Epoxy Moulding

[Nigel Bennett]

OK, so I want a wheel casting. It's a make-it-myself job, because nobody has one like it.

Cunning plan 1: Machine a pattern out of a chunk of aluminium.
Made a mess of it and it required too much work to rescue it. Also the spokes were tapered on one side as it needed to be a flat-backed casting to cast easily. Needs a lot of work on the eventual castings.

Cunning plan 2: Make a mould in aluminium, cast half of the pattern in epoxy, cast another one, and a nice easily-cast split pattern with radii on both sides of the spokes. Nice and easy to machine the cavity with a suitable angled cutter. Spray with silicone mould release agent, fill with epoxy, and cure at 100C in the cooker for an hour. Spend another hour chipping bits of epoxy out of the mould cavity. Repeat using Mr Sheen plus a quick burst of lacquer and it stuck even harder. Olive oil, WD40, room-temperature curing, all have the same effect. My shed is now covered in tiny bits of cured epoxy.

Is there a way of releasing epoxy from an aluminium mould?

[abby]

Hi Nigel , You did not say what size the wheel is or the material , as you have discovered epoxy resins stick in a metal mould like the proverbial to a blanket , I have the same problem releasing wax patterns from epoxy moulds , you will have success with silicone rubber , or urethane rubber which is a bit cheaper.
Pour the liquid rubber into your aluminium mould , when set it will pull out easily to give you your half pattern , then reverse the process to form a rubber mould of the rubber pattern , from which you can then make your epoxy pattern.
Bit long winded but certain to produce good results.
Alternately you could try pouring molten lead into your aluminium mould , drill a few well placed holes for ejector pins though , and this should also work well . If the draws are good enough for a sand casting then the lead should release easily and will have no shrinkage.
Abby.

[Nigel Bennett]

Thanks for that, Abby! My wheels are about 3.1/2" or 90mm diameter. I've located a chunk of LDPE in the recesses of my shed and I'm going to have a try with that for a mould. Nothing seems to stick to it! I've used 8 degrees as a draft angle, which ought to be enuff.

Your wheels look pretty good, I must say - if the LDPE (at the moment a cost-free option) proves a frost I'll probably try your method.