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| jackssmirkingrevenge |
 Posted: 06/22/2007 4:43 AM Post subject: making epoxy pistons |
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space monkey
Joined: 15 Mar 2007
Posts: 6523
9946.55 Spud Bux
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Here's how I cast pistons out of epoxy:
As per the other casting tutorial, the first thing you have to do is get yourself some marine epoxy resin, like for example this stuff, the important thing is that it has low viscosity so it will flow well for casting purposes, and that it sets as a solid resin.
1) cut out a rubber disc slightly smaller (around 0.5mm or 0.02 inches) diameter as the tube in which your piston will travel. Drill/punch out (using a sharpened tube) a hole in the middle through which you can insert a bolt with a washer. If necessary, apply JB weld or araldite to ensure that the seal between the bolt and washer are airtight.
2) lubricate the sides of the tube in which you're going to cast with a very thin layer, anything from automotive grease to KY jelly will do as long as its not a substance that will disolve in the epoxy. Insert the rubber disc and make sure its face is at 90 degrees to the tube. It's important that the space between the disc and the tube is sealed, if the fit is tight enough you can smear grease to keep it sealed, if not a thin application of JB weld to fill the gap will do.
IT'S IMPORTANT THAT YOU HAVE EVERYTHING ALIGNED AND SEALED BEFORE YOU EVEN THINK ABOUT MIXING THE EPOXY - it will be too late to make adjustments afterwards, this method of construction is VERY unforgiving.
3) Once you're satisfied the seal is airtight, mix the marine epoxy and pour it. The length of the whole piston should be at least as much as its diameter. Note that epoxy is very heat sensitive, store it at room temperature before mixing - if not, use a baine marie to heat it up before mixing - (some valid pointers on cold temperature bonding). I find that syringes are ideal to mix it in the correct ratio, and always calculate roughly how much you need so you don't mix too much and have to throw it away - if you take care of it, a pack will last you through many different projects. Clean up any spills immediately or you'll regret it, this stuff sets hard!
Allow 24 hours (or more in cold weather) for complete curing, then tap out the piston with a wooden dowel or similar. Lightly sand the sides of the piston until it's a loose enough fit in your chamber tube to allow you to push it easily with one finger. Do this little by little as its very easy to remove too much material. The piston should now be ready for use.
To make a lighter weight hollow piston, follow the second diagram - cut a cylinder of foam approximately half the diameter of the piston and attach it to the bolt before pouring the epoxy.
Any queries, feel free to ask 
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| lightweight piston variation |
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Last edited by jackssmirkingrevenge on 03/07/2008 2:31 AM; edited 2 times in total |
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| spud yeti |
| Posted: 06/22/2007 5:05 AM Post subject: |
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can i change this name
Joined: 08 May 2007
Posts: 1043
14.05 Spud Bux
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Thanks for making this, it helps me understand it. How is the best way to pour resin in so that you dont get bubles of air in it. That happened to me once, and its frustrating!
Im making a gun using this and couldnt get it airtight, but with this help I will redesign my piston.
Woohoo! First post! 
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| jackssmirkingrevenge |
| Posted: 06/22/2007 5:20 AM Post subject: |
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space monkey
Joined: 15 Mar 2007
Posts: 6523
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| spud yeti wrote: | | How is the best way to pour resin in so that you dont get bubbles of air in it. |
To avoid bubbles, all you have to do is mix it and pur it slowly - however it isn't really important in this case, because the epoxy is low viscosity and therefore the bubbles will rise to the surfact, which is the back end of the piston.
It's really just an aesthetic thing, the only time I cared about bubbles was when I cast a jewel box as a present for my g/f (see attachment)
I mix my epoxy by clamping a piece of wood or plastic in an electric drill and blending away, it's bubbles galore but it never bothered me.
| Description: |
| LOTR themed jewel box cast in epoxy resin |
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| spud yeti |
| Posted: 06/22/2007 5:27 AM Post subject: |
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can i change this name
Joined: 08 May 2007
Posts: 1043
14.05 Spud Bux
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O ok cool. WOW thats such a cool box, see must have been happy (the returns great too!!  )
I mix PVA paint the same way as you, lol, its brilliant! Im trying to adapt an electric cooking beater for that use too!
I guess what youre saying about the bubbles is true, never thought of it like that!
btw, what language is that on the box??
