Sorry for the slow reply. I just got back from a missions trip to Mexico this week and have been a bit under the weather since.
riffdex, an armrest is too large to print on this machine. It would be much easier to buy an armrest off ebay or a parts car. The quality would be higher too.
nitro-nige, thanks. The urethane really isn't anything special. Its just a standard 2 part urethane. I got it from:
Casting Resins
I simply made a mold as shown, mixed the urethane, and poured it into the mold. I didn't vacuum it or anything.
I have a couple people interested in knobs. I'll be working on them as time allows. PM me if you are interested in something specific. I'm working on making a 1, 2, and 3 button version with different button types (toggle, momentary on, and momentary off) for each slot. However, next week I'll be out of state for work and won't be able to do any work on 3d parts.