Hy Stef,

I started making molds a few years back and have gotten quite some experience (both good and bad), so maybe a short intro into easy mold making (i mean durable molds for 100 parts +).

First i take a plastic sheeted piece of wood (like for bookshelves) and cut the contour of the object. The (waxed!!) object is placed into this cutout so that it protrudes exactly halfway. I tack it in place using that colored clay type of stuff the children usually play with. The seam all around is then filled with candle wax (light it and let it drip in, scratch off all the excess after it has cooled with a sharp knife).
Now drill a few holes and place steel rods in there.

Thats all the preperation.
Now you start laying up the mold. First apply a coat of mold surface resin (usually black or blueish) with a brush. Once this gets tacky, i cover everything with a thin layer of fibreglass cloth+epoxy. All the sharp corners and areas where bubbles could form are filled with epoxy goo (thickened with glass bubbles or similar)
Before it starts to cure i mix up a batch of laminating ceramic, sink the special fabric in there and just massage it onto the laid up epoxy. Walk away for 24 hours. Part 1 complete.

Now turn it around, take off the wooden plate (leave the steel rods in there!), clean it off and wax it again, and then repeat the procedure. When this side has cured, simply pull out the steel rods and pull the two haves apart.

With the rods you can always get the 2 pieces aligned just right, and you don't have to join them after taking them out of the molds. They will come out with just a very thin seam....
I buy all the stuff, especially the ceramic and the special "M1" fabric, at r&g : http://www.r-g.de/en/
I'm sure there's a supplier in the US as well. That stuff is cheap, as 1 layer will give you a mold approximately 6mm thick....enough for all molds up to 100"!

Hope this helps a bit....
best regards


PS: attached you will find 2 plugs for a rudder i just made (they were cnc milled)....after placing the part in the wood and drilling the holes it should look just like that.