Key takeaways
Ball screw wear rarely announces itself. It creeps in as slowly growing lost motion until a part fails inspection or the control throws a following error alarm. This guide is for maintenance technicians, managers, and plant engineers who need to confirm whether a CNC axis problem really is the ball screw, and decide what to do next.
A ball screw converts servo motor rotation into linear motion through recirculating steel balls that roll between hardened grooves, called races, on the screw shaft and inside the nut. Rolling contact keeps friction low and efficiency high.
Precision comes from preload: a double nut arrangement or slightly oversized balls keep the balls pressed against both flanks of the race, removing clearance and adding stiffness. As balls and races wear, preload fades first, then true clearance appears. That clearance is backlash: the table no longer moves the instant the screw reverses.
Several of these signs overlap with drive and feedback faults, so keep servo motor failure symptoms and encoder failure symptoms on your differential list before condemning the screw.
| Symptom | Likely cause | First check |
|---|---|---|
| Reversal spikes in ballbar plot | Backlash from wear or lost preload | Dial indicator backlash test at that position |
| Sloppy mid stroke, tight at ends | Wear concentrated in the working zone | Compare backlash at several stroke positions |
| Grinding or clicking while jogging | Ball or race damage, contamination, dry screw | Inspect wipers and lubrication, listen along the full stroke |
| Sudden backlash after a crash | Brinelled races or damaged thrust bearing | Check thrust bearing float and coupling before blaming the screw |
| Dimensional drift over a shift | Thermal growth of the screw | Compare cold and warm positioning checks |
Before any hands on check, apply lockout/tagout and respect stored energy: a vertical axis can fall when its brake is released, counterbalance cylinders hold hydraulic or pneumatic pressure, and chain counterweights hold tension. Never bypass interlocks or safety circuits to jog an axis with covers open; use the machine's approved setup mode.
Uniform backlash along the whole stroke points at thrust bearings, the coupling, or overall nut preload. Backlash only in the busy zone means the screw itself is worn there. Note the active backlash compensation values before testing, because compensation hides part of the lost motion.
A ballbar circularity test shows backlash as reversal spikes at quadrant changes and takes minutes to run, which makes it ideal for trending. A laser interferometer maps error along the entire stroke: a worn zone appears as a widening gap between forward and reverse passes, and the same data rebuilds the pitch compensation table after repair.
Jog the axis over full travel at moderate feed and listen for zones of grinding or clicking. After several minutes of cycling, check the nut and bearing housings with an infrared thermometer: a nut running clearly hotter than the rest of the axis suggests dry running, over tight preload, or misalignment.
Backlash compensation inserts a small extra move at every axis reversal. For small, even wear it restores acceptable behavior, which is what it is designed for.
It cannot fix what it cannot see. A single value cannot correct position dependent wear: tune it for the worn middle and the machine over corrects at the ends. It also cannot restore preload stiffness: under cutting load the axis is still pushed through the clearance, so finish and accuracy suffer even when a cold reversal test looks fine. Treat rising compensation values as a wear trend worth logging, not as a fix.
Put these tasks on a formal preventive maintenance schedule alongside the checks in our CNC spindle maintenance guide: the same discipline protects both.
Every scrapped part, alarm stop, and unplanned backlash adjustment on that axis is a downtime event. Log each one with a specific cause code (for example, axis backlash) instead of a generic mechanical fault, and track MTBF and MTTR for the asset. Quarterly ballbar results and compensation values belong in the same history.
Do this and chronic wear stops hiding inside availability and quality losses. The trend data justifies the engineering fix, a nut replacement or an alignment job, before the axis fails mid shift. That is the difference between reacting to breakdowns and managing OEE in manufacturing deliberately.
Backlash grows in fractions of a millimetre, but its cost shows up as micro stops, rework, and slow cycles that rarely make it into a manual logbook. Fabrico is computer-vision-verified OEE plus closed-loop maintenance execution: cameras catch stops and micro-stops that manual logs and sensors miss, and maintenance work orders close the loop from detection to fix. If a worn axis is quietly taxing your output, book a Fabrico demo and see what your machines are really doing.
There is no universal number: it depends on the machine class, the work, and the builder's specification. A healthy preloaded axis measures close to zero. What matters most is the trend against the machine's own baseline, measured at the same positions each time.
Grinding, clicking, or a dull rumble while jogging, often only in one section of travel. A smooth whir along the whole stroke is normal; localized noise is not.
Often, yes. If the shaft races are still in good condition, replacing wipers, restoring lubrication, and adjusting or replacing the preloaded nut can bring the axis back within specification.
No. It masks small, uniform lost motion at reversals but cannot restore stiffness or correct wear that varies along the stroke. Rising compensation values are a signal to plan mechanical repair.
Life varies enormously with load, speed, lubrication, and contamination. A well lubricated, well sealed screw can run for many years, while a screw running dry or full of swarf can fail in months.
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