Machinery's Handbook, 31st Edition
Standard Tapers
1013
STANDARD TAPERS Certain types of small tools and machine parts, such as twist drills, end mills, arbors, lathe centers, etc., are provided with taper shanks which fit into spindles or sockets of cor responding taper, providing not only accurate alignment between the tool or other part and its supporting member, but also more or less frictional resistance for driving the tool. There are several standards for “self-holding” tapers, but the American National, the Morse, and the Brown & Sharpe are the standards most widely used by American manufacturers. The name self-holding has been applied to the smaller tapers—like the Morse and the Brown & Sharpe—because, where the angle of the taper is only 2 or 3 degrees, the shank of a tool is so firmly seated in its socket that there is considerable frictional resistance to any force tending to turn or rotate the tool relative to the socket. The term “self-holding” is used to distinguish relatively small tapers from the larger or self-releasing type. A milling machine spindle having a taper of 3 1 ⁄ 2 inches per foot is an example of a self-releasing taper. The included angle in this case is over 16 degrees and the tool or arbor requires a positive locking device to prevent slipping, but the shank may be released or removed more readily than one having a smaller taper of the self-holding type. Tapers for Machine Tool Spindles.— Various standard tapers have been used for the taper holes in the spindles of machine tools, such as drilling machines, lathes, milling machines, or other types requiring a taper hole for receiving either the shank of a cutter, an arbor, a center, or any tool or accessory requiring a tapering seat. The Morse taper represents a generally accepted standard for drilling machines. See more on this subject, page 1024 . The headstock and tailstock spindles of lathes also have the Morse taper in most cases; but the Jarno, the Reed (which is the short Jarno), and the Brown & Sharpe have also been used. Milling machine spindles formerly had Brown & Sharpe tapers in most cases. In 1927, the milling machine manufacturers of the National Machine Tool Builders’ Association adopted a standard taper of 3 1 ⁄ 2 inches per foot. This comparatively steep taper has the advantage of insuring instant release of arbors or adapters. National Machine Tool Builders’Association Tapers Taper Number a Large End Diameter Taper Number a Large End Diameter 30 1 1 ⁄ 4 50 2 3 ⁄ 4 40 1 3 ⁄ 4 60 4 1 ⁄ 4 a Standard taper of 3 1 ⁄ 2 inches per foot The British Standard for milling machine spindles is also 3 1 ⁄ 2 inches taper per foot and includes these large end diameters: 1 3 ⁄ 8 inches, 1 3 ⁄ 4 inches, 2 3 ⁄ 4 inches, and 3 1 ⁄ 4 inches. Morse Taper.— Dimensions relating to Morse standard taper shanks and sockets may be found in an accompanying table. The taper for different numbers of Morse tapers is slightly different, but it is approximately 5 ⁄ 8 inch per foot in most cases. The table gives the actual tapers, accurate to five decimal places. Morse taper shanks are used on a variety of tools, and exclusively on the shanks of twist drills. Dimensions for Morse Stub Taper Shanks are given in Table 1a, and for Morse Standard Taper Shanks in Table 1b. Also see Table 8 and Table 9 on page 1022 . Brown & Sharpe Taper.— This standard taper is used for taper shanks on tools such as end mills and reamers, the taper being approximately 1 ⁄ 2 inch per foot for all sizes except for taper No. 10, where the taper is 0.5161 inch per foot. Brown & Sharpe taper sockets are used for many arbors, collets, and machine tool spindles, especially milling machines and grinding machines. In many cases there are a number of different lengths of sockets corre sponding to the same number of taper; all these tapers, however, are of the same diameter at the small end. See Table 10, page 1023 .
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