SPEEDS AND MACHINING POWER Machinery's Handbook, 31st Edition
1143
ESTIMATING SPEEDS AND MACHINING POWER Estimating Planer Cutting Speeds.— Whereas most planers of modern design have a means of indicating the speed at which the table is traveling, or cutting, many older planers do not. The following formulas are useful for planers that do not have a means of indicat- ing the table or cutting speed. It is not practicable to provide a formula for calculating the exact cutting speed at which a planer is operating because the time to stop and start the table when reversing varies greatly. The formulas below will provide a reasonable estimate. V c S c L ≈ and S c V c L --- ≈ where V c = cutting speed; fpm or m/min S c = number of cutting strokes per minute of planer table L = length of table cutting stroke; ft or m Cutting Speed for Planing and Shaping.— The traditional HSS cutting tool speeds in Table 1 through Table 4b and Table 6 through Table 9, pages 1095 through 1107, can be used for planing and shaping. The feed and depth of cut factors in Table 5c should also be used, as explained previously. Very often, other factors relating to the machine or the setup will require a reduction in the cutting speed used on a specific job. Cutting Time for Turning, Boring, and Facing.— The time required to turn a length of metal can be determined by the following formula in which T = time in minutes, L = length of cut in inches (or mm), f = feed in inches per revolution (or mm/min), and N = lathe spin dle speed in revolutions per minute. T fN L = When making job estimates, the time required to load and to unload the workpiece on the machine, and the machine handling time, must be added to the cutting time for each length cut to obtain the floor-to-floor time. Planing Time.— The approximate time required to plane a surface can be determined from the following formula in which T = time in minutes, L = length of stroke in feet (or meter), V c = cutting speed in feet per minute (m/min), V r = return speed in feet per minute (m/min); W = width of surface to be planed in inches (or mm), F = feed in inches (or mm), and 0.025 = approximate reversal time factor per stroke in minutes for most planers: . T F W L V V 1 1 0025 c r # = + + c m ; E Speeds for Metal-Cutting Saws.— The table on page 1144 gives speeds and feeds for solid-tooth, high-speed steel, circular, metal-cutting saws as recommended by Saws International, Inc. (sfpm = surface feet per minute = 3.142 3 blade diameter in inches 3 rpm of saw shaft ÷ 12). Also see page 1245 for bandsaw blade speeds. Speeds for Turning Unusual Materials.— Slate , on account of its peculiarly stratified formation, is rather difficult to turn, but if handled carefully, can be machined in an ordi nary lathe. The cutting speed should be about the same as for cast iron. A sheet of fiber or pressed paper should be interposed between the chuck or steadyrest jaws and the slate, to protect the latter. Slate rolls must not be centered and run on the tailstock. A satisfactory method of supporting a slate roll having journals at the ends is to bore a piece of lignum vitae to receive the turned end of the roll, and center it for the tailstock spindle. Rubber can be turned at a peripheral speed of 200 feet per minute (61 m/min), although it is much easier to grind it with an abrasive wheel that is porous and soft. For cutting a rubber roll in two, the ordinary parting tool should not be used, but a tool shaped like a knife; such a tool severs the rubber without removing any material.
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