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making epoxy pistons

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Unread postAuthor: niglch » Sun Mar 02, 2008 8:30 pm

JSR, can you please repost the links to the kind of epoxy you used (they seem broken)? The only kind of marine epoxy I could find at Home Depot was the kind that comes in 25mL syringe bottles and it is really, really thick stuff (definitely not low viscosity like what you were talking about). It was tough as anything to mix and it didn't bond very well to the rubber (although this may have been a result of the difficulty I had mixing the stuff). However, it did a very good job bonding to the sides of the PVC mold even though I had covered them with cooking spray.
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Unread postAuthor: bigbob12345 » Sun Mar 02, 2008 9:35 pm

niglch the low viscosity epoxy he used is called marine epoxy they should have it at your local home depot if they dont ace and lowes have them to.
and about it sticking to the wall things white lithium grease and other similar greases are better cooking oil just doesnt cut it with epoxy.
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Unread postAuthor: niglch » Sun Mar 02, 2008 11:47 pm

Thanks,
Here is a picture of the epoxy I used:
Image.
It does say that it is marine epoxy (the picture is kind of small so it's a tad hard to read), but it was some really thick stuff. I guess I should look for a different brand.
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 03, 2008 12:02 am

It's important that it's low viscosity, otherwise it's hard to cast, what you want is something like this stuff.
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Unread postAuthor: Jared Haehnel » Tue Mar 04, 2008 9:26 am

Thanks Jack this has been very informative....

Would you recommend this for larger pistons...say 4" in diameter... and whats the cost of the epoxy?
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Unread postAuthor: bigbob12345 » Tue Mar 04, 2008 9:44 am

This is not something for larger pistons.
A 4in piston is going to cost you $40-50 of epoxy and wouldnt be worth it.
For 4in pistons most people use a 3in endcap sanded down.
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 04, 2008 10:01 am

The technique does lend itself more to smaller pistons, however with a bit of ingeniuty and common sense it can be adapted on a larger scale without a corresponding increase in cost and weight. I would go with something like the design illustrated below (assuming it's for a coaxial design) that gives you a piston long enough for stability but which makes minimum use of epoxy making it relatively cheap and light, and also gives you a flat piston base meaning no unnecessary pilot volume is added.

Jared Haehnel wrote:... and whats the cost of the epoxy?


Going by this advert, a mere 20 bucks will get you 32oz of the stuff, not exactly prohibitive costs.
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Unread postAuthor: Jared Haehnel » Tue Mar 04, 2008 10:12 am

Thanks that helps out a lot. I just realized how I can make the valve a heck of a lot simpler to build... 8)

it's important that it's low viscosity


I'm guessing Bondo is out then....darn
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 04, 2008 10:24 am

Jared Haehnel wrote:I'm guessing Bondo is out then....darn


Definitely, you can't cast with a putty :p but the one I linked to is more than suitable and for less than 20 dollars won't break the bank.
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Unread postAuthor: Counterstriker » Sun Mar 09, 2008 7:25 pm

Excuse my ignorance I am a noob :D But when you say set in tube do you mean the air tank your gonna use? Sorry I am an idiot!
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 10, 2008 3:34 am

The piston travels in a tube, it could be a Tee fitting or it could be the outer pipe of a coaxial chamber, the important thing is that you cast the piston in the same pipe it's going to be fitted in to get as close a fit as possible.
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Unread postAuthor: Counterstriker » Mon Mar 10, 2008 3:26 pm

jackssmirkingrevenge wrote:The piston travels in a tube, it could be a Tee fitting or it could be the outer pipe of a coaxial chamber, the important thing is that you cast the piston in the same pipe it's going to be fitted in to get as close a fit as possible.


Thanks :D But I didn't see an O'ring on the picture of you piston, are the nessecary?
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Unread postAuthor: STHORNE » Mon Mar 10, 2008 4:35 pm

it would be best if you used an o-ring, because most likely, the piston you make will not be perfectly air tight. you could just make your own o-ring by cutting a section of a piece of rubber tubbing that tightly fits the T fitting.
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Unread postAuthor: Counterstriker » Mon Mar 10, 2008 5:41 pm

sthorne wrote:it would be best if you used an o-ring, because most likely, the piston you make will not be perfectly air tight. you could just make your own o-ring by cutting a section of a piece of rubber tubbing that tightly fits the T fitting.


I alot of paintball co2 tank o-rings and hose o-rings. Should I just carve a notch in the piston to hold the o-ring? I thought it shouldn't be to airtight to allow ai to fill the chamber.
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Unread postAuthor: STHORNE » Mon Mar 10, 2008 5:43 pm

well, your kinda missing the concept.

are you making a coax or a regular T piston gun?
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