Machinery's Handbook, 31st Edition
1092 USING THE SPEEDS AND FEEDS TABLES geometry are illustrated in Fig. 1 and Fig. 2. Many combinations of feed, lead angle, nose radius and cutter diameter, axial and radial depth of cut, and numbers of teeth can give the same value of ECT. However, for a constant cutting speed, no matter how the depth of cut, feed, or lead angle, etc., are varied, if a constant value of ECT is maintained, the tool life will also remain constant. A constant value of ECT means that a constant cutting speed gives a constant tool life and an increase in speed results in a reduced tool life. Likewise, if ECT were increased and cutting speed were held constant, as illustrated in the generalized cutting speed versus ECT graph that follows, tool life would be reduced.
CELe
r
a = depth of cut A = A ' = chip cross-sectional area CEL = CELe = engaged cutting edge length ECT = equivalent chip thickness = A ' /CEL f = feed/rev r = nose radius LA = lead angle (US) LA(ISO) = 90 − LA
A' A
f
LA (ISO)
LA (US)
Fig. 1. Cutting Geometry, Equivalent Chip Thickness, and Cutting Edge Length
CEL
A
A – A
LA (ISO)
Rake Angle
A
LA (US)
Fig. 2. Cutting Geometry for Turning In the tables, the optimum feed/speed data have been calculated by COMP to achieve a fixed tool life based on the maximum ECT that will result in successful cutting, without premature tool wear or early tool failure. The same tool life is used to calculate the average feed/speed data, but these values are based on one-half of the maximum ECT . Because the data are not linear except over a small range of values, both optimum and average sets are required to adjust speeds for feed, lead angle, depth of cut, and other factors.
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