I've wanted to try resin casting for a long time, and have finally done so a few times in the last three days. It's never been easier to do before, thanks to my easy access to CNC mills. Once I become proficient at this, I'm mainly interested in making two-sided molds for producing complex parts that would be hard to make otherwise, and casting with materials that would be difficult to machine (like soft rubbers).
I've made three silicone molds and casted two parts in the resin from one of those molds (see above). One side of the parts (the side that was in the bottom of the mold) look great, but the top is full of air bubbles. There are a few things I hope to improve in the process soon.
I used a prototype Othermill Pro to mill out the patterns for each silicone mold in machineable foam. This made quite a mess, but the mill didn't have a problem. The material itself isn't ideal - I hope to try something different soon. I think I can find something with a better surface finish.
Here's what the setup looks like. Not pictured: gloves, mold release spray, popsicle sticks and a scale. For the silicone molds, I'm using Quantum Silicones QM 262, based on suggestions in the fantastic Resin Casting guide by Michal Zalewski. It has a long pot life, so it's easy to work with - this gives you plenty of time to adequately stir the mixture (important!) and properly degass it in the vacuum chamber.
I'm still working on releasing silicone molds from the machineable foam in a less destructive manner.. this was my second attempt at a mold, now in a more complex pattern - these are Bit Fans, which are used for chip clearing on 1/8"-shank endmills. Note that two of the female Bit Fan molds are missing the main column in the center, due to air bubbles.
Closeup on the Bit Fan mold. I was pleasantly surprised by the amount of detail from the machining that was picked up by the silicone.
My first few days went better than expected, but there are definitely improvements to be made. The resin I'm using is the very well-rounded Innovative Polymers IE-3075, which has a fairly short pot life of 8 +/- 2 minutes. With the low volume of resin I've been mixing at a time, I try to wrap up in faster than 6.5 minutes.
Things I hope to change, in order of priority:
Acquire a better vacuum pump. I think the one I'm using was broken and (maybe?) repaired in the past, but it isn't doing well. And with the cheap chamber I'm using, I simply can't degass resin fast enough.
I need a more accurate scale for weighing things.
Find some dedicated sheets of plastic, that have been faced flat, and smaller weights to help set up the resin parts after casting. The material I've been using thus far hasn't been flat enough, which can cause air bubbles.
Start blanketing the bottles with canned air to better preserve them over a long period.
I feel the need to reiterate that 99% of what I've learned so far has come from the fantastic guide by Michal Zalewski. Highly recommend.
More soon, I hope!