For a while I've been pondering the problem of getting a bag into the tube and I think I've decided on something that works. The bag will initially be inserted, at least partially, into a short length of tube branching off the main cylinder. A push rod of just the right length will be used to push the bag the rest of the way in. When the rod is fully inserted, the bag will be completely in the main cylinder. I think a picture is needed here.

I've also figured out a piston. I got a length of steel pipe that fits inside the main cylinder with about 1mm of play. On the end of this pipe I will weld a thin disc that is machined to fit snugly in the cylinder. I don't want it too snug because I want air to escape around it, but it needs to be snug enough to keep pressurized plastic inside.

Code uploaded

It's not much, but the code I have for the induction heater controller is up on the git. It will surely be updated and merged into the main device controller code eventually, but here it is if you're interested.