Machinery's Handbook, 31st Edition
1084
SPEEDS AND FEEDS Table 1. Tool Troubleshooting Check List Table 1. (Continued) Tool Troubleshooting Check List
Tool Material
Problem
Remedy
Poor surface finish (Continued)
HSS
1. Use a high additive EP cutting fluid 2. Increase the nose radius 3. Reduce the feed
4. Increase the relief angles 5. Increase the rake angles
1. Use diamond tool for soft materials
Diamond
Notching at the depth of cut line
Carbide and HSS 1. Increase the lead angle 2. Reduce the feed Cutting Speed Formulas
Most machining operations are conducted on machine tools having a rotating spindle. Cutting speeds are usually given in feet or meters per minute and these speeds must be converted to spindle speeds, in revolutions per minute, to operate the machine. Conver- sion is accomplished by use of the following formulas: US Units: N D V 12 8 12 252 120 rpm # # π π = = = Metric Units: . N D V D V 1000 318 3 rpm = π = where N is the spindle speed in revolutions per minute (rpm); V is the cutting speed in feet per minute (fpm) for US units and meters per minute (m/min) for metric units. In turning, D is the diameter of the workpiece; in milling, drilling, reaming, and other operations that use a rotating tool, D is the cutter diameter in inches for US units and in millimeters for metric units. π = 3.1416. Example: The cutting speed for turning a 4-inch (101.6-mm) diameter bar has been found to be 575 fpm (175.3 m/min). Using both the inch and metric formulas, calculate the lathe spindle speed. US Units: Metric Units: . . . . N D V N D V 12 31416 4 12 575 549 1000 31416 1016 1000 175 3 549 rpm rpm × × × × π π = = = = = = When the cutting tool or workpiece diameter and the spindle speed in rpm are known, it is often necessary to calculate the cutting speed in feet or meters per minute. In this event, the following formulas are used. US Units: V DN 12 fpm = π Metric Units: V DN 1000 m/min = π As in the previous formulas, N is the rpm and D is the diameter in inches for the US Units formula and in millimeters for the metric formula. Example: Calculate the cutting speed in feet per minute and in meters per minute if the spindle speed of a 3 ⁄ 4 -inch (19.05-mm) drill is 400 rpm. US Units: . . . . V DN V DN 12 12 075 400 785 1000 19 05 400 24 9 fpm m/min × × × × π π π π = = = = = = Metric Units: 1000
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