Hi fell over this thread when surfing
Poly Vee pulleys have the grooves cut at 40 degrees 2.34 mm pitch.
BSP is 55 degrees pitch this will make for a very poor contact.
Eric agreed but the belt is rubber and soon adapts.
Back in 1999 I built a pencil sharpener and the cutter ran on poly vee belt, 3;1 step up ratio from a 3,000 rev motor so the spindle does 9,000.
Now don't laugh about it being a pencil sharpener, it sharpens 7,000 per hour and was part of the millennium display in the dome in 2000.
Been running ever since, about 6 hours a day, 5 days a week, so far it's got thru 4 belts and one set of pulleys.
I always think proof is better in practice.