Locate faults by symptom. The three most common problems: chip clogging → tool breakage, axis deviation → scrap holes, poor surface finish → rework. Chip shape tells mechanical condition; chip color tells thermal condition.
| Symptom | Likely Cause | Priority Actions |
|---|---|---|
| Tool breakage — torsion (−45° break) | Chip clogging; coolant interruption; excessive torque | Check chip shape → clear clog → reduce feed 20% → verify coolant delivery |
| Tool breakage — bending (flat break) | Excessive feed; unbalanced forces; misalignment; poor rigidity | Check alignment → verify bushing clearance → inspect guide pads → reduce feed |
| Hole deviation / bending | Spindle-bushing misalignment; guide pad wear; material hardness variation | Realign → check bushing (<0.02mm) → consider workpiece rotation → inspect pad wear |
| Poor surface roughness | Guide pad wear; insufficient coolant; wrong Vc; BUE; wrong coating | Check pads → increase coolant pressure → optimize Vc → change coating |
| Vibration / chatter marks | Support span >40×D; speed in resonance range; worn pads; runout | Add whip guides → adjust Vc ±20% → check pads → use hydraulic holder |
| Unusual noise / squealing | Resonance; chip clogging; drill wobble; bushing clearance | Change speed 15–20% → check evacuation → verify bushing fit |
| Bell-mouth entrance | Bushing wear; misalignment; bushing oversize; entry feed too high | Replace bushing → realign → verify +0.02mm max clearance → reduce entry feed |
| Rapid tool wear | Vc too high; insufficient cooling; wrong coating; work-hardened layer | Reduce Vc 15–20% → verify coolant flow → select right coating |
| Out-of-tolerance bore dia. | Tool wear (undersize); runout (oversize); thermal expansion | Check tool dia → measure runout (<0.003mm) → control coolant <35°C |
| Chip clogging | Poor chip breaking; insufficient coolant flow; worn chip breaker | Adjust feed for tighter curl → check pump/filter → inspect chip breaker |
| Power overload / stall | Excessive feed; dull tool; hard spots; chip clogging | Reduce feed → replace tool → check material hardness → verify evacuation |
| Built-up edge (BUE) | Low Vc; adhesion-prone material (Al, SS, Ti); low lubrication | Increase Vc 15–20% → add EP additives → use PVD-coated or polished tool |
| Rapid guide pad wear | Filtration >30μm; oil viscosity too low; wrong pad grade | Upgrade filtration to ≤20μm → check viscosity → consider PCD-coated pads |
| Wear Pattern | Appearance | Cause | Action |
|---|---|---|---|
| Flank wear (uniform) | Even wear band on relief face | Normal abrasion; end of tool life | Replace or regrind; plan interval |
| Crater wear | Depression on rake face behind edge | Diffusion wear at high temperature | Reduce Vc; use TiAlN/AlTiN coating |
| Notch wear | Localized groove at depth-of-cut line | Work-hardened layer; oxidation | Increase feed slightly; chamfer edge |
| Built-up edge (BUE) | Adhered material on cutting edge | Low Vc; adhesion-prone material | Increase Vc 15–20%; improve EP additives |
| Chipping / fracture | Small fragments broken from edge | Mechanical shock; chip clogging; runout | Check chip packing; reduce feed variation; minimize runout; use negative rake |
| Thermal cracking | Perpendicular cracks on cutting edge | Cyclic thermal stress; intermittent coolant | Stabilize coolant flow; avoid coolant-off retracts |
| Plastic deformation | Edge flattened or rounded | Extreme heat + pressure; Vc too high | Reduce Vc; upgrade to PCBN or AlTiN-coated |
Do NOT rotate while retracting — this can wedge the broken tool deeper.
Capture depth and cutting parameters for root-cause analysis.
Shallow break (<10×D): try an extraction tool. Deep break: EDM to break up the fragment, or scrap the part.
Inspect chip shape at failure, check alignment, review coolant logs — never restart blind.
Keep coolant flowing during retraction to flush chips out of the bore.
Remove accumulated chips from the drill flutes and the bore entry.
Check the breaker groove for wear or damage.
Re-enter at reduced feed and watch chip shape for the first 20 seconds of cut.
Increase feed (better chip breaking) or increase coolant flow.
| Signal | Gradual change | Sudden change |
|---|---|---|
| Spindle load | Progressive tool wear | Chip clogging |
| Coolant pressure | — | DROP = leak / pump failure; RISE = blocked evacuation channel |
| Vibration | Developing chatter | Incipient tool failure |
| Chip shape | C-chips → longer chips = breaker wear | Abrupt change = process event |