Twist Drill Bit

Terminology for multi-facet grinds

General Guidelines for 4-Facet Grind
Drill Bit SIze Point Angle Clearance Angle Notes & Recommended Tormek Jig
Inch
Decimal
Inch
Fraction
Metric (mm) Wire Number Letter Mild Metal, Wood Hard Steel
< 0.125 < 1/8 < 3.0 > 31 118° 14° 11° Can't use the Tormek DBS-22 Drill Bit Sharpening Attachment with these bits -- they are too small. (See also Note 1, below)
0.125 - 0.250 1/8 - 1/4 3.0 - 6.0 31 - 1 A - E 118°
14°
11°
Bits as small as 1/8 inch can be held in the Tormek DBS-22, but they can flex easily. A pin vice can assist with reducing this flex.

Tormek DBS-22
0.250 - 0.500 1/4 - 1/2 6.5 - 12.0 F - Z 118°
11°

0.500 - 0.875 1/2 - 7/8 12.5 - 22.0 118°


> 0.875 > 7/8 > 22.0


Can't use the Tormek DBS-22 Drill Bit Sharpening Attachment with these bits -- they are too large

Notes:

  1. One sharpener has used a precision pen vice (like the Starrett 166C ) with the Tormek DBS-22 to hold bits as small as wire number 61 (= 0.0390" ≈ 5/128" ≈ 1 mm).

Material-Based Guidelines
Material Type Point Angle Clearance Angle Notes
Recom. Range Recom. Range
Aluminium 118°
90 - 130°
(as above)
12 - 15°
Clearance angles based on drill bit size should be used.
Armour Plate 135°
135 - 140°

6 - 9°
Brass 118°
118°
(as above)
12 - 15°
Clearance angles based on drill bit size should be used.
Bronze 118°
110 - 118°
(as above)
12 - 15°
Clearance angles based on drill bit size should be used.
Bronze, High Tensile 105°
100 - 110°
(as above)
12 - 15°
Clearance angles based on drill bit size should be used.
Cast Iron, Soft 95°
90 - 100°
(as above)
12 - 15°
Clearance angles based on drill bit size should be used.
Cast Iron, Medium 105°
100 - 110°
(as above)
12 - 15°
Clearance angles based on drill bit size should be used.
Cast Iron, Hard 110°
100 - 118°

8 - 12°
Cast Iron, Chilled 118°
118 - 135°

5 - 9°
Copper 118°
100 - 118°
14°
12 - 15°
Iron, Malleable 95°
90 - 100°
14°
12 - 15°
Magnesium and Alloys 95°
70 - 118°
14°
12 - 15°
Monel Nickel 120°
118 - 125°
11°
10 - 12°
Nickel Alloys 135°
135 - 140°

5 - 7°
Plastic, Hot Set 90°
60 - 90°
11°
10 - 12°
Minimum point angle on the Tormek DBS-22 Drill Bit Sharpening Attachment is 90°.
Plastic, Cold Set 125°
118 - 135°
14°
12 - 20°
Steel, Low Carbon 118°
110 - 118°

7 - 9°
Steel, Medium Carbon 118°
118 - 125°

7 - 9°
Steel, High Carbon 130°
118 - 145°

7 - 9°
Steel, Forged 130°
118 - 145°
11°
7 - 12°
Steel, Alloy 118°
118 - 125°
11°
10 - 12°
Steel, Stainless 115°
110 - 118°
11°
8 - 12°
Steel, Stainless, Hard 125°
118 - 135°

6 - 8°
Steel, Manganese 145°
140 - 150°

7 - 10°

Notes & Comments

Information regarding Grindstones

If you pursue sharpening small bits (< 1/8 in / < 3.0 mm),


For tougher materials, a secondary point angle (SPA) is useful for reducing the stress on the outside cutting lip corners. (This is well outlined in Joseph Mazoff's document {see below}.) However, the Tormek DBS-22 Drill Bit Sharpening Attachment is not designed for a grinding SPAs, so it is not outlined here.


The Tormek DBS-22 Drill Bit Sharpening Attachment is not designed for a 6-facet grind, so values are not shown for it. A modification to the DBS-22 was made by Janne for 6-facet grinding, and more information can be found on the Tormek Forum.


More Information

Books & Papers

Videos & Presentations

Web Sites


Tormek is a copyrighted logo of Tormek AB. Its presentation on this site is used to help the user quickly understand when specific Tormek tools, jigs, or setting are being used. For specific information regarding Tormek AB, or its products, please refer to the www.Tormek.com. Some information presented is from Tormek's handbook, Water Cooled Sharpening of Edge Tools.


About this site
Remember : The goal of sharpening is to produce sharp tools, and these tools can injure you if mishandled. Safety measures should be followed to protect yourself and those in your shop. Be sure to read and follow all instructions from the manufacturer, and and utilize proper safety equipment. Never consume alcohol or anything that could impair your judgement before sharpening tools, or using sharp tools. Comments can be sent via eMail to me at SharpeningHandbook@Gmail.com.