1. Cutting Speeds and Feeds
Unit 41

2. Objectives
Calculate the revolutions per minute (r/min) for inch and metric size drills
Select the feed to be used for various operations
Calculate the revolutions per minute for the reaming operation

3. 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

4. Recommended Cutting Speeds
For every job, choose the drill speed that will result in the best production rates!
Portion of Table 41.1 from text
Drill Size Cutting Speeds in Feet per Min or Meters per Min
in mm ft/min 12 m/min 60 ft/min 18 m/min … 1/ 1/ 3/
Steel Casting Tool Steel

5. Economical Drilling Speed Variables
Most important!
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

6. 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

7. 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 revolutions of the drill necessary to attain proper cutting speed for metal being machined.

8. Simplified Formula
Since not all machines can be set to exact calculated speed, pi (µ) 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.

9. 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.

10. 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

11. Drill Feeds General –purpose Work Drill Size Feed per Revolution
Table 41.2  Drill feeds
Drill Size Feed per Revolution
in. mm in mm
1⁄8 and smaller 3 and smaller to to 0.05
1⁄8 to ¼ to to to 0.1
¼ to ½ to to to 0.18
½ to to to to 0.38
1 to 1 ½ to to to 0.63

12. 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

13. 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)

14. Good Cutting Fluid Cool workpiece and tool Reduce friction
Improve cutting action
Protect work against rusting
Provide antiweld properties
Wash away chips