ASME B94.4-1976 — Identification System for Indexable Inserts for Cutting Tools

🔷 ANSI/ASME B94.4-1976 is the American National Standard defining the identification system for indexable inserts used in both single-point cutting tools and multi-point cutting tools such as milling cutters. Originating from the Standards Committee of the Cemented Carbide Producers Association (approved 1965, reaffirmed 1972), the 1976 edition was revised by Technical Committee 1 (Carbide and Oxide Tools) of the ASME B94 Standards Committee to align as closely as possible with the ISO document on the same subject, maximizing uniformity between the U.S. standard and its ISO counterpart. The Standard defines an identification sequence of up to ten positions, each describing one characteristic of the insert—the de facto “identity card” used in insert selection, procurement, stock control, and tool programming.

1. Scope and Identification Sequence 📌

This Standard covers the identification system for indexable type inserts for both single point cutting tools and multi-point cutting tools such as milling cutters. It includes items now commonly used and facilitates identification of items not in common use. Identification consists of up to ten positions, each defining a characteristic in the following order:

1. Shape
2. Clearances (relief angles)
3. Tolerance class
4. Type (if needed)
5. Size
6. Thickness
7. Cutting point configuration
8. Special cutting point definition
9. Other conditions
10. Hand

2. Shape and Clearance Coding 🔤

Position 1 (Shape) uses a letter symbol, descriptive of the shape wherever possible:

Position 2 (Clearances) is a letter denoting the relief angles—the complement of the included angle between flank and top, measured in a plane normal to the cutting edge. Common codes: N=0°, A=3°, B=5°, C=7°, P=11°, D=15°, E=20°, F=25°, G=30°. Dual-value codes (H=0°–11°, J=0°–14°, K=0°–17°, L=0°–20°, M=11°–14°, R=11°–17°, S=11°–20°) state the primary cutting-edge relief first and the faceted-edge relief second; the secondary facet angle may vary by ±1°.

3. Tolerance Class, Type, Size, and Thickness 📏

Position 3 (Tolerance class) is an arbitrary letter indicating the tolerances that control the indexability of the insert; the specified tolerances do not imply the method of manufacture. The Standard tabulates tolerance combinations on the inscribed circle (I.C.) dimension A, the edge dimension B, and thickness T for classes such as A through N and U. For example, tight classes hold the I.C. to ±0.0002 in. with thickness ±0.001 in., while class U is generous (0.005–0.012 in.), typically for inserts where precise indexing is not critical. Values depend on whether the insert has facets (secondary cutting edges), a fixing hole, or chip grooves; some tolerances follow the corresponding shapes and sizes per ASME B94.25.

Position 4 (Type), used only when needed, describes construction features—for example, cylindrical fixing hole with two counter-sinks and chip grooves on both rake faces, hole with one chip groove, or smaller-than-1/4-in.-I.C. configurations. Positions 5 and 6 state size (e.g., inscribed-circle series in 1/16-in. steps) and thickness (in 1/16- or 1/32-in. steps).

4. Cutting Point, Special Edge, and Hand 🔪

Position 7 (Cutting point configuration) defines the edge form—for example, chip grooves, chamfer, or negative land geometry. Position 8 (Special cutting point definition) adds detail for special edge forms (land width and angle). Position 9 (Other conditions) covers any remaining features, and Position 10 (Hand) indicates right- or left-hand inserts where applicable. Appendix A provides an identification chart for quick decoding and Appendix B a conversion chart from inch to millimeter for metric users.

5. Engineering Practice Essentials 🛠️

• 🔍 Decoding workflow: for a code like TCMT-110304, read position by position—shape (T=triangle), clearance (C=7°), tolerance (M), type (T=with hole), size, thickness, and nose radius (04 = 0.4 mm)—then verify against the maker’s catalog.
• 🔧 ISO alignment: since B94.4 closely parallels the ISO insert document, give both formats (e.g., ISO 1832) on purchase orders to guarantee compatibility of inserts, holders, and seats across borders.
• 📊 Indexing management: schedule index cycles from the number of cutting edges; clean the pocket and seating surfaces before each index to preserve repeatability; replace worn edges promptly.
• 📋 Stock and error-proofing: archive stock by the full ten-position code; use color labels or barcodes in the tool crib to avoid mixing similar diamond families (C/D/E/V) and wrong assembly.

6. Frequently Asked Questions ❓