# CNC stepper motors are loud and slow after decreasing the steps/mm from 250 to 5

I'm making a drawing robot and have hooked up my steppers to each axis. I'm using the grbl shield with arduino and nema 17 steppers.

Initially the firmware was set at 250 steps/mm but with my setup this would move my axis by 50mm. Therefore I only need 5 step/mm. However now that I have put it to 5mm my steppers run very slowly and vibrate quite a bit.

This is the case even when I command an axis to move a set distance. For example, with 250steps/mm I can tell the axis to move 2mm in universal gcode sender (actually 100mm physically) and it will move swiftly and quietly. However with the setting at 5 steps/mm I can command it to move 100mm and it will be very slow, loud and vibrate like hell. This behaviour is seen even without changing any feedrate, max acceleration and speed settings.

Any ideas how I could fix the issue? Is 5 step/mm reasonable? I'm just using standard T-20 belts and pulleys so other people must also have this setting.

• Welcome to Robotics, Stephen. You said, Initially the firmware was set at 250 steps/mm but with my setup this would move my axis by 50mm. I don't understand why a steps-to-distance ratio is limiting your motion. At 250 steps per millimeter, you should be able to go any distance, it just requires lots of steps. Is there some other limiting factor here, like overflow or underflow of encoder counts? Can you link any datasheets for the components you're using or a video of the behavior you're experiencing? I can't tell why you're wanting to move from 250 steps/mm to 5. – Chuck Nov 20 '18 at 16:53