Welcome to the CNCZone. I assume you've checked the MACH3 manual pages 5-10 through 5-13 and found them a bit confusing? (
http://www.machsupport.com/docs/Mach3Mill_1.84.pdf)
Maybe this will be helpful: (maybe not - but gives you something to think about)
(
STEPS per REV)*(
THREADS per unit)*(1/(
Controller Stepping FACTOR))
STEPS per REV for your 1.8 degree motor this is 200 (A most common setting for many Stepper Motors)
THREADS per unit For Imperial threads: pitch is 1/TPI -Threads per Inch. But in the above solution you'd use TPI. Your mileage may vary with the mms.
Controller Stepping FACTOR for Full Step = 1; 1/2 Step = 2, 1/4 Step = 4; etc
Then, MACH 3 also has a means to calibrate the axis to fine tune your system - see page 5-13.
Hope thats helpful -
Jim
ger21 has a nice answer of two here on the site - too. You'd need to wait for his response - or do a search