Hi John,

thought so too, but then I did some calcs and it doesn't seem to leave a lot if you put a keyway:

- outer dia of the pulley is 24.32mm, r=12.16mm. HTD5 belt is 2.08mm deep, I'm guessing same is true for the pulley teeth, which means the internal 'meat' on the pulley is 12.16mm - 2.08mm = 10.08mm radius

- keyway in the shaft is 5mm wide, 3mm deep, spec says (found somewhere on the web) to cut a 2.3mm deep keyway in the pulley

The above means a keyway cut in the pulley will leave 10.08mm - 7mm (shaft radius) - 2.3mm = 0.78mm of material.

Unless of course I'm cocking it up somewhere.

Grub screw in the toothed area will give me roughly 3mm thickness for the grub screw to hold on to. Probably enough but as you say not plenty for a lot of torque.

Regards,
dsc.