timing belt and pulley

[Web Goblin]

I would bore out the pulley and broach it for a key. Also drill and tap above the keyway for a grub screw. I would because ive just done it for 4 pulleys for nema 34s.
The only problem I had was that I bought a spare nema 34 a while ago just in case I needed one. All bought from zap and all have the same part numbers. The only difference was that the new one has a smaller shaft diameter than the older ones. No prizes for guessing which shaft I measured before I made the broaching socket, drilled the pulleys and cut the keyways.
Ah well at least a smaller hole can be bored out.

[Tom J]

Personally I use only HTD pulley - mostly 5M - 15mm wide. I used to try T5 and was not happy with backlash.
As Boyan explained number or teeth matters, so my smallest pulley has 15 teeth. Ratio:
15-20=0.75
15-25=0.6
15-30=0.5
15-40=0.375
15-50=0.3
15-60=0.25
I never use bigger pulley than 60t due to size.
for bore start from 10mm I use broaching tool with key way 2mm wide. Biger bore wider key way. For 1/4" =6.35mm I drill and tap grab screw - start from 3mm for 15t - see photos