An inspection report should not read like a foreign language. This article walks through all 27 items we check — how each is measured, what the numbers mean, and what a failure implies.
1. Static Geometric Accuracy (Items 1–9)
1. Spindle Radial Runout
Method: test bar in the spindle taper, lever indicator at the spindle nose and at 300mm.
Pass: ≤0.005mm near end, ≤0.015mm at 300mm (standard grade).
Failure implies: worn spindle bearings or taper damage — replacement often costs 8–15% of machine value.
2. Spindle Axial Float
Pass: ≤0.008mm. Excess causes chatter on facing.
3. Table Flatness
Method: precision level or straight edge + indicator, along X, Y and diagonals.
Pass: ≤0.02mm over 1000mm.
4. Squareness (table vs spindle, X/Y/Z)
Pass: ≤0.015mm over 300mm travel. Out-of-square parts come out tapered.
5–7. Straightness & Parallelism of X/Y/Z
Sweep the full travel; look for "waves" in the guideway profile.
8. Spindle Axis Parallel to Z
Pass: ≤0.015mm over 300mm.
9. Positioning & Repeatability (laser interferometer)
Pass: ±0.02mm/300mm positioning, ±0.008mm repeatability (standard grade). Poor repeatability usually means lost ballscrew preload — more fixable than poor positioning.
2. Motion & Drivetrain (Items 10–15)
10. Backlash
Measure reversal play with a lever indicator. Pass: ≤0.01mm (pitch error compensation fixes part of it; mechanical wear does not).
11. Ballscrew Condition
Feel and listen across the full stroke: local tightness indicates local wear or contamination.
12. Guideway Condition
Indicator sweep for wear steps; visual check for scoring and rust.
Reading: steps >0.02mm leave visible chatter marks on finish passes.
13. Tool Changer
Run 50 consecutive tool-change cycles; log failures and cycle time drift.
14. ATC Centering
After exchange, the spindle taper should be clean with no holder scoring.
15. 4th Axis / Rotary Table (if fitted)
Indexing accuracy via polygon mirror + autocollimator, or test cutting.
3. Systems & Functions (Items 16–21)
16. CNC Alarm History
An underrated goldmine: repeated overload / following-error alarms = drivetrain trouble.
17. Servo Load Current
Jog every axis and watch the load meter. Abnormally high = guideway drag or excessive preload.
18. Spindle Thermal Drift
2-hour continuous run: bearing zone temperature rise ≤25°C and stabilizing.
19. Hydraulics
Pressure stability, 30-minute hold test, external leaks.
20. Pneumatics
Air tightness, cylinder speed.
21. Coolant & Chip Conveyor
Coolant pump flow, conveyor load.
4. Electrical & Safety (Items 22–27)
- 22. Cabinet condition: dust, corrosion, repair scars (rat's-nest wiring = red flag)
- 23. Contactors & breakers: model consistency, contact erosion
- 24. Encoders & scales: cleanliness and signal stability
- 25. E-stop & guard circuits: trigger each one individually
- 26. Voltage & phase: verify against destination standards before export
- 27. Test cutting: the most convincing item — aluminum test cut + ballbar or typical part measurement
How to Use the Report
Sort failures into three buckets:
- Software-compensable (backlash, some positioning error) — minor bargaining chips
- Mechanically repairable (bearing replacement, way rescraping) — negotiate by repair cost
- Structural (frame distortion, crash history) — walk away
Want a full sample report, or an inspection plan for a machine on your shortlist? Contact us.