Machinery's Handbook, 31st Edition
856 Carbide Tips and Tools Chipbreaker.— The term “chipbreaker” indicates a method of forming or grinding turning tools which will cause the chips to break up into short pieces, thus preventing the formation of long or continuous chips that would occupy considerable space and be difficult to handle. The chipbreaking form of cutting end is especially useful in turning with carbide-tipped steel turning tools because the cutting speeds are high and the chip formation rapid. The chipbreaker consists of a shoulder back of the cutting edge. As the chip encounters this shoulder it is bent and broken repeatedly into small pieces. Some tools have attached or “mechanical” chipbreakers, which serve the same purpose as the shoulder. Chipless Machining.— Chipless machining is the term applied to methods of cold form ing metals to the required finished part shape (or nearly finished shape) without the pro duction of chips (or with a minimum of subsequent machining required). Cold forming of steel has long been performed in such operations as wire-, bar-, and tube-drawing; cold-heading; coining; and conventional stamping and drawing. However, newer meth- ods of plastic deformation with greatly increased degrees of metal displacement have been developed. Among these processes are the rolling of serrations, splines, and gears; power spinning; internal swaging; radial forging; the cold forming of multiple-diameter shafts; cold extrusion; and high-energy-rate forming, which includes explosive forming. The processes of cold heading, thread rolling and rotary swaging are also considered chipless machining processes. Indexable Insert Holders for NC.— Indexable insert holders for numerical control lathes are usually made to more precise standards than ordinary holders. Where appli- cable, reference should be made to American National Standard B212.3-2002, Preci- sion Holders for Indexable Inserts. This standard covers the dimensional specifications, styles, and designations of precision holders for indexable inserts, which are defined as tool holders that locate the gage insert (a combination of shim and insert thicknesses) from the back or front and end surfaces to a specified dimension with a ± 0.003 inch ( ± 0.08 mm) tolerance. In NC programming, the programmed path is that followed by the center of the tool tip, which is the center of the point, or nose radius, of the insert. The surfaces produced are the result of the path of the nose and the major cutting edge, so it is necessary to compensate for the nose or point radius and the lead angle when writ- ing the program. Table 1, from B212.3, gives the compensating dimensions for different holder styles. The reference point is determined by the intersection of extensions from the major and minor cutting edges, which would be the location of the point of a sharp pointed tool. The distances from this point to the nose radius are L 1 and D 1; L 2 and D 2 are the distances from the sharp point to the center of the nose radius. Threading tools have sharp corners and do not require a radius compensation. Other dimensions of importance in programming threading tools are also given in Table 2; the data were developed by Kennametal, Inc. The C and F characters are tool holder dimensions other than the shank size. In all instances, the C dimension is parallel to the length of the shank and the F dimension is par allel to the side dimension; actual dimensions must be obtained from the manufacturer. For all K style holders, the C dimension is the distance from the end of the shank to the tangent point of the nose radius and the end cutting edge of the insert. For all other holders, the C dimension is from the end of the shank to a tangent to the nose radius of the insert. The F dimension on all B, D, E, M, P, and V style holders is measured from the back side of the shank to the tangent point of the nose radius and the side cutting edge of the insert. For all A, F, G, J, K, and L style holders, the F dimension is the distance from the back side of the shank to the tangent of the nose radius of the insert. In all these designs, the nose radius is the standard radius corresponding to those given in the paragraph Cutting Point Configuration on page 841 .
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