Just a simple enough cross cut sled to cut 90° angles on your Proxxon ThermoCut.

Needs supports to print because of the overhangs. 

You might have to play around with the scale to get it to fit well. The part which slots into the side slot of the proxxon has a 0.2mm clearance. Depending on your printer this could be too tight or too loose. Make sure it fits well without a lot of play, but loose enough so it can slide easily in the track.

The 45° technically works, but it slightly fiddely to use. If people are interested I might model a better angle cutter.