After a fair bit of work I finished making my aluminum mold. The mold parts fit together with almost no gap. It is actually difficult to take them apart if you don't pull perfectly straight. The upper and lower half are aligned by 4 dowel pins. I think two would have been enough, and might make it easier to open the mold. The insert that holds the pins also has dowel pins holes drilled. I was not sure if I would need dowel pins to align these parts. So I drilled the holes but waited to press the pins in. Turns out that you don't need them because of the geometry of the insert. Everything is held together with two threaded knobs. You can hand tighten the knobs and none of the resin leaks out. This was a huge improvement over my old rubber band method.
The controller for the heating is a simple arduino with a solid state relay and thermocouple module. I have them mounted up in a case and plan on making it a nice project box with a display and the ability to control 3 channels. The box is big enough for 3 solid state relays, the arduino, the thermocouple modules and power. I used a old iphone charger to convert the 110v AC to 5v DC. The front of the case will have banana plugs to connect the heaters, panel mount thermocouple jacks, and a display to show the temperature. It should be handy for several future projects. A few that come to mind are my reflow oven, anodizing equipment, sous-vide cooking, or basically anything else I want to control. The Arduino has some PID libraries that I plan to use. But for now it is just a simple look that checks temperature. If the temp is above my set point it turns the SSR off, if the temp is below it turns it on. The loop fairly fast (about 250 milliseconds) and keep the temp within 2 degrees of 150 degree F. There is a fuse 3.15 amp fuse on the power coming into the box just to keep things safe. It heats up very quickly about 90 seconds or so. This allows me to remove the resin from the mold after about 1 hour instead of 4-5 hours. The parts are not fully cured and it takes up to 7 days to reach full strength. But being able to remove them from the mold means I can cast more parts.
Here are some pictures.