Machinery's Handbook, 31st Edition
1234 SCREW MACHINES SCREW MACHINES, BAND SAWS, CUTTING FLUIDS Automatic Screw Machine Tool Operations Speeds and Feeds for Automatic Screw Machine Tools.— Approximate speeds and feeds for standard screw machine tools are given in Table 1 on page 1235. Knurling in Automatic Screw Machines.— When knurling is done from the cross slide, it is good practice to feed the knurl gradually to the center of the work, starting to feed when the knurl touches the work and then passing off the center of the work with a quick rise of the cam. The knurl should also dwell for a certain number of revolutions, depending on the pitch of the knurl and the kind of material being knurled. See also KNURLS AND KNURLING starting on page 1056. When two knurls are employed for spiral and diamond knurling from the turret, the knurls can be operated at a higher rate of feed for producing a spiral than they can for pro ducing a diamond pattern. The reason for this is that in the first case the knurls work in the same groove, whereas in the latter case they work independently of each other. Revolutions Required for Top Knurling.— The depth of the teeth and the feed per revo lution govern the number of revolutions required for top knurling from the cross slide. If R is the radius of the stock, d is the depth of the teeth, c is the distance the knurl travels from the point of contact to the center of the work at the feed required for knurling, and r is the radius of the knurl. Inch or metric unts may be used in the following equation. c R r R r d 2 2 = + − + − ^ h ^ h Example: If the stock radius R is 5 ∕ 32 inch (or mm), depth of teeth d is 0.0156 inch (or mm), and radius of knurl r is 0.3125 inch (or mm), then . . . . . . c 0 1562 0 3125 0 1562 0 3125 0 0156 0120 inch (or mm) cam rise required 2 2 = + − + − = = ^ h ^ h Example: Assume that it is required to find the number of revolutions to knurl a piece of brass 5 ∕ 16 inch in diameter using a 32 pitch knurl. The included angle of the teeth for brass is 90 degrees, the circular pitch is 0.03125 inch, and the calculated tooth depth is 0.0156 inch. The distance c (as determined in the previous example) is 0.120 inch. Referring to Table 1 on page 1235, the feed for top knurling brass is 0.005 inch per revolution. The number of revolutions required for knurling is, therefore, 0.120 ÷ 0.005 = 24 revolutions. If conditions permit, the higher feed of 0.008 inch per revolution given in the table may be used, and 15 revolutions are then required for knurling. Cams for Threading.— Table 2 on page 1237 gives the revolutions required for thread- ing various lengths and pitches and the corresponding rise for the cam lobe. To illustrate the use of this table, suppose a set of cams is required for threading a screw to the length of 3 ∕ 8 inch in a Brown & Sharpe machine. Assume that the spindle speed is 2400 revolu- tions per minute; the number of revolutions to complete one piece, 400; time required to make one piece, 10 seconds; pitch of the thread, 1 ∕ 32 inch or 32 threads per inch. By refer- ring to Table 2, under 32 threads per inch, and opposite 3 ∕ 8 inch (length of threaded part), the number of revolutions required is found to be 15 and the rise required for the cam, 0.413 inch.
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