ASME B94.47M-1980 — Carbide Chip Breakers Used with Indexable Inserts for Clamp Type Holders

28 10 月, 2026
ASME Standards

📐 ASME B94.47M-1980 is the companion standard to B94.46 seats in the B94 series (Cutting Tools, Holders, Drivers, and Bushings). It specifies the dimensional specifications and styles of solid sintered carbide chip breakers used with indexable inserts in clamp type holders. The chip breaker is a key element of chip control: as the chip flows over the insert rake face during turning, it strikes the raised edge of the breaker and is forced to curl and break, preventing long tangles from wrapping around the workpiece and tool. This Standard is the metric revision of B94.47-1973; U.S. customary units are the controlling values.

💡 Chip breaking (chip control) is a central problem in metal cutting: tightly curled “C” or “6” shaped short chips are easy to remove, harmless to the operator, and avoid scratching the finished surface, while continuous long chips wrap around the holder, chip the insert, and can even create a safety hazard. The chip breaker is the standardized component that makes controlled chip breaking possible.

1. Scope, Definitions, and General 📌

Clause 1 (Scope) states that the Standard covers the dimensional specifications and styles of solid sintered carbide chip breakers. Clause 2 definitions:

Carbide: a sintered material of refractory metals, suitable as a chip breaker material;
Chip Breaker: a carbide solid that is mechanically held for use as a chip breaker;
Inscribed Circle (I.C.): a significant number indicating the size of the inscribed circle, for inserts having an inscribed circle such as round, square, triangle, pentagon, diamond, octagon, and hexagon.

Clause 3 states that the standard styles and designations of the chip breakers are shown on pages 3 through 15 of the Standard.

⚠️ The chip breaker must match the insert shape and size, and when combined with the seat (B94.46) must not change the insert seating height. An over-thick breaker or a mislocated edge either prevents the insert from being clamped or diverts the chip stream. Select the insert, seat, and breaker as one system.

2. The Five-Position Identification System 🏷️

The core of the Standard is the five-position identification system for chip breakers, in the following order:

Position	Meaning	Codes
1st	Insert shape	R Round-Round Back / F Round-Flat Back / S Square / T Triangle / C 80° Diamond / D 55° Diamond / V 35° Diamond / K 100° Diamond
2nd	Ref. insert I.C.	Multiples of 1/8 in (3.175 mm)
3rd	Chip breaker thickness	Multiples of 1/32 in (0.79 mm)
4th	Edge type	A Either-hand single edge / B Either-hand double edge / C Single edge left hand / D Single edge right hand
5th	Theoretical chip breaker width	Letters A–U = 0.010–0.390 in (0.25–9.91 mm)

✅ Example: chip breaker R32AA — R = Round-Round Back insert shape; 3 = inscribed circle 3/8 in (9.5 mm); 2 = thickness 1/16 in (1.59 mm); A = either-hand single edge; A = theoretical chip breaker width 0.010 in (0.25 mm).

3. Chip Breaker Styles and Width Series 📏

The Standard provides combinations of breaker thickness, edge type, and theoretical width for each insert shape. The width letters of the 5th position correspond to the following theoretical width series:

Width Letter	Theoretical Width (in / mm)	Width Letter	Theoretical Width (in / mm)
A	0.010 / 0.25	L	0.230 / 5.84
C	0.050 / 1.27	N	0.270 / 6.86
E	0.090 / 2.29	P	0.310 / 7.87
G	0.130 / 3.30	R	0.330 / 8.38
I	0.170 / 4.32	T	0.370 / 9.40
K	0.210 / 5.33	U	0.390 / 9.91

The theoretical width is the difference between the insert I.C. and the chip breaker width (the “B” dimension); the effective chip breaker width may vary with the manufacturer’s pocket style. Width governs the chip curl radius: a smaller width curls the chip tighter and breaks it sooner; a larger width curls it looser, better accommodating a large chip cross-section.

💡 Edge type selection: single edge (C/D) suits stations with a fixed feed direction; double edge (B) curls chips on both sides and can be turned over to double its life; either-hand (A) fits general holders. For left-hand threads or reverse feeding, always select the right-hand type (D).

4. Chip Breaking Mechanism and Material Requirements 🏭

The breaker is mechanically clamped on or above the insert rake face; its edge stands above the rake face forming a step. The chip is bent a second time as it passes the step and, once the strain exceeds the material’s fracture strain, breaks into short chips. Material requirements resemble those of seats:

Hardness: HRA 90 or above, to resist abrasive wear by the chip;
Impact toughness: must survive interrupted-cut impact without cracking;
Edge quality: the edge must be complete and free of notches, or chips will wrap around the flaw and clog;
Mounting rigidity: no looseness after clamping, or vibration will defeat chip breaking.

🚨 When a chip breaker is chipped or loose, chips lose control and can form tangles tens of centimeters long. These tangles scratch the machined surface, wrap the holder, and seriously risk cutting the operator’s hands during removal. Stop the machine and inspect the breaker as soon as chip control is lost.

5. Engineering Practice Essentials 🛠️

🔍 Parameter matching: feed f determines chip thickness — thicker chips break more easily. At small feeds (f<0.1 mm/rev) use a narrow-edge, small-width breaker; for heavy roughing use a wider edge;
🔧 Combined assembly: assemble in the order insert → seat (B94.46) → chip breaker, confirm the three seating heights agree, then tighten the clamp screw;
🔄 Edge management: single-edge breakers can be reversed or turned over when worn; double-edge types are rotated side to side to extend life;
🧼 Cleaning: remove built-up edge from the breaker edge at every insert change to prevent chip-breaking failure;
📋 Cutting fluid: flood the breaking zone to cool the edge, reduce adhesion, and stabilize chip breaking.

6. Frequently Asked Questions ❓

❓ Q: Can a chip breaker and a seat be interchanged?
A: No. The seat (B94.46) supports the insert from below; the chip breaker (B94.47M) controls chips from above. Their shapes are similar but edges and thicknesses differ — mixing them prevents the insert from being clamped or disables chip breaking.

❓ Q: Chips are not breaking and form long curls — what should I do?
A: First check that the breaker edge is intact and installed in the correct direction; then increase the feed (thicker chips break more readily); alternatively switch to a narrower breaker for tighter curling. If still ineffective, verify the cutting speed and insert grade match.

❓ Q: How does the “theoretical width” relate to actual breaking performance?
A: The theoretical width is the nominal difference between the insert I.C. and the breaker width (B dimension); the effective width varies with the manufacturer’s pocket. Small theoretical width → tighter curl → suited to fine finishing; large theoretical width → looser curl → suited to heavy roughing.

🔍 Q: Why does the 1980 edition carry the “M” designation?
A: M indicates a metric revision. B94.47M-1980 revises B94.47-1973, adding metric conversions alongside the controlling U.S. customary units so the Standard aligns with international usage.