X&Y 9MM GT3 Belt Upgrade

The stock idler pulleys are for 6mm belts.
Do you will need to order 9mm ones.
EDIT: This is Adam’s first link in his post! LOL

Oh my mistake. Thanks for the link. I just ordered 6 of them.

I replaced the belts on my Y axis with GT3 6mm belts. I have not put it to a heavy load test, but with hand pressure the motors will slip before the upgraded belt will.

I’m right about to do this upgrade. how does one re-calibrate the motion controller once the belting and pulley is swapped?

For X and Y, you have to update these GRBL parameters
$100 (x, step/mm)
$101 (y, step/mm)

Your Z
$102 (z, step/mm)
is not affected by belt pitch, as long as the gearing ratio remains the same.

Back to X & Y, the $100 & $101 values are expressed as


S: your motor’s steps per revolution (200 for the stock motors)
M: microsteps (8 by default for X&Y)
T: pulley teeth (20 for the stock pulley)
P: belt pitch (2mm for GT2, 3mm for GT3)

So assuming you only change the pitch on X & Y, your $100 & $101 should update from

(200step/rev * 8microstep/step) / (20teeth/rev * 2mm/tooth) = 40microstep/mm


(200step/rev * 8microstep/step) / (20teeth/rev * 3mm/tooth) = 26.667microstep/mm


This is an old thread and I’m sorry if my reply bothers anyone. Just a word of warning to anyone buying belting from Powge. The belt actually looks fine (haven’t used it yet), but the pulleys I bought from them are far from concentric. There is a +0.2 mm wobble to them, which will of course transfer to unwanted movement of the spindle. And one of the pulleys has so rough bore that it cannot be installed without honing it a little. As the saying goes, buy cheap, buy twice. I have to install and use these for a little while, but I have already ordered genuine Gates belting and pulleys.

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Has anybody used PU belts instead of rubber? I read that PU is much better than rubber.

And can anyone report on the steel-reinforced belts over the fibreglass?