Thomas Industrial Library

Indexable Insert Tool Holders. — Indexable insert tool holders are made from a good grade of steel which is heat treated to a hardness of 44 to 48 Rc for most normal applications. Accurate pockets that serve to locate the insert in position and to provide surfaces against which the insert can be clamped are machined in the ends of tool holders. A cemented carbide seat usually is provided, and is held in the bottom of the pocket by a screw or by the clamping pin, if one is used. The seat is necessary to provide a flat bearing surface upon which the insert can rest and, in so doing, it adds materially to the ability of the insert to withstand the cutting load. The seating surface of the holder may provide a positive-, negative-, or a neutral-rake orientation to the insert when it is in position on the holder. Holders, therefore, are classified as positive, negative, or neutral rake.

Four basic methods are used to clamp the insert on the holder: 1) Clamping, usually top clamping; 2) Pin-lock clamping; 3) Multiple clamping using a clamp, usually a top clamp, and a pin lock; and 4) Clamping the insert with a machine screw.

All top clamps are actuated by a screw that forces the clamp directly against the insert. When required, a cemented-carbide, plate-type chipbreaker is placed between the clamp and the insert. Pin-lock clamps require an insert having a hole: the pin acts against the walls of the hole to clamp the insert firmly against the seating surfaces of the holder. Multiple or combination clamping, simultaneously using both a pin-lock and a top clamp, is recommended when taking heavier or interrupted cuts. Holders are available on which all the above-mentioned methods of clamping may be used. Other holders are made with only a pocket. Most standard indexable insert holders are either straight-shank or offset-shank, although special holders are made having a wide variety of configurations.

The common shank sizes of indexable insert tool holders are shown in Table 1 . Not all styles are available in every shank size. Positive- and negative-rake tools are also not available in every style or shank size. Some manufacturers provide additional shank sizes for certain tool holder styles. For more complete details the manufacturers' catalogs must be consulted.

Identification System for Indexable Insert Holders.— The following identification system conforms to the American National Standard, ANSI B212.5-2002, Metric Holders for Indexable Inserts.

Each position in the system designates a feature of the holder in the following sequence:

1) Method of Holding Horizontally Mounted Insert: The method of holding or clamping is designated by a letter: C, top clamping, insert without hole; M, top and hole clamping, insert with hole; P, hole clamping, insert with hole; S, screw clamping through hole, insert with hole; W, wedge clamping.

2) Insert Shape: The insert shape is identified by a letter: H, hexagonal; O, octagonal; P, pentagonal; S, square; T, triangular; C, rhombic, 80 ° included angle; D, rhombic, 55 ° included angle; E, rhombic, 75 ° included angle; M, rhombic, 86 ° included angle; V, rhombic, 35 ° included angle; W, hexagonal, 80 ° included angle; L, rectangular; A, parallelogram, 85 ° included angle; B, parallelogram, 82 ° included angle; K, parallelogram, 55 ° included angle; R, round. The included angle is always the smaller angle.

3) Holder Style: The holder style designates the shank style and the side cutting edge angle, or end cutting edge angle, or the purpose for which the holder is used. It is designated by a letter: A, for straight shank with 0 ° side cutting edge angle; B, straight shank with 15 ° side cutting edge angle; C, straight-shank end cutting tool with 0 ° end cutting edge angle; D, straight shank with 45 ° side cutting edge angle; E, straight shank with 30 ° side cutting edge angle; F, offset shank with 0 ° end cutting edge angle; G, offset shank with 0 ° side cutting edge angle; J, offset shank with negative 3 ° side cutting edge angle; K, offset shank with 15 ° end cutting edge angle; L, offset shank with negative 5 ° side cutting edge angle and 5 ° end cutting edge angle; M, straight shank with 40 ° side cutting edge angle; N, straight shank with 27 ° side cutting edge angle; R, offset shank with 15 ° side cutting edge angle; S, offset shank with 45 ° side cutting edge angle; T, offset shank with 30 ° side cutting edge angle; U, offset shank with negative 3 ° end cutting edge angle; V, straight shank with 171 ⁄ 2 ° side cutting edge angle; W, offset shank with 30 ° end cutting edge angle; Y, offset shank with 5 ° end cutting edge angle.

4) Normal Clearances: The normal clearances of inserts are identified by letters: A, 3 ° ; B, 5 ° ; C, 7 ° ; D, 15 ° ; E, 20 ° ; F, 25 ° ; G, 30 ° ; N, 0 ° ; P, 11 ° .

5) Hand of tool: The hand of the tool is designated by a letter: R for right-hand; L, lefthand; and N, neutral, or either hand.

6) Tool Height for Rectangular Shank Cross Sections: The tool height for tool holders with a rectangular shank cross section and the height of cutting edge equal to shank height is given as a two-digit number representing this value in millimeters. For example, a height of 32 mm would be encoded as 32; 8 mm would be encoded as 08, where the one-digit value is preceded by a zero.

