Machine Accuracy After Relining: Positioning and Repeatability Checks

A successful guideway relining is measured by machine behaviour after the repair, not by the liner alone. A new PTFE-based running face can reduce low-speed friction and help restore worn geometry, but ball screws, encoders, servo tuning, thermal movement and workholding also affect the final result. Use a documented before-and-after record so the repair decision is based on measured change rather than a visual impression.

Positioning accuracy and repeatability are different

Positioning accuracy describes how closely an axis reaches a commanded location. Repeatability describes how consistently it returns to that location over repeated approaches. A machine may repeat well but miss the commanded point because of a scale or calibration offset. It may also reach the correct point once and repeat poorly because friction, clearance, backlash or uneven contact changes with travel direction.

Build a before-and-after measurement record

• Record the machine, axis, travel direction, ambient condition and measurement instrument before dismantling the way.
• Measure several positions along the usable travel, including both ends and the normal working zone.
• Repeat the same approach direction, then test reversal so backlash and friction are not hidden in one average value.
• After relining, repeat the test with the same setup, speeds, lubrication condition and warm-up procedure.
• Keep raw readings beside the calculated error, repeatability spread and notes about adjustments.

What improved motion should look like

Low-speed handwheel or jog movement should be smooth through the measured travel rather than tight in one zone and loose in another. Repeated approaches should settle consistently without a jump at the same location. The slide should maintain contact without excessive gib pressure, and the final centre height, parallelism and squareness should agree with the repair record. Way oil must reach the intended contact area and the wipers must keep chips away from the liner edge.

If the repaired way uses Blue TEBAK slideway liner, Green TEBAK slideway liner or another colour in the same family, the test method remains the same; colour is not an accuracy grade. Review the stick-slip guide to separate low-speed friction symptoms from control-system issues, and use the slideway liner load and pressure guide to relate contact footprint to compression risk.

When the result does not meet expectations

Do not add thickness or tighten the gib to hide a poor result. Compare the full-travel error map, contact pattern, oil coverage, centre height and reversal behaviour. A local high spot, incorrect reference, contamination, uneven adhesive layer or distorted mating member can create a repeatability problem that a thicker liner will not solve. If readings change after warm-up, repeat the test at the machine's normal operating condition before deciding on correction.

Frequently asked questions

• Does a new PTFE liner guarantee better positioning accuracy? No. It can improve guideway friction and geometry when correctly fitted, but positioning also depends on the drive, feedback, thermal state, alignment and calibration.
• Why can repeatability improve while positioning remains offset? A smoother, more stable guideway can reduce variation between repeated moves while an existing calibration or scale offset remains.
• Should accuracy be checked immediately after bonding? Check only after the adhesive has cured, the liner has been finish-machined and the machine has reached the agreed test condition.