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Leadscrew Backlash Basics
Guide · Updated October 28, 2026
Backlash is the lost motion between the leadscrew and its nut. Turn the handwheel one way and the table moves; reverse it and the dial turns a few thousandths before the table follows. Every manual machine has some; the trick is knowing how much and working around it.
Measure it
A dial indicator on the table measures real movement. Check the indicator with gage blocks if you rely on it. The free Gage Block Calculator builds the stack.
Step by step
- Lock the other axes: Lock the axes you are not testing and leave the gibs normally snug.
- Mount an indicator: Put a dial indicator on a magnetic base against the table or carriage.
- Take up the slack: Move the axis in one direction past where you start, then stop.
- Zero both: Zero the indicator and note the handwheel dial reading.
- Reverse slowly: Turn the handwheel the other way until the indicator just starts to move.
- Read the backlash: The handwheel movement before the indicator moved is the backlash.
- Repeat along the travel: Check at both ends and the middle; screws wear most where they are used most.
Worked example
On a knee mill X axis, the handwheel turns 0.009 in on its dial before the indicator moves when reversing in the middle of travel, and 0.005 in near the ends. Backlash is about 0.009 in where most work is done. To hit a dimension, always finish moving in the same direction, for example always approaching from the left; if you overshoot, back up past the mark by more than 0.009 in and come back in.
Adjusting backlash
Many mills have a split or adjustable nut. Tighten until backlash is about 0.002–0.004 in with no binding at the ends of travel. If it is tight at the ends and loose in the middle, the screw is worn and needs replacing.
Climb milling and backlash
With backlash, a climb cut can pull the table forward into the slack and grab the cutter. On manual machines, use conventional milling, lock the table axis you are not moving, and use the table locks lightly for drag on finish passes.
Tips
- DROs: A DRO reads the table, not the screw, so backlash does not affect the reading.
- Tramming: tramming a mill.
- Indicators: magnetic base indicator setup.
FAQ
How much backlash is normal?
About 0.002–0.005 in on a well-adjusted manual mill; worn machines have more.
How do I measure backlash?
Reverse the handwheel and see how far it turns before a dial indicator on the table moves.
Does a DRO fix backlash?
No, but it shows true table position so you can work around it.
Why is climb milling risky with backlash?
The cutter can pull the table into the slack and grab.
Can I eliminate backlash?
Ball screws nearly do; on acme screws you can reduce it with an adjustable nut.
Related guides and calculators
- How to Tram a Mill
- Magnetic Base Indicator Setup
- How to Use a Dial Indicator
- How to Drill on a Mill
- How to Face Mill
- How to Use a Rotary Table
- How to Indicate a Fixture
- How to Cut Metric Threads on an Inch Lathe
- Digital Readout (DRO) Basics for Machinists
- How to Set Up a Horizontal Mill
- All free machinist calculators
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