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| jackssmirkingrevenge |
| Posted: 06/22/2007 5:30 AM Post subject: |
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space monkey
Joined: 15 Mar 2007
Posts: 6523
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It's her Elven name, she's a big lord of the rings fan 
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| spud yeti |
| Posted: 06/22/2007 5:36 AM Post subject: |
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can i change this name
Joined: 08 May 2007
Posts: 1043
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Thats hectic! I have a friend whose also into that a lot!
What is the name (like how would you say it)?
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| jackssmirkingrevenge |
| Posted: 06/22/2007 5:49 AM Post subject: |
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space monkey
Joined: 15 Mar 2007
Posts: 6523
9946.55 Spud Bux
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| spud yeti wrote: | | What is the name (like how would you say it)? |
Alassė. Poetic, isn't it?
*sigh*
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| spud yeti |
| Posted: 06/22/2007 5:55 AM Post subject: |
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can i change this name
Joined: 08 May 2007
Posts: 1043
14.05 Spud Bux
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mmm, very...
But back to topic, I only have one other question, and I think its because Im being stupid, but anyways... What are the grey pieces on top and below the green/black?  Whilst Im on embarrassing topics, and off topic, how do you get a picture near your name, because everyone has them and Im curious!
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| jackssmirkingrevenge |
| Posted: 06/22/2007 8:31 AM Post subject: |
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space monkey
Joined: 15 Mar 2007
Posts: 6523
9946.55 Spud Bux
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| spud yeti wrote: | | I think its because Im being stupid, but anyways... What are the grey pieces on top and below the green/black? |
Yeah, you are   that's simply the rest of the pipe...
| spud yeti wrote: | | how do you get a picture near your name, because everyone has them and Im curious! |
Simple, click on "profile" on the toolbar at the top of this page, scroll down to the "avatar control panel" and upload an image.
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| markfh11q |
| Posted: 06/22/2007 8:53 AM Post subject: |
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Magic Dust Man
Joined: 06 May 2006
Posts: 1387
273.60 Spud Bux
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| Nice tutorial. I liked some of your designs, though, that included a syringe tube piston housing and the piston as the syringe plunger. Any specifics on what type of tubing a syringe tube will fit into?
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| jackssmirkingrevenge |
| Posted: 06/22/2007 9:59 AM Post subject: |
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space monkey
Joined: 15 Mar 2007
Posts: 6523
9946.55 Spud Bux
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| markfh11q wrote: | | Nice tutorial. I liked some of your designs, though, that included a syringe tube piston housing and the piston as the syringe plunger. Any specifics on what type of tubing a syringe tube will fit into? |
That's even simpler to make, simply remove the plastic plunger and just put the rubber seal in the syringe tube, make sure it's straight and just pour the epoxy in the back as per the diagram.
However I must point out that I stopped using this sort or piston for two reasons:
1) Due to the perfect seal, you either need to put a filling valve in both the chamber and the pilot area, or make a connection from the pilot area to the chamber with a check valve in the middle.
2) The tight fitting rubber creates a lot of friction which doesn't allow the piston to move fast enough for optimum performance.
Personally, I would recommend the revised design that is the subject of this tutorial.
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| Velocity |
| Posted: 06/22/2007 12:48 PM Post subject: |
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Brigadier General
Joined: 07 Feb 2006
Posts: 949
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Could you possibly provide a picture of one of your finished pistons? Though, I wouldn't be suprised if you did not have one on hand, because all of your guns are epoxied together, right?
Nice tutorial. I have tried to make an epoxy piston before. I used cooking spray to lubricate a piece of 1" SCH 40, and after the epoxy set, it wouldn't come out. It took plenty of banging and smashing to finally knock it out. When it did come out, it was not a very round shape; many surface bumps and stuff. I ended up throwing it away and using a length of 1" UHMW rod as a piston instead.
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| jackssmirkingrevenge |
| Posted: 06/22/2007 14:50 PM Post subject: |
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space monkey
Joined: 15 Mar 2007
Posts: 6523
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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" ) 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.
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| sandman |
| Posted: 06/22/2007 16:06 PM Post subject: |
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Colonel
Joined: 15 Mar 2007
Posts: 648
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| im just wondering if there is a reason for the color variations in the piston
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| Velocity |
| Posted: 06/22/2007 16:29 PM Post subject: |
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Brigadier General
Joined: 07 Feb 2006
Posts: 949
25.42 Spud Bux
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| Damn thats clean... smooth and round. Thanks for the pictures.
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