Sharpening Handbook

Twist Drill Bit

Terminology for multi-facet grinds

General Guidelines for 4-Facet Grind
Drill Bit SIze					Point Angle	Clearance Angle		Notes
Inch Decimal	Inch Fraction	Metric (mm)	Wire Number	Letter	Point Angle	Mild Metal, Wood	Hard Steel	Notes
< 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. However, one sharpener has used a precision pen vice (like the Starrett 166C ) with the Tormek DBS-22 to hold bits as small as #61 (⁵/₁₂₈ in. / 1 mm).
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.
0.250 - 0.500	¹/₄ - ¹/₂	6.5 - 12.0		F - Z	118°	11°	9°
0.500 - 0.875	¹/₂ - ⁷/₈	12.5 - 22.0			118°	9°	7°
> 0.875	> ⁷/₈	> 22.0						Can't use the Tormek DBS-22 Drill Bit Sharpening Attachment with these bits -- they are too large

Material-Based Guidelines
Material Type	Point Angle		Clearance Angle		Notes
Material Type	Recom.	Range	Recom.	Range	Notes
Aluminium	118°	90 - 130°	(as above)	12 - 15°	Clearance angles based on drill bit size should be used.
Armour Plate	135°	135 - 140°	7°	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°	9°	8 - 12°
Cast Iron, Chilled	118°	118 - 135°	7°	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°	7°	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°	9°	7 - 9°
Steel, Medium Carbon	118°	118 - 125°	9°	7 - 9°
Steel, High Carbon	130°	118 - 145°	9°	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°	7°	6 - 8°
Steel, Manganese	145°	140 - 150°	9°	7 - 10°

Notes & Comments

Information regarding Grindstones

Drill Bit Sizes (Metric, Fractional, Letter, & Number)
Tap & Clearance Drill Sizes (Metric & Fractional)

The document, Drill Bit Geometry, by Joseph Mazoff is a truly great reference about drill bit geometry.

Another great general reference is the U.S. War Department's TM 9-867 Maintenance and Care of Hand Tools.

If you pursue sharpening small bits (< ¹/₈ in / < 3.0 mm),
1. A pin vice like the Starrett 166C is recommended. Having the pin vice's handle being larger than the knurled area allows the Tormek DBS-22 to hold the pin vice without it shifting. (Yes, that is something I learned the hard way.)
2. You will need a good magnifying glass and good light. These are difficult to see with the naked eye (especially in poor light).
3. Care must be taken when grinding the secondary facet on bits this small. It is very easy to over grind this. Check after each pass on the grindstone.
4. Consider honing the primary grind with a high grit stone (e.g., Tormek SJ-250 Japanese Waterstone). There is no need to hone the secondary facet as it is merely to allow space for chip evacuation.

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.) 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.

Some information presented is from Tormek handbook, Water Cooled Sharpening of Edge Tools, © Tormek AB. The User Manual for the DBS-22 Drill Bit Jig is quite useful.

Good videos showing the use of the Tormek DBS-22 Drill Bit Sharpening Attachment:

Tormek Live Sharpening Class - Part 6 - Drill bit sharpening

It's time for drill bit sharpening! Learn how to sharpen your drill bits with maximum precision, to the greatest sharpness. We will show you how to create a 4-facet point which gives the ideal cutting performance.

Sharpen drill bits with Tormek Drill Bit Sharpening Attachment

Tormek DBS-22

Tormek Drill Bit Sharpening Attachment

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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.