This is a specialized remix of Botmaster's excellent Razor Guillotine redesigned for cutting ptfe bowden tubes.
It produces a clean, square cut without any crushing of the tubing.
You will need:
2 4m 50mm hex head shoulder bolts
2 4m nuts
1 3m 15-20mm screw
1 3m nut
1 single edge razor blade
I can't give any specs on the springs because, like Botmaster, I used springs I already had from an assortment.
The CAD files could be modified to use different (non-metric) hardware pretty easily.
After printing the base I chased the tubing hole with a #19 drill. A 4mm or 4.1mm drill should also work. The size of the hole can readily be changed in the openscad file. If desired it could even be adapted for a bowden for 3mm filament.
The razor blade slides into the carrier from the side before assembly. The shoulder bolts are threaded in from the top, engaging the nuts in the bottom of the base. I added the Fence_knobs for two reasons. It makes assembly/disassembly easier when replacing the razor blade (which, considering you're only cutting ptfe, will be seldom if ever). More importantly, it also acts as a spacer so that the edge of the razor blade is never exposed.
Assemble the fence screw by placing a 3m nut in the recess and tighten a 3m screw from the other side. There should never be much torque placed on this part so there is little chance of this unscrewing in normal use.
If you customize this with the openscad design you'll need the origial base stl from Botmaster's original Razor Guillotine.