Cutting Speeds and Feeds

1. Cutting Speeds and Feeds Unit 41

2. Cutting Speeds and Feeds • Two important factors • Diameter and material of cutting tool • Type of material being cut • Speed of twist drill referred to as cutting speed, surface speed or peripheral speed • Distance point on circumference of drill will travel in 1 min

3. Steel Casting Tool Steel Drill Size Cutting Speeds in Feet per Min or Meters per Min in mm 40 ft/min 12 m/min 60 ft/min 18 m/min … 1/16 2 2445 1910 3665 2865 1/8 3 1220 1275 1835 1910 3/16 4 815 955 1220 1430 Portion of Table 41.1 from text Recommended Cutting Speeds For every job, choose the drill speed that will result in the best production rates!

4. Most important! Economical Drilling Speed Variables • Type and hardness of material • Diameter and material of drill • Depth of hole • Type and condition of drill press • Efficiency of cutting fluid employed • Accuracy and quality of hole required • Rigidity of work setup

5. Revolutions per Minute • Compute correct number of r/min of drill press spindle for given size drill • Type of material to be drilled • Recommended cutting speed of material • Type of material from which drill is made

6. Formula (Inch) where CS = recommended cutting speed in feet per minute for the material being drilled D = diameter of drill being used Revolution per minute = number of revolutionsof the drill necessary to attain proper cutting speed for metal being machined.

7. Simplified Formula • Since not all machines can be set to exact calculated speed, pi () divided into 12 to simplify formula Example: Calculate r/min required to drill a ½ in hole in cast iron (CS 80) with a high-speed steel drill.

8. Formula (Metric) Convert so all units are in mm Example: Calculate r/min required to drill 15 mm hole in tool steel (CS 18) using a high-speed steel drill.

9. Feed • Distance drill advances into work for each revolution • May be expressed in decimals, fractions of an inch, or millimeters • Three factors govern rate of feed • Diameter of drill • Material of workpiece • Condition of drilling machine

10. Drill Size Feed per Revolution in. mm in. mm 1⁄8 and smaller 3 and smaller .001 to .002 0.02 to 0.05 1⁄8 to ¼ 3 to 6 .002 to .004 0.05 to 0.1 ¼ to ½ 6 to 13 .004 to .007 0.1 to 0.18 ½ to 1 13 to 25 .007 to .015 0.18 to 0.38 1 to 1 ½ 25 to 38 .015 to .025 0.38 to 0.63 Table 41.2  Drill feeds Drill Feeds General –purpose Work

11. Drill Feeds • General rule: feed rate increases as drill size increases • Too coarse – chip cutting edges • Too light – chattering noise, dulls cutting edge • Hard steels or alloys use slower feed • Softer metals drilled with faster feed • Blue steel chips indicate too much heat at cutting edge • Dull cutting edge or too high speed

12. Cutting Fluids • Provide both cooling and lubrication • Properties of an effective liquid in dissipating heat • Able to absorb heat rapidly • Have good resistance to evaporation • Have high thermal conductivity Oil: good lubricant, poor coolant Water: best coolant, no lubricating value (promotes rust)

13. Good Cutting Fluid • Cools workpiece and tool • Reduces friction • Improves cutting action • Protects work against rusting • Provides anti-weld properties • Washes away chips