1. Negative Rake Inserts

1. Shape

There are 16 standard shapes of indexable inserts, and each shape is identified by a capital letter as follows:

A – Parallelogram 85°; B – Parallelogram 82°; C – Diamond 80° (Rhombic);
D – Diamond 55° (Rhombic); E – Diamond 75° (Rhombic); H – Hexagon 120°;
K – Parallelogram 55°; L – Rectangle 90°; M – Diamond 86° (Rhombic);
O – Octagon 135°; P – Pentagon 108°; R – Round;
S – Square 90°; T – Triangle 60°; V – Diamond 35° (Rhombic); W – Trigon 80°.

2. Clearances (relief angles)

Nine relief angle values have been described in ANSI B212.12-1991 standard. These angles are the difference from 90° measured in a plane normal to the cutting edge generated by the angle between the flank and top surface of the insert. Each relief angle is denoted by a capital letter as follows:

A – 3°; B – 5°; C – 7°; D – 15°; E – 20°; F – 25°; G – 30°; N – 0°; and P – 11°.

3. Tolerance class

There are 14 tolerance classes that control the indexability of the inserts. Each class is denoted by a capital letter. Letters for tolerances are A, B, C, D, E, F, G, H, J, K, L, M, U and N.

Tolerances on dimensions (± from nominal) are denoted by letters A, B and T. Dimension A is the nominal inscribed circle (I.C.) of the insert. Dimension T is the thickness of the insert. For pentagon, triangle and trigon shapes, dimension B is the insert height, i.e., the distance between one side and the opposite corner.

For all other polygons, dimension B is the distance, measured along the bisector of the rounded off corner angle and a gage roll of nominal I.C. size tangent to the two sides opposite the corner.

4. Type

The fourth position is a capital letter denoting differences in design of insert, such as the existence of fixing holes, countersinks and special features on rake surfaces. There are 15 standard types in design as follows:

A – With hole, without chip grooves;
B – With hole, without chip grooves, and one countersink (70°-90°);
C – With hole, without chip grooves, and two countersinks (70°-90°);
F – Without hole with chip grooves on two rake faces;
G – With hole and chip grooves on two rake faces;
H – With hole, one countersink (70°-90°) and chip groove on one rake face;
J – With hole, two countersinks (70°-90°) and chip grooves on two rake faces;
M – With hole and chip groove on one rake face;
N – Without hole, without chip grooves;
Q – With hole, without chip grooves, and two countersinks (40°-60°);
R – Without hole with chip groove on one rake face;
T – With hole, one countersink (40°-60°) and chip groove on one rake face;
U – With hole, two countersinks (40°-60°) and chip grooves on two rake faces;
W – With hole, without chip grooves, and one countersink (40°-60°);
X – With dimensions or details requiring detailed explanation, a sketch or additional specifications.