a sealing face or should I look for some thicker stuff (and where is the best place to find it)? Also, will cooking spray and petroleum jelly work as lubricants?


The thicker the better but 1/16" should be enough. I prefer to use automotive grease as a lubricant, it tends to be stickier and more reliable and you really don't need a thick layer, just apply and wipe off with a tissue, it leaves a thin film that allows you to tap the piston out.
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Unread postAuthor: Hawkeye » Mon Feb 04, 2008 11:03 pm

Good thick neoprene can be found where fittings are sold for making exterior vents watertight. Home Depot sells it for sealing around bathroom pipes venting out of a roof.
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Unread postAuthor: Alabaster » Mon Feb 04, 2008 11:47 pm

Oh yea, what is that inpression in the back of your piston?
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Unread postAuthor: jackssmirkingrevenge » Mon Feb 04, 2008 11:53 pm

Alabaster wrote:what is that inpression in the back of your piston?


The centre of the piston is hollow to save on weight and epoxy, I made the cast by wrapping duct tape around a syringe plunge.
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