Cutting Speeds. Feeds and Speeds

Transcription

1 CS-1 Feeds and Speeds Production on drills, mills, lathes, grinders, and other machine tools depends on the rate of relative motion between the cutter or grinding wheel and the workpiece. Gears roll together, there is no relative rotation speed difference where teeth mesh. There must be a difference for cutting to take place. The amount of this difference is called SFM or SFPM (Surface Feet Per Minute). When the workpiece or tool, or both, rotate, the difference in speeds at the contacting surface can be calculated from the RPM (Revolutions Per Minute). Because of the many variables in equipment and tool condition, actual speeds may vary. Speeds and Feeds should be as high as practical in order to provide an adequate rate of Production. Practical limits are set by finish requirements, power available, rigidity of the workpiece, the machine tool, and by expected tool life. When the finish is satisfactory, power is sufficient, no present threat of distortion, no burning or breaking, and the tool life is satisfactory, then the speed and feed are not too high. Whenever chatter indicates an incorrect speed or feed, higher as well as lower speeds or feeds should be tried. In feed is the name given to feed that is in the plane of rotation of the cutter or workpiece on mills, lathes, and grinders, into the work. The greater the In Feed, the greater the depth of cut. On drills and surface grinders In Feed is called Down-feed because of it's direction. Cross - Feed is feed perpendicular to the plane of rotation of the workpiece, cutter, or grinding wheel. On a lathe it is set in a number of thousands of an inch per revolution of the workpiece. On surface grinders and mills, it is made by movement of the saddle, perpendicular to the table movement, but in the same X, Y, plane. Cross feed on all machines is mainly limited by tool life and surface finish. Cross feed should be as high as finish requirements and reasonable tool life will allow. The forces at work in machining are by far highest in those interactions due to relative rotation. In feed and cross feed are also factors, but secondary ones. Once appropriate SFPM has been established for the machine tool, and workpiece, correct in feed and cross feed can quickly be made. Turning SFPM The diameter of a round piece of work is the largest measurement perpendicular to the axis across the work. In order to find the distance that passes the tool point in one revolution, the diameter is multiplied by This distance is called the circumference. The diameter is given in inches, therefore the circumference is in inches.

2 (Recommended Surface Feet Per Minute) CS-2 High Speed Steel Carbide -- Tipped Material Rough Finish Rough Finish Coolant Cast Iron Dry Semi-Steel Dry Malleable Iron Soluble, Sulphurized Mineral Oil Cast Steel Soluble, Sulphurized, Mineral or Mineral Lard Oil Copper Soluble, Sulphurized, or Mineral Lard Oil Brass Dry Bronze Soluble, Sulphurized, or Mineral Lard Oil Aluminum Soluble or Sulphurized Oil Mineral Oil and Kerosene Magnesium Dry, Kerosene, or Mineral Lard Oil SAE Steels Soluble, Sulphurized Course Feed Mineral, or Mineral Lard Oil " " Fine Feed " " " " " " Sulphurized and Mineral Oils Stainless Steel " "

3 CS-3

4 CS-4 Definition of Cutting Speed Cutting speed is the rate at which a point on the circumference of a cylindrical workpiece passes a cutting tool. Cutting speeds are given in Feet Per Minute, while spindle speed is given in Revolutions Per Minute, thus the peripheral speed of the workpiece (speed at circumference) must be converted to Revolutions Per Minute (RPM) in order to determine the required spindle speed. The following formula is used; RPM = C.S. x 4 D Legend C.S. = Cutting Speed D = Workpiece or Cutter Dia. Example: Machine a workpiece 3/4" in diameter from Stainless Steel. 1. RPM = C.S. x 4 D 2. R.P.M. = 40 x R.P.M R.P.M. = 213

5 For Various Diameters CS-5 The following chart revolutions are based on the formula; RPM= CS x x D Meters Per Minute Feet Per Minute 50' 60' 70' 80' 90' 100' 110' 120' 130' 140' 150' 200' 300' Diameter mm Inches Revolutions Per Minute 1.6 1/ / / / / / / / / / / / / / / / / / / / /

6 CS-6 Cutting, Rim, and Surface Speed Formula's C.S. = Cutting Speed R.S. = Rim Speed S.S. = Surface Speed = R.P.M. = Revolutions Per Minute D = Diameter of Workpiece or Milling Cutter C.S. = D x RPM RPM = CS x D R.S. = D x RPM RPM = RS x D S.S = D x RPM RPM = SS x D D = C.S. x 12 RPM x

7 (Calculating -- RPM's) CS-7 Calculate the revolutions per minute for the following machining jobs and select an available machine tool RPM from the list. (Please calculate both Rough and Finish Cuts) Machine tool revolutions per minute available; Tool Work Work Recommended RPM Material Material Dia. SFPM From above list Carbide Cast Iron 2.00 HSS StainlessSteel HSS Malleable 1/2" Iron Carbide Copper 5/8" Carbide Brass HSS Bronze 7/8" Carbide Aluminum 2.25 HSS Magnesium HSS 1050 c.s Rough Finish Rough Finish

8 CS-7 Q1 Cutting Speed Quiz 1. How many RPM's are required to turn a gear blank 4.5" in diameter at a cutting speed of 42 FPM? 2. A piece of Tool Steel, 3/4" in diameter is turned in a lathe. How many RPM's are necessary if the cutting speed is 30 FPM? 3. If turning a Cast Iron Pulley, 14" in diameter. what RPM's are necessary using a cutting speed of 46 FPM? 4. It is desired to turn a 3/8" diameter screw at 70 FPM. Then a thread is to be chased at 20 FPM. Find the turning RPM and the threading RPM. 6. Find the Revolutions Per Minute for the following; (A) Drill a 3/16" diameter hole in brass. (B) Bore a 2 1/4" hole in aluminum. (C) Mill the surface of low carbon steel with a 3/4" end mill. (D) Turn a 2" diameter workpiece made from cast iron material. (E) Chase a 1/2-13 thread on stainless steel using a single point threading tool.