Diagnostic Guide
Uneven Guideway Contact Pattern: Diagnose Pressure and Alignment Before Relining
An uneven contact pattern across a machine-tool guideway is evidence about load transfer, geometry and lubrication, not a thickness specification by itself. This diagnostic guide shows how to record where contact is high or missing, separate alignment problems from liner problems, and prepare a measured repair brief before bonding new PTFE slideway material.
What an uneven pattern tells you
A contact check that marks one end heavily and leaves the other end almost clear means the slide is not transferring load uniformly. The cause may be taper, a hollow or crowned way, a distorted gib, incorrect assembly or a lubrication path that changes friction during the test. The pattern is useful evidence, but it is not proof that the liner alone is worn out.
Record the pattern before changing anything
- Clean the mating faces and remove loose oil, chips and old marking residue without altering the reference surfaces.
- Mark the travel direction and divide the contact length into repeatable stations from one end to the other.
- Apply a thin, consistent film of TEBAK Tuschierpaste to the reference face and bring the members together without forcing a tight gib.
- Separate the members in the same direction each time, photograph the marks and note heavy, light and missing contact zones.
- Repeat after the slide is moved to another travel position so a single local mark is not mistaken for full-length bearing.
Separate contact, geometry and lubrication causes
| Observed pattern | Likely direction for investigation | Evidence to collect |
|---|---|---|
| Heavy at one end, light at the other | Taper, misalignment or uneven gib pressure | Straightedge/indicator readings and gib condition |
| Narrow bands with gaps | Local high spots, scoring or debris | Surface inspection and repeat contact map |
| Pattern changes after oiling | Interrupted supply or contaminated oil film | Groove continuity, metering and wiper checks |
| Uniform marks but rough low-speed travel | Friction, servo or adjustment issue rather than bearing area | Slow traverse, reversal and lubrication observations |
Do not size the liner from the darkest mark
The darkest contact spot shows where the members touch under the test condition; it does not define the finished liner thickness or the load capacity of the repaired way. Measure the removed material, original centre height, bearing footprint and available machining allowance. Then review the slideway liner load and pressure guide before selecting a thickness and the skived PTFE slideway sheet guide before approving the bonding face.
A practical repair brief
- Machine and axis identification, travel length and load direction.
- Contact photographs or a station-by-station map showing heavy and missing marks.
- Measured taper, flatness, parallelism, centre height and gib condition.
- Oil type, groove layout, wiper condition and whether the pattern changes after lubrication.
- Required liner colour, width, finished thickness, machining allowance and total length.
TEBAK supplies the PTFE-based running material in Blue, Green, Brown and Brick Red. Colour is a workshop identifier; the repair decision still depends on measured geometry, the load path and a clean, prepared bond surface.
Acceptance checks after relining
After the liner cures and is finish-machined, repeat the same contact stations and compare the pattern with the pre-repair record. Check full-travel handwheel effort, centre height, parallelism, gib adjustment and oil coverage. The objective is not a visually dark mark everywhere; it is stable, appropriate bearing contact with smooth motion and the intended geometry.
Frequently asked questions
Frequently asked questions
Does an uneven contact pattern always mean the liner must be replaced?
No. It can reflect way geometry, gib pressure, contamination, assembly or lubrication. Confirm the cause with repeat measurements before ordering material.
Can spotting paste determine the final liner thickness?
No. It shows contact distribution during a test. Thickness must follow measured geometry, centre height, load and machining allowance.
Should the gib be tightened until the contact looks even?
No. Excessive gib pressure can mask a worn or misaligned way and create tight travel. Set the geometry first, then adjust clearance gradually.