The mechanical XY system I'm looking at has a 1:2.5 step down to the motion belts. Everything I've seen prior has an integer ratio 1:2, 1:3, 1:4. Seems to me the half ratio will make it more difficult to define steps per mm in the controller. 1.8 deg/2..5 = .72 deg steps. I have no experience that tells me what affect that will have versus every thing else I've seen that is a multiple or divisor of .6 deg.
All you have to do is reprogram the number of steps per inch or cm and the software will take care of everything. I recently swapped out acme screws with ballscrews on my CNC router. The acme screws had 10 threads per inch which worked out to exactly 4000 steps per inch with steppers on my machine. The ballscrews have 2 threads per cm so I had to re-program Mach with 1968 steps per inch. Sometimes Mach will show XY coordinates like 1.0002" instead of 1.0000" because it cannot hit the exact position requested. It gets as close as it can. I have about 0.001" of backlash, so I am not really worried about the very small positioning error.
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Using reduction on stepper output
