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		118º	14º	11º	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	118º	14º	11º	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	118º	11º	9º
0.500 - 0.875	¹/₂ - ⁷/₈	12.5 - 22.0			118º	9º	7º
> 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	118º	90 - 130º	(as above)	12 - 15º	Clearance angles based on drill bit size should be used.
Armour Plate	135º	135 - 140º	7º	6 - 9º
Brass	118º	118º	(as above)	12 - 15º	Clearance angles based on drill bit size should be used.
Bronze	118º	110 - 118º	(as above)	12 - 15º	Clearance angles based on drill bit size should be used.
Bronze, High Tensile	105º	100 - 110º	(as above)	12 - 15º	Clearance angles based on drill bit size should be used.
Cast Iron, Soft	95º	90 - 100º	(as above)	12 - 15º	Clearance angles based on drill bit size should be used.
Cast Iron, Medium	105º	100 - 110º	(as above)	12 - 15º	Clearance angles based on drill bit size should be used.
Cast Iron, Hard	110º	100 - 118º	9º	8 - 12º
Cast Iron, Chilled	118º	118 - 135º	7º	5 - 9º
Copper	118º	100 - 118º	14º	12 - 15º
Iron, Malleable	95º	90 - 100º	14º	12 - 15º
Magnesium and Alloys	95º	70 - 118º	14º	12 - 15º
Monel Nickel	120º	118 - 125º	11º	10 - 12º
Nickel Alloys	135º	135 - 140º	7º	5 - 7º
Plastic, Hot Set	90º	60 - 90º	11º	10 - 12º	Minimum point angle on the Tormek DBS-22 Drill Bit Sharpening Attachment is 90º.
Plastic, Cold Set	125º	118 - 135º	14º	12 - 20º
Steel, Low Carbon	118º	110 - 118º	9º	7 - 9º
Steel, Medium Carbon	118º	118 - 125º	9º	7 - 9º
Steel, High Carbon	130º	118 - 145º	9º	7 - 9º
Steel, Forged	130º	118 - 145º	11º	7 - 12º
Steel, Alloy	118º	118 - 125º	11º	10 - 12º
Steel, Stainless	115º	110 - 118º	11º	8 - 12º
Steel, Stainless, Hard	125º	118 - 135º	7º	6 - 8º
Steel, Manganese	145º	140 - 150º	9º	7 - 10º

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.

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:

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.