Given the same shape, size and grade, the chipbreaker is often the difference between a clean operation and a broken edge. It is the moulded groove on the rake face that curls and breaks the chip. This page explains how to read it and how to choose.
What the chipbreaker actually does
A chip leaving the cutting edge wants to form a long ribbon. The chipbreaker groove forces it to curl tightly; the tighter the curl, the higher the stress in the chip, and past a certain point it snaps. Whether it snaps depends on three things: the groove shape, the feed, and the depth of cut.
- Feed too low for the groove → the chip does not reach the breaker wall, stays straight, and comes off as a long ribbon. Dangerous and bad for finish.
- Feed too high → the chip is jammed into the groove, forces spike, and the edge breaks.
- Correct → chips break into short “6”, “9” or comma shapes, roughly 10–30 mm long.
So the chipbreaker sets the usable feed window of the insert. Every manufacturer publishes that window per chipbreaker; the per-model pages on this site list the actual feed range for each SKU.
Reading the code
In CNMG 120408-PM, the PM after the dash is the chipbreaker. There is no universal standard, but the convention across most of the ranges we stock is:
- A letter prefix indicating duty or series — for example F finishing, M medium, R roughing.
- A number that usually increases within the series.
The 60 most common geometries in our catalogue, by intended duty:
| 槽型 | Seen on | Duty |
|---|---|---|
| PB1 | 423 insert records | 精加工 – light feed, steel and stainless |
| PC2 | 381 insert records | 中加工 – general steel and stainless |
| KC2 | 350 insert records | 中加工 – cast iron and steel |
| MM4 | 294 insert records | 中加工 – milling, multi-material |
| MC3 | 180 insert records | 中加工 – stainless and superalloys |
| F | 170 insert records | 精加工 – sharp, very low feed |
| MM3 | 160 insert records | 中加工/semi-finish – milling |
| KD5 | 137 insert records | Heavy roughing – cast iron |
| MC4 | 125 insert records | 中加工/rough – stainless and superalloys |
| PA1 | 119 insert records | 精加工 – steel, low feed |
| KC4 | 112 insert records | 粗加工 – cast iron |
| PC4 | 112 insert records | 中加工/rough – steel |
| M | 111 insert records | 中加工 – general purpose |
| PD8 | 110 insert records | 粗加工 – steel, deep cut |
Match the breaker to the feed, not the depth
The most common field error is choosing a roughing chipbreaker because the depth of cut is large, then running it at finishing feed. The result is a long stringy chip, poor surface, and eventual edge breakage. The reverse error — a finishing breaker at roughing feed — snaps the edge immediately.
Practical approach:
- Decide the feed you need from the surface finish requirement and the machine power available.
- Pick the chipbreaker whose published feed window contains that feed.
- Then check the depth-of-cut window also contains your ap.
- If neither fits, change nose radius rather than forcing the feed.
Positive versus negative geometry
This is separate from the chipbreaker, but it is chosen at the same time.
| Negative (e.g. CNMG, SNMG, WNMG) | Positive (e.g. CCMT, DCMT, TCMT) | |
|---|---|---|
| Rake angle | Negative or zero | Positive |
| Edges usable | Both sides (double-sided) | One side only |
| Edge strength | Higher | Lower |
| Cutting force | Higher | Lower |
| Cost per edge | Lower | Higher |
| Use | 粗加工, external turning, rigid setups | Boring, finishing, thin walls, low power |
Rule: if the setup is rigid and you are removing metal, negative is cheaper and stronger. If you are boring, finishing a thin-walled part, or the machine is small, positive reduces force and chatter.
Diagnosing the wrong choice
| What you see | Means | Change to |
|---|---|---|
| Long continuous ribbon chips | Feed too low for the breaker | Sharper/finishing breaker, or raise feed |
| Chip jams, forces spike, edge breaks | Feed too high for the breaker | 粗加工/stronger breaker, or lower feed |
| Chips break but surface finish is poor | Breaker too aggressive | 精加工 breaker, or larger nose radius |
| Edge chipping on entry | Edge too weak for the interruption | Stronger breaker, honed edge, tougher grade |
| Chatter / vibration marks | Cutting force too high | Positive geometry, smaller nose radius, lower ap |
Related
- ISO insert code decoder
- Turning insert selection guide
- Carbide grades explained
- Cutting parameters calculator
Standards and further reading
The material group definitions used throughout this site follow ISO 513. The manufacturer links below are independent technical references.