This RTV is mixed by measuring 10 parts A with 1 part B. 120 grams A with 12 grams B, to make 132.0 grams. This scale weighs in 1/10 gram increments. The manufacturer makes a big deal about accurately weighing parts. After mixing the RTV must be vacuum degassed. This shows our vacuum bell. The material expands about 3 times in volume during vacuuming. We are able to demold in about 4 hours. The second side, which is the bottom of the mold is poured next. Both a sealing agent and mold release are sprayed on the top half of the mold and allowed to dry.

This stuff cuts like butter. Here we cut sprues and vents into the mold. The vents must be quite fine, just enough to let gas escape. Notice the fishbone cut. We used jewelers talc put in cloth from an old t-shirt. The talc bag is padded on both molds and excess tapped off.

Pewter at 550 degrees F is being added into the pouring spout while the caster is spinning at 300 rpm. The photo on the right shows the casting as it comes out of the mold with the sprues and center button still attached. The rings on the aluminum plate give me an idea where to center. Notice the talc still in the mold.

Thanks for looking

Our next trials will be with larger items in larger molds. This caster can handle molds up to 11" in diameter by 2 1/2" thick Vulcanized rubber molds, compared to RTV (room temperature vulcanizing), are considerably less expensive, last longer and take only 1- 2 hours to produce. Ah, so many projects, so little time . . .