X axis calibration

[Simon_Johnson]

I need to calibrate my X axis. I would like to use a formula so that I can be within the tolerances of the belts themselves. I used an online calculator at RepRap Calculator - Original Prusa 3D Printers, and that worked for my Y axis, but the problem is, my X axis contains two pulleys, 1 with 18 teeth (On the motor itself) and the rest of the gantry at 20 tooth. How can this be worked out?

I’m using GT2 belt and pulleys and the 1/32 DRV8825 driver. Also, the Ultimaker gantry within my CTC printer (makerbot chassis).

Y axis is set at 160 steps per mm, and it’s perfect.

[Simon_Johnson]

Edit:

I came up with a formula, but I’m not sure how accurate it is.

(200 X 16) / ((18 + 20) - (20 / 18 X 2)) X 2 = 178.8819875776286