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Backlash Compensation

Backlash is the lost motion or "slop" in a mechanical system caused by gaps between mating parts (e.g., a lead screw and nut, or loose belt teeth).

When an axis reverses direction, the motor turns for a brief moment to take up this slack before the load actually moves. This results in:

  • Circles that are slightly flat at the quadrants (ovals).
  • Undersized features.
  • Poor surface finish.

The Golden Rule: Fix Mechanics First!​

Software compensation is a band-aid, not a cure. Before enabling compensation:

  1. Belts: Ensure they are tight (like a guitar string).
  2. Couplers: Check for loose set screws on motor couplers.
  3. Anti-Backlash Nuts: Adjust or replace worn anti-backlash nuts on lead screws.
  4. Pinions: Ensure rack-and-pinion gears differ mesh properly.

Measuring Backlash​

To configure compensation, you must first measure the exact amount of backlash on each axis.

Method: Dial Indicator (Best)​

  1. Mount a dial indicator against a solid block on the axis.
  2. Zero the axis and the indicator.
  3. Move the axis away (e.g., G0 X10).
  4. Move the axis back to zero (G0 X0).
  5. Read the indicator. The potential difference from zero is your backlash (repeat 5 times and average).

Method: Test Cut​

  1. Cut a 20mm circle.
  2. Measure the diameter across X and Y.
  3. Calculate the difference between the expected diameter and the measured diameter.

Configuring Compensation​

Note: Backlash compensation must be enabled in your firmware build (#define BACKLASH_COMPENSATION in my_machine.h). If these settings don't stick, you may need a firmware update.

Settings:​

  • $160: X-axis backlash distance (mm)
  • $161: Y-axis backlash distance (mm)
  • $162: Z-axis backlash distance (mm)

Procedure:​

  1. Enter your measured backlash value (e.g., $160=0.05 for 0.05mm of slop).
  2. Run a test circle.
  3. Adjust until the circle is perfectly round.

Tip: Be conservative. Compensating too much can cause jerky motion or "clunking" sounds.

Conclusion​

You have now completed the core machine calibration! Your machine is:

  • Accurate (Steps/mm)
  • Fast & Smooth (Motion Tuning)
  • Oriented (Homing)
  • Precise (Backlash Compensation)

What's Next? Explore our Advanced Guides, such as Probing or Auto Tool Changers.