04/10/13Milling: Cutting Speeds & RPM Calculations Machine Shop Home Introduction | Safety | Milling Machines | Speeds/Feeds | Cutting Tools | Broaching | Projects | Tests Feed Rate Calculations Speed/Feeds Home There are three factors that make up the cutting conditions; cutting speed, depth of cut, and feed rate. In this information sheet we will concentrate on feed rate factors and calculations. The table feed rate on milling machines is given in terms of inches per minute (IPM). Inches per minute is the rate at which the tool will advance into the work. The feed rate, that can be used, is determined by the speed of the rotation of the cutter (RPM), the number of cutting teeth on the cutter, and by the size of the chip that the cutter can withstand. The chip size is called the feed rate in inches per tooth or chip load (Figure 1). Figure 1 The recommended values for chip load are based on the cutting tool material, the cutting tool size, and the hardness or machinability rating of the workpiece material. The recommended values for feed per tooth (chip load) can be found in charts in the Machinery’s Handbook, your textbook, and charts given to you by your tool salesperson. A typical feed in inches per tooth chart can be found in Table 2. While the recommended feed rates found in these charts represent good fundamental machining practice, they are however only recommended values. Deviations from these recommended values may be necessary due to certain circumstances. Circumstances such as thin or frail part sizes. The feed rate used on small or thin work may need to be reduced. The work holding technique has a great deal to do with the feed rate. Setups, which lack rigidity, may require a slower feed rate. The configuration of the milling machine may also require an adjustment in the feed rate. Feed rates on C-Frame milling machines can be much heavier than those feed rates used on ram type milling machines. When using large carbide face mills, the available horsepower and the rigidity of the machine spindle will always influence the feed rate. Table 2. Recommended Feed in Inches per Tooth for High-Speed Steel Milling Cutters End Mills Material Hardness, Bhn Depth of Cut .250" Depth of Cut .050" Cutter Diameter Cutter Diameter 3/8 3/4 1 and up 1/8 3/8 3/4 1 and up Face Mills and Shell End Mills Plain or Slab Mills Side Mills Form Relieved Cutters Feed per Tooth, Inch its.foxvalleytech.com/machshop3/speedcalc/feedratecalc.htm 1/3 it should be pointed out that these feed rates setting can only be used under ideal circumstances.008 .005 .007 .3% Carbon Content or Less 180 to 220 220 to 300 300 to 400 .012 .010 .005 Ferritic Stainless Steel 135 to 185 .012 .0005 .003 .001 .004 .008 .004 .003 .006 .0005 .004 .008 .010 .005 Zinc Alloys Brasses and Bronzes 100 to 150 150 to 250 .005 .003 .005 Wrought Aluminum Alloy–Hardened .004 .003 .003 .008 .010 .001 .001 .008 .005 .010 .010 .005 .0005 .010 .010 .008 .007 .004 .002 .004 .001 .008 .001 .004 .001 .04/10/13 Milling: Cutting Speeds & RPM Calculations Feed per Tooth.003 .005 .008 .004 .012 .008 .010 .012 .006 .004 .002 .012 .010 .006 .004 .004 .008 .002 .010 .006 .008 .002 .010 .008 .005 .002 .003 .003 .004 .002 .008 .002 .005 .008 .008 .003 .010 .003 .002 .003 .003 .002 .003 .008 .004 .004 .006 .002 .001 .004 .0005 .003 .006 Plastics Feed Rate Calculations-The feed rate in inches per tooth must be converted into feed rate in inches per minute (IPM) before you can make the feed rate setting on the machine.006 .012 .009 .009 .002 .002 .003 .006 .003 .006 .002 .003 All Alloy Steels Having .018 .020 .005 .006 .001 .002 .008 .008 .005 .003 .005 .006 .003 .010 .010 .014 .008 .004 .001 .002 ./min.001 .005 .002 .004 Martensitic Stainless Steel 135 to 185 185 to 225 225 to 300 .002 Tool Steel 200 to 250 250 to 300 .010 .006 .012 .012 .006 . AISI 1010 to 1030 to 150 150 to 200 .003 .3% Carbon Content 180 to 200 220 to 300 300 to 400 .foxvalleytech.003 .012 .012 .012 .001 .004 .005 .008 .008 .006 .006 .008 .005 Cast Aluminum Alloy–Hardened .0005 .004 .010 .005 .005 .012 .001 .010 .003 .001 .008 .008 .003 .008 .014 .004 .010 .004 .002 .002 .010 .008 .002 . You will typically be given a