Cutting Speeds and Spindle RPM for Drilling Various Materials


 
 
Spindle RPM for Drill Size
Material
SFPM
1/4"
1/2"
3/4"
1"
2"
3"
4"
5"
6"
Tool Steel
30
450
220
150
110
60
40
30
45
20
Stainless
30
450
220
150
110
60
40
30
45
20
Cast Steel
35
530
260
180
130
70
45
33
27
22
Cast Iron
50
760
380
250
190
95
64
48
38
32
Carbon Steel
60
910
450
300
230
115
76
57
46
38
Mild Steel
70
1000
530
350
260
130
90
67
53
44
Bronze
100
1500
760
500
380
190
130
95
76
64
Brass
200
3000
1500
1000
760
380
250
190
150
130
Aluminum
300
4560
2280
1500
1140
570
380
280
220
190
Plastic
1000
15000
7600 
5000 
3800 
1900 
1200 
950  
760  
640  

Speeds are in Surface Feet per Minute, are specified for High-Speed Steel drill bits, and are approximate for normal drilling operations.

Speeds should be halved when using Carbon Steel bits, and can be doubled for Carbide bits. Use coolant judiciously.

For Milling operations speeds may be increased by 50%. Lathe turning speeds may be increased by 100%.

The best rule of thumb for proper cutting speed is the color of the chip (when cutting steels). Using a high-speed steel drill bit the chips should never be turning brown or blue. Straw colored chips indicate that you are on the maximum edge of the cutting speed for your cutting conditions. When using Carbide bits, chip colors can range from amber to blue, but never black. A dark purple color will indicate that you are on the maximum edge of your cutting conditions.