Posted: 06/22/2007 2:21 AM Post subject: epoxy casting how-to
space monkey
Joined: 15 Mar 2007 Posts: 7401 12019.84 Spud Bux
I decided to do a little write-up for those that might be interested in applying the construction methods I've developed using epoxy to their own projects.
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.
Now, on to the construction. The example in this case is an endcap with a schrader valve mounted inside it.
1) roughen the surfaces of the pipe where the epoxy is going to adhere. You can get by with rough sandpaper but I like to use a broken drill bit or file to make deeper grooves and promote better adhesion.
2) cut out a disc from foam sheet (I find that polystyrene meat trays are a good cheap source for this material) the same diameter as the inner diameter of the tube, cut a hole for the schrader valve and stick it in place with JB Weld, Araldite or similar. It's important that the joint is airtight as it has to stop the liquid epoxy seeping through.
3) fix the disc in the tube with the adhesive used in 2), again making sure that the seal is airtight all round.
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.
4) mix the marine epoxy resin and pour it in place, giving it at least 24 hours to cure completely. 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!
The thickness of epoxy you use depends on the calibre and intended pressure. For a 1.5 inch tube, 1/4" thickness of epoxy is enough to hold at least 100 psi. You can also reinforce the epoxy (think reinforced concrete) by laying discs of wire mesh or similar stronger materials before pouring in the mix.
Any queries, feel free to ask
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Last edited by jackssmirkingrevenge on 03/07/2008 1:32 AM; edited 4 times in total
Nice method... did you create such a method yourself for spudgunning applications? Sure, plenty of people have tried epoxy as a construction material... but few people have it down to such a science as you do .
One question: Why do you choose to work with epoxy in this manner instead of using standard pipe fittings and such?
I can't say I "created" this method but I've certainly developed it to suit my needs over the years. The problem with standard fittings as I see it is that they limit your creativity, and force you to build within certain dimensions - I enjoy the liberty of being able to cast my own parts as the situation demands, it usually allows me to create more compact and, more importantly for me, more efficient launchers.
Sure, it's at the expense of being able to dismantle and service one's creations, and is also a much longer build time waiting for bits to cure, but considering the benefits it offers I consider it a small price to pay.
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lol
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