7) Tool Width for Rectangular Shank Cross Sections: The tool width for tool holders with a rectangular shank cross section is given as a two-digit number representing this value in millimeters. For example, a width of 25 mm would be encoded as 25; 8 mm would be encoded as 08, where the one-digit value is preceded by a zero.

8) Tool Length: The tool length is designated by a letter: A, 32 mm; B, 40 mm; C, 50 mm; D, 60 mm; E, 70 mm; F, 80 mm; G, 90 mm; H, 100 mm; J, 110 mm; K, 125 mm; L, 140 mm; M, 150 mm; N, 160 mm; P, 170 mm; Q, 180 mm; R, 200 mm; S, 250 mm; T, 300 mm; U, 350 mm; V, 400 mm; W, 450 mm; X, special length to be specified; Y, 500 mm.

9) Indexable Insert Size: The size of indexable inserts is encoded as follows: For insert shapes C , D , E , H . M , O , P , R , S , T , V , the side length (the diameter for R inserts) in millimeters is used as a two-digit number, with decimals being disregarded. For example, the symbol for a side length of 16.5 mm is 16. For insert shapes A , B , K , L , the length of the main cutting edge or of the longer cutting edge in millimeters is encoded as a two-digit number, disregarding decimals. If the symbol obtained has only one digit, then it should be preceded by a zero. For example, the symbol for a main cutting edge of 19.5 mm is 19; for an edge of 9.5 mm, the symbol is 09.

10) Special Tolerances: Special tolerances are indicated by a letter: Q, back and end qualified tool; F, front and end qualified tool; B, back, front, and end qualified tool. A qualified tool is one that has tolerances of ± 0.08 mm for dimensions F , G , and C . (See Table 2 .)

Selecting Indexable Insert Holders. — A guide for selecting indexable insert holders is provided by Table 3b . Some operations such as deep grooving, cut-off, and threading are not given in this table. However, tool holders designed specifically for these operations are available. The boring operations listed in Table 3b refer primarily to larger holes, into which the holders will fit. Smaller holes are bored using boring bars. An examination of this table shows that several tool-holder styles can be used and frequently are used for each operation. Selection of the best holder for a given job depends largely on the job and there are certain basic facts that should be considered in making the selection.

Rake Angle: A negative-rake insert has twice as many cutting edges available as a comparable positive-rake insert. Sometimes the tool life obtained when using the second face may be less than that obtained on the first face because the tool wear on the cutting edges of the first face may reduce the insert strength. Nevertheless, the advantage of negative-rake inserts and holders is such that they should be considered first in making any choice. Positive-rake holders should be used where lower cutting forces are required, as when machining slender or small-diameter parts, when chatter may occur, and for machining some materials, such as aluminum, copper, and certain grades of stainless steel, when positive-negative rake inserts can sometimes be used to advantage. These inserts are held on negative-rake holders that have their rake surfaces ground or molded to form a positive-rake angle.

Insert Shape: The configuration of the workpiece, the operation to be performed, and the lead angle required often determine the insert shape. When these factors need not be considered, the insert shape should be selected on the basis of insert strength and the maximum number of cutting edges available. Thus, a round insert is the strongest and has a maximum number of available cutting edges. It can be used with heavier feeds while producing a good surface finish. Round inserts are limited by their tendency to cause chatter, which may preclude their use. The square insert is the next most effective shape, providing good corner strength and more cutting edges than all other inserts except the round insert. The only limitation of this insert shape is that it must be used with a lead angle. Therefore, the square insert cannot be used for turning square shoulders or for back-facing. Triangle inserts are the most versatile and can be used to perform more operations than any other insert shape. The 80-degree diamond insert is designed primarily for heavy turning and facing operations, using the 100-degree corners, and for turning and back-facing square shoulders using the 80-degree corners. The 55- and 35-degree diamond inserts are intended primarily for tracing.

Lead Angle: Tool holders should be selected to provide the largest possible lead angle, although limitations are sometimes imposed by the nature of the job. For example, when tuning and back-facing a shoulder, a negative lead angle must be used. Slender or smalldiameter parts may deflect, causing difficulties in holding size, or chatter when the lead angle is too large.

End Cutting Edge Angle: When tracing or contour turning, the plunge angle is determined by the end cutting edge angle. A 2-deg minimum clearance angle should be provided between the workpiece surface and the end cutting edge of the insert. Table 3a provides the maximum plunge angle for holders commonly used to plunge when tracing where insert shape identifiers are S = square, T = triangle, D = 55-deg diamond, V = 35-deg diamond. When severe cratering cannot be avoided, an insert having a small, end cutting edge angle is desirable to delay the crater breakthrough behind the nose. For very heavy cuts a small, end cutting edge angle will strengthen the corner of the tool. Tool holders for numerical control machines are discussed in the NC section, beginning page 1309 .