TABLE OF CONTENTS | Work Material | Point Angle | Comments |
|---|---|---|
| General work | 118 | Lip relief angle [a] 10 15 Helix angle 24 32 |
| High strength (tough) steels | 118 135 | Lip relief angle [a] 7 12 Helix angle 24 32 |
| Aluminum alloys, cast iron | 90 140 | Lip relief angle [a] 10 15 |
| Magnesium and copper alloys | 70 118 | Lip relief angle [a] 10 15 Helix angle 10 30 |
| Deep holes (various materials) or drilling stainless steel, titanium alloys, high temperature alloys, nickel alloys, very high strength materials, tool steels | 118 Split point or crankshaft drill point. | Lip relief angle 9 Chisel edge is entirely eliminated |
| Note: Improperly sharpened twist drills, that is, those with unequal edge length or asymmetrical point angle, will tend to produce holes with poor diameter and directional control. | ||
| [a]The lower values of these angle ranges are used for drills of larger diameter, the higher values for the smaller diameters. For drills of diameter less than 1/4-in, the lip relief angle are increased beyond the listed maximum value up to 24 . For soft and free machining materials, 12 to 18 except for diameters less than 1/4 inch, 20 to 26 . |
| Fraction No. or Letter | mm | Equivalent | Fraction No. or Letter | mm | Equivalent | ||
|---|---|---|---|---|---|---|---|
| Inch | mm | Inch | mm | ||||
| 80 | 0.0135 | 0.343 | 57 | 0.0430 | 1.092 | ||
| 0.35 | 0.0138 | 0.350 | 1.10 | 0.0433 | 1.100 | ||
| 79 | 0.0145 |
