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- Tool wear diagnosis - flank wear, cratering, chipping, built-up edge, thermal cracking and notch wear, with the correction for each
- Thread milling against tapping - how to choose between the two, and why the comparison should be cost per finished part rather than cost per thread
Read the pattern before changing a parameter
Each failure mode points at one cause, and adjusting in the wrong direction makes it worse. A chipping problem is not solved by reducing the feed if the real cause is runout, and built-up edge is not solved by slowing down.
| Pattern | Cause | Correction |
|---|---|---|
| Uniform flank wear | Normal abrasion at slightly high speed | Reduce speed about ten percent |
| Crater on the rake face | Coating lacks hot hardness | Change coating family, or reduce speed |
| Chipping | Brittle edge, high feed, or vibration | Tougher grade, stronger edge prep, check holder runout |
| Built-up edge | Speed too low, edge blunt, adhesion | Increase speed, sharper edge, different coating |
| Thermal cracking | Temperature cycling | Reduce coolant variation or move to dry cutting |
| Notch at the depth line | Same depth of cut every pass | Vary the depth between passes |
Where a worn holder looks like a worn tool
Chipping on one flute and not the others is a statement about runout, not about the tool. When a single flute carries more load it fails first while the others still have life, and replacing the tool changes nothing because the holder is the cause.
Before adjusting parameters for a chipping problem, measure runout at the cutting edge. If it exceeds the tool's specification, the holder, collet or nut is where the fix belongs.
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Tool Wear Diagnosis
Each wear pattern points to a specific cause. Uniform flank wear means speed is slightly high for the coating. Cratering on the rake face means the coating lacks hot...
Read moreThread Milling vs Tapping
Thread milling cuts a thread by helical interpolation with one small cutter, so one tool covers a range of diameters at a given pitch and a broken tool does not scrap the...
Read moreFrequently asked questions
Why did my tool chip instead of wearing out?
Chipping means the edge fractured rather than abraded, which points to a brittle grade, too high a feed for the edge preparation, or vibration. Check holder runout first, because chipping on one flute only is a runout symptom rather than a tool problem.
What causes crater wear?
The coating or grade lacks hot hardness for the temperature generated on the rake face, so material diffuses into the tool. Moving to a coating with greater hot hardness, or reducing speed, addresses it.
Why is my tool worn in one spot only?
Notch wear at the depth-of-cut line, caused by the tool meeting the same boundary on every pass. Varying the axial or radial depth between passes so the notch does not form in the same place is the most effective correction.
Is some tool wear normal?
Yes. A uniform flank wear land developing gradually across the whole edge is the tool being used up as intended. The patterns worth investigating are the localised, sudden or one-sided ones, because those indicate a correctable cause.
How do I choose between two processes for one feature?
Compare cost per finished part rather than cost per operation. Cycle time, tool cost, scrap risk and the value of the part at that stage all enter the calculation, and on an expensive part the risk of a broken tool frequently outweighs a faster cycle.