range of chip load factors to use.006 .003 .005 .006 .002 .0005 .004 .003 .002 .006 .020 .002 .003 .020 .008 .003 .001 .004 .008 .008 .008 .006 .008 .001 .010 .005 .004 .003 .001 .005 .006 .014 .010 .003 .003 .005 .008 .003 .004 .004 Austenitic Stainless Steel 135 to 185 185 to 275 .004 .004 .004 AISI B1111.com/machshop3/speedcalc/feedratecalc.004 .008 .004 .012 .002 .004 . A good rule of thumb is to start out at the low range or average feed per tooth factor and increase the feed rate to the capacity of the machine tool.005 Cast Aluminum Alloy–as Cast . It must also be mentioned that using a chip load that is2/3 its.002 .010 . Inch Plain Carbon Steels.008 .001 .001 .003 .014 .010 .006 .002 .008 .htm .002 .003 .003 .008 .006 .003 .004 .006 .012 .002 .003 .0005 .004 .008 .) = RPM x Chip load x # Teeth This simplified version of the feed rate formula is used in most machine shops.005 Plain Carbon Steels.003 . and the desired surface finish.008 .008 .0005 .003 .001 .008 .001 .008 .006 .004 .003 Cast Iron 150 to 180 180 to 220 220 to 300 .012 .003 .003 .004 .020 .005 .003 . AISI 1040 to 1095 120 to 180 180 to 220 220 to 300 .008 .003 .002 .010 .005 Magnesium Alloys .004 .005 .007 .005 .008 .005 Wrought Aluminum Alloy–Cold Drawn .004 . B1112. the setup.004 .003 .006 .004 .012 .003 .0003 .003 .002 .008 .0005 .003 .003 .014 .012 .004 .012 . Again.008 .001 .006 .006 .004 .001 .0005 .001 .003 .010 .004 .003 .003 .008 .002 .008 .004 .008 .003 .006 .006 .003 .010 .004 .004 .0005 .004 .003 .004 .012 .001 . B1113 140 to 180 .012 .005 .007 .003 Free Cutting Brasses and Bronzes 80 to 100 .005 .008 .007 .002 All Alloy Steels Having More Than .008 .006 .003 .006 . The formula for converting feed rate in inches per tooth into inches per minute is as follows: Feed Rate (in.006 .006 .010 .008 .001 .006 .012 .006 .004 .005 .002 .0003 .006 .004 .008 .008 . ) = 320 x 0. RPM = 320 Feed in inches per tooth (chip load) = 0. Some judgment must be made in selecting the feed rate to use.) = RPM x Chip Load (CL) x # Teeth (flutes) Feed (in. A four flute 0.htm 3/3 . Number of teeth (flutes) = 4 Feed (in.250 inch high speed steel (HSS) end milling cutter is to be used on a piece of 8620 alloy steel with a brinnel hardness of 300.12 in. Lets try another examples. What are your surface finish requirements? A larger feed rate will leave a rougher finish. .500 inch high speed steel (HSS) end milling cutter is to be used on a piece of 1018 steel with a brinnel hardness of 200. consider the following conditions. Top its.04/10/13 Milling: Cutting Speeds & RPM Calculations of the machine tool. the machine cannot be set precisely to the calculated feed rate setting.com/machshop3/speedcalc/feedratecalc. It must also be mentioned that using a chip load that is too small will cause excessive tool wear so don’t just set the feed rate low and think this is correct.) feed in inches per tooth factor found in the chart in figure 2. Try to get to the feed rate that is nearest to the calculated amount. / min. Also. Is the setup very rigid? Go slower for setups that lack a great deal of rigidity. / min. but if you can’t.) = 750 x 0. The closest RPM setting to perform this cut is 750 rpm. calculate the feed rate in inches per minute using the average (avg.004 x 4 Feed = 12 in.) = RPM x Chip Load (CL) x # Teeth (flutes) Feed (in. What is your depth of cut? If it is a deep cut. / min. Follow along using the recommended feed rate charts in figure 2. A two flute. the setup. RPM = 750 Feed in inches per tooth (chip load) = 0. / min. / min. Number of teeth (flutes) = 2 Feed (in. Calculate the RPM setting first to perform this cut using the average (avg.foxvalleytech. Look up the feed per tooth in the charts and calculate the feed rate in inches per minute. but this time we must first calculate the RPM. and the desired surface finish.008 avg. Since the available feed rate settings are generally not infinitely variable.004 avg.008 x 2 Feed = 5. Are you using coolant? You may be able to go to the faster of the two settings if you are using coolant. / min.) cutting speed factor found in the chart in figure 2. go to the slower feed setting. Let’s try some feed rate calculations.