Tubing or T Slot Razor Cutter

Nifty T slot razor blade holder to cut weatherstrip to fit an odd sized window

Add 1/4-20 thumbscrew and nut to adjust blade position
Two moderately strong springs to counter the thumbscrew and keep the blade position firm
two more 1/4-20 bolts to hold it all together
Two 9D finish nails used to center and hold the blade between the insterts

If you need it to be more accurate, you could thicken the inserts and make the body/chamber wider to accommodate

V5 has adjustable T slot width.