¹⁄35

Mold Making and Resin Casting

Now we will pour resin into both of the molds that we made earlier. Form a pour spout in the plastic cup that you will pour from and carefully fill the mold(s) with resin (Fig 30). In certain situations, for example, if you have a part that runs long horizontally, you may want to make 2 pour spouts instead of one to insure that the mold gets completely filled. A turkey baster works really well for pumping resin into hard to reach areas of a closed mold. You will know they are filled when you see resin come back up through both the vent and the pour spout.

If you have a pressure pot, put the molds in now and pressurize to 60 psi. A pressure pot works by "squeezing" the air bubbles so tight, they are microscopic, and thus you get cleaner castings.

Warning: Never try to make a pressure pot out of homemade items such as a pressure cooker. Only a pot rated for this psi should be used and it needs to have a locking lid.

A home made pot with an improper psi rating can explode, sending shrapnel in every direction, causing serious injury and yes, even death!

I have found that if you plan your pouring and venting system carefully, you will only need a pressure pot for the most complex, detailed parts, and even then, it is not necessary, but expect to do a little filling of air bubbles. Here is a tip for filling air bubbles and pinholes. When I get air bubbles that need filled, I usually put that part aside until I make another pour. After you do this, you will have some resin still in the bottom of the pouring cup. Wait until this gels and using a stirring stick as a spreader, fill the holes in the affected piece.

Once poured, you will see, in about 5 minutes, what we call the "bloom". That is the catalytic reaction between the 2 parts, which causes the resin to harden. You will know that you mixed your resin properly when you see this (Fig 31).

After 30 minutes, you can remove the parts. Remove the rubber bands and support pieces and separate the 2 halves on the 2 part mold. Gently flex the piece and it will pop right out. On the single part mold, I usually apply a little upward pressure with my fingers from the bottom of the mold to loosen the parts up (Fig 32).