# Bought wrong 20 teeth pulleys

Just got my mpcnc up and going as a router, using Aspire as the cad. (In my daily job I use Aspire + Mach3)
But all my cuts were faster and bigger on the x + y axis. At first I thought it was from converting inch to mm in aspire. But now I see that i used 20 teeth pulleys instead of 16. Whats the best way to recalibrate my mpcnc? Whats a good steps/mm to start with? Thanks,

I’m going to have to reflash my arduino. Theres no way I’m turning that knob every time. my steps/mm was 200.I turned it down to 180.00 on the x and y. And its still big. I’m ordering the correct 16 teeth pulleys. But I want to play with it now. I’m off work for a long weekend. Might have to use one of those 20 teeth pulleys and an extra stepper + arduino to adjust the knob. Just kidding, I dont know the formula to find the correct steps/mm. just keep turning it down till it gets the right size. Thank you creator of the mpcnc!

and changed this line in the arduino

#define DEFAULT_AXIS_STEPS_PER_UNIT { 200, 200, 4535.44, 200 } //MPCNC
to

#define DEFAULT_AXIS_STEPS_PER_UNIT { 150, 150, 4535.44, 200 } //MPCNC

Its good enuff for the girls around here to play with. until I actually measure the movement. or get the 16 teeth pulleys. Thanks. Now I just need some help making room for the 4x8 lowrider.

I usually use the prusa calculator to find the right steeps x mm.

Are you sure that yours it’s 150 steps x mm?
If you use 1/32 microsteping, 1.8º motors, and gt2 with 2mm pitch, it should be 160 steps to travel 1 mm…

Thanks Martin DB, I changed #define DEFAULT_AXIS_STEPS_PER_UNIT { 160, 160, 4535.44, 200 } //MPCNC line in the configuration.h file. Reflashed the arduino. But my mpcnc lcd still says 200 steps/mm. Im not cutting anything that has to be dimensional correct. I’ll just scale down the size and feedrate in Cad, untill the mailman brings me the 16 teeth pulleys.