News
Indexable cutting tools have replaced solid-ground tooling across most production shops because they allow a worn cutting edge to be rotated or replaced without removing the tool body from the machine. A full inserts series typically covers turning, milling, drilling, and grooving geometries, each engineered around a specific chip formation pattern, entry angle, and material removal rate. The economics are straightforward: a single insert body may carry two, four, six, or even eight usable cutting edges, which lowers cost per edge while keeping cycle times predictable.
Shops that standardize on a coherent insert lineup also reduce setup variability. When the geometry, coating, and grade of an insert are matched correctly to the workpiece material, tool life becomes a planning variable rather than a source of downtime. This article walks through insert nomenclature, the three main insert families, a practical selection framework, and tool holder compatibility considerations.
Every indexable insert carries a code string, typically nine positions long, that describes its shape, clearance angle, tolerance class, fixing method, size, thickness, corner geometry, cutting edge condition, and cutting direction. Reading this code correctly is the fastest way to confirm compatibility before ordering replacement stock.
| Position | Describes | Common Codes |
|---|---|---|
| 1 | Insert shape | C, D, S, T, V, W, R |
| 2 | Clearance angle | N (0 deg), P (11 deg), C (7 deg) |
| 3 | Tolerance class | M, G, U |
| 4 | Fixing hole / chip breaker type | N, M, G, W |
| 5-6 | Cutting edge length (mm) | 09, 12, 16, 22 |
| 7-8 | Thickness (mm) | 03, 04, 08 |
| 9-10 | Corner radius (mm) | 02, 04, 08 |
A code such as CNMG120408 therefore describes a rhombic 80 degree insert, 0 degree clearance, M tolerance class, with a molded chip breaker hole, a 12 mm edge length, 4 mm thickness, and a 0.8 mm corner radius. Keeping this decoding chart near the CNC programming station reduces ordering errors and prevents downtime caused by mismatched replacement stock.
Turning inserts are mounted on a single-point tool holder for lathe operations and are selected primarily around three variables: nose angle, chip breaker geometry, and edge preparation. A smaller nose angle such as 55 degrees allows access into tighter contours but carries less edge strength than an 80 or 90 degree rhombic shape.
For stainless and heat resistant alloys, a positive rake edge preparation with a light honed edge reduces cutting forces and built up edge formation. For cast iron and hardened steel finishing, a negative rake with a stronger chamfered edge resists chipping under intermittent contact.
Milling inserts differ from turning inserts because the cutting edge repeatedly enters and exits the workpiece, creating thermal and mechanical shock with every rotation. Square and octagonal shapes offer multiple usable corners per insert, which lowers cost per edge in face milling, while round inserts distribute cutting force evenly and are preferred for contour or plunge milling in tough alloys.
| Insert Shape | Edges per Insert | Best Suited Operation |
|---|---|---|
| Square | 4 (8 with double-sided) | Face milling, shoulder milling |
| Round | Continuous | Contour milling, high feed roughing |
| Triangle | 3 (6 double-sided) | General purpose, medium depth cuts |
| Octagon | 8 | Heavy face milling, cost-per-edge focus |
Positive rake milling inserts cut with lower spindle load, which benefits thin walled parts and machines with limited horsepower. Negative rake, double-sided inserts double the number of usable edges and suit heavier roughing passes where edge count and cost per part matter more than power consumption.
Drilling inserts operate under different mechanics than turning or milling inserts because the outer and inner cutting edges travel at very different surface speeds within the same hole. Indexable drill bodies typically use two insert positions: an outer insert that controls hole diameter and finish, and a central insert that handles the lower speed zone near the drill axis.
Common failure modes in drilling inserts include chip packing in deep holes, off-center wander at entry, and premature outer-corner wear. These are typically addressed through coolant-through drill bodies, a controlled point angle around 130 to 140 degrees for reduced thrust force, and coated grades selected for abrasion resistance in the outer position specifically.
Selecting the correct insert grade and geometry comes down to four variables evaluated together rather than in isolation: workpiece material, machine rigidity, target surface finish, and production volume. Treating any one variable alone often leads to premature edge failure or unnecessary tool cost.
| Material Group | Typical Grade Focus | Recommended Coating |
|---|---|---|
| Carbon and alloy steel | Wear resistant, heat tolerant | Multilayer coated carbide |
| Stainless steel | Toughness with built up edge resistance | PVD coated fine grain carbide |
| Cast iron | Abrasion resistant | CVD coated carbide or ceramic |
| Aluminum and non-ferrous | Sharp, low friction edge | Uncoated polished carbide |
| Hardened steel (45 to 65 HRC) | High hardness, thermal stability | CBN or ceramic tipped |
An insert only performs to its rated capability when clamped in a holder that matches its shape, size, and rigidity requirement. Mismatched holders are a frequent, overlooked cause of chatter and inconsistent tool life.
| Holder Type | Clamping Method | Typical Use |
|---|---|---|
| Lever clamp (C-type) | Top lever pressure on insert pocket | Quick insert changes, general turning |
| Screw-on clamp (S-type) | Direct screw through insert center hole | Small diameter turning tools |
| Top clamp (M-type) | Clamp plate over insert with locating pin | Heavy roughing, high force operations |
| Face mill body | Wedge or screw clamp per pocket | Milling inserts in multi-tooth cutters |
| Indexable drill body | Screw-retained insert seats at tip | Drilling inserts in two-position layout |
Field data collected across general machining operations shows that insert mismatch is one of the largest controllable variables in tool cost per part. The figures below reflect commonly observed ranges rather than any single facility's results.
Typical tool life increase when chip breaker geometry is matched to actual depth of cut and feed, rather than left at a general purpose default
Common cycle time reduction from selecting a larger nose angle or higher edge count insert where part geometry allows it
Reduction in unplanned tool change interruptions after aligning insert grade with correct material group
The diagram below summarizes the decision path from workpiece material to final insert order, condensing the framework covered earlier into a single reference flow.
Rotate the edge as soon as flank wear reaches the process limit, typically visible as a wear land beyond 0.2 to 0.3 mm on steel finishing operations, or sooner if surface finish or dimensional drift is observed before that point.
A general purpose grade can handle both in low volume settings, but dedicated roughing and finishing grades typically outperform a single compromise grade once production volume justifies carrying separate stock.
The most common causes are excessive feed rate relative to the point angle, chip packing from insufficient coolant flow, and outer insert wear that shifts load onto the central insert unevenly.
Not always. A higher edge count insert often carries a smaller edge length and less strength per corner, so it can underperform in heavy roughing even though the nominal cost per edge is lower.
Reduced holder rigidity increases vibration at the cutting edge, which accelerates micro-chipping regardless of how well the insert grade matches the material, making holder selection a genuine part of the tool life equation rather than a separate topic.
ChaiTools is specializing in the research and development, design, production, sales and technical support of high-end CNC tools.
+86-571-83502022
+86-18867120330
+86-18857186736
+86-13615816276
+86-571-82529638
11 Floor of No.2 Wanyushuzhigu Building, Dongrui 4# road, Xintang Street, Xiaoshan District, Hangzhou City, Zhejiang Province, China. POST CODE 311201
Copyright © 2022 Hangzhou Chai Cutting Tools Co., Ltd. All Rights Reserved. CNC Turning Tool Holders Manufacturers
English
Deutsch
русский
Español
中文简体
