Well, with a bit of ballast, that little unsupported blade actually did cut some vinyl:
That ugly nut adds 125 g to the pen holder’s 19±10 g (that’s the spec) down force and grossly overloads the pen-lift spring at the solenoid, but it did provide enough force to carve that little strip from the vinyl sheet. Vertical compliance comes from the pen holder’s travel, so the weight exerts a constant force at the knife tip.
I’m using the front-panel controls to drive the pen around at whatever speed the FAST button provides, which limits the results to straight lines.
The vinyl, leftover from a discarded window decoration, is 0.15 mm = 6 mil thick and definitely not intended for use with a cutter; vinyl cutter sheets and rolls seem to run around 0.07 mm = 3 mil.
Obviously, this doesn’t have much potential, but it actually worked better than I expected. The unguarded blade bites into the substrate (which I did expect), so the next step is to wrap a nose around the blade for controlled depth-of-cut.