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      Steps per Millimeter (Steps/MM) in Laser Machines

      Calibrating Steps/MM for Accurate Laser Cutting and Engraving

      If your laser output appears stretched or squished in any direction, the Steps/MM settings may be incorrect. This essential setting ensures precise movement of your laser machine and accurate cuts or engravings.

      LightBurn includes a Calibrate Axis Tool to fine-tune these settings, but understanding how Steps/MM work can help you diagnose and correct issues manually.

      What is Steps/MM?

      Steps/MM is the number of motor steps required to move the laser head one millimeter. This value depends on:

      1. Stepper Motor: The motor’s step angle and configuration.
      2. Motion System: Components like belts or lead screws.
      3. Microstepping: Subdivisions of a motor’s natural steps for finer movement.

      Stepper Motor Basics

      Stepper motors move in discrete steps rather than continuous motion. For example:

      • A motor with a 1.8° step angle completes one full rotation in 200 steps: Screenshot_148

      The machine translates these steps into linear motion based on the motion system configuration.

      Motion System Configurations

      1. Belts and Pulleys

      • Common in small diode lasers.
      • Example setup:
        • Motor: 1.8° Nema 17 stepper motor.
        • Belt: GT2 (2 mm pitch).
        • Pulley: 20-tooth GT2.
      • Calculation:
        • 20-tooth pulley moves 40 mm per full rotation: Screenshot_149

      2. Lead Screws

      • Used in machines like 3018 CNCs.
      • Measure the pitch (distance traveled per full screw rotation).
      • Example: A 2 mm lead screw pitch means 1 rotation moves the laser head 2 mm.

      Microstepping: Enhancing Precision

      Microstepping divides each natural motor step into smaller sub-steps, dramatically increasing resolution.

      • Example: 1/16th microstepping increases steps per rotation from 200 to 3200: 
        Screenshot_150
      • Benefits:
        • Smoother motion.
        • Higher resolution:
          Screenshot_152

      Finding Your Steps/MM

      1. Check Manufacturer Settings

      • Start with the machine’s manufacturer for exact specifications.

      2. Identify Motion System Components

      • Motors: Most are 1.8° stepper motors. Look for specifications on the motor body or datasheets.
      • Belts: Measure the pitch (e.g., GT2 = 2 mm).
      • Lead Screws: Measure pitch by tracking a single thread for one rotation.
      • Microstepping: Check driver configurations (e.g., DIP switches or jumpers).

      3. Use a Stepper Motor Calculator

      Tools like online calculators simplify calculations for steps/mm based on your setup.

      Calibrating Steps/MM in LightBurn

      If the machine’s movement is close but needs adjustment, use LightBurn’s Calibrate Axis Tool:

      1. Access the tool in LightBurn.
      2. Enter the commanded and measured distances.
      3. LightBurn calculates the corrected Steps/MM value.

      Microstepping Configuration

      Check your controller for microstepping settings. Common driver configurations:

      • Example: DRV8825 settings:
         CFG1  CFG2  CFG3  Microsteps
         Open  Open  Open  Full step
         Closed  Open  Open  ½ step
         Open  Closed  Open  ¼ step
         Closed  Closed  Open  ⅛ step
         Open  Open  Closed  1/16 step
         Closed  Closed  Closed  1/32 step

      Open/Closed refers to jumper positions or DIP switch states.

      Summary

      Steps/MM is critical for precise laser movement. By understanding your machine’s motion system, motor configuration, and microstepping settings, you can ensure accurate laser operation. Use tools like LightBurn’s Calibrate Axis Tool and online calculators to fine-tune your setup.