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Unformatted text preview: EML 2322L -- MAE Design and Manufacturing Laboratory Drilling Speeds and Feeds The speed of a drill is usually measured in terms of the rate at which the outside or periphery of the tool moves in relation to the work being drilled. The common term for this is "surface feet per minute", abbreviated as sfm. Every tool manufacturer has a recommended table of sfm values for their tools. General sfm guidelines are commonly found in resources such as the Machinery Handbook (see Table 1 in this document). The peripheral and rotational velocities of the tool are related as shown in the following equation: V = π * D * N (Eq. 1) where V is the recommended peripheral velocity for the tool being used D is the diameter of the tool N is the rotational velocity of the tool Since the peripheral velocity is commonly expressed in units of feet/min and tool diameter is typically measured in units of inches, Equation 1 can be solved for the spindle or tool velocity, N in the following manner: N [rpm] = 12 [in/ft] * V [sfm] / ( π * D [in/rev]) (Eq. 2) Equation 2 will provide a guideline as to the maximum speed when drilling standard materials. The optimum speed for a particular setup is affected by many factors, including the following: • Composition & hardness of material • Depth of hole • Efficiency of cutting fluid • Type, condition and stiffness of drilling machine • Stiffness of workpiece, fixture and tooling (shorter is better) • Quality of holes desired • Life of tool before regrind or replacement Table 2 contains recommended feeds for various drill diameters. For each diameter range there is a corresponding feed range. Use the smaller values for stiffer/harder/stronger materials and the larger values for softer materials. To calculate the feedrate, use the following formula: f = N * f r (Eq. 3) where f = feedrate [in/min] N = spindle speed [rpm] f r = feed per revolution [in/rev] In addition, the following rules of thumb should be observed when applicable: • On most jobs, it is usually better to start with a slower speed and build up to the maximum after trials indicate the job can run faster. • Overloading the drill bit by feeding too quickly in Z will result in an excessive chipload on each drill lip, causing the cutting edges to fracture (chip)....
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- Spring '11
- feed, Milling cutter, peripheral velocity