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°	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

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).

Notes & Comments

Information regarding Grindstones

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

• 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.)
• You will need a good magnifying glass and good light. These are difficult to see with the naked eye (especially in poor light).
• 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.
• 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 {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

• 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.


• Tormek's "User Manual for the DBS-22 Drill Bit Jig" is quite useful.

Videos & Presentations

• Tormek Live Sharpening Class - Part 6 - Drill bit sharpening (YouTube video). 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 (YouTube video)


• Tormek DBS-22 (YouTube video)


• Tormek Drill Bit Sharpening Attachment (YouTube video)

Web Sites

• Jigs, Fixtures, & Modifications for the Tormek


• Some DBS-22 Drill Bit Sharpener Modifications are outlined.


• Mica Schmid posted a nice USB spacer jig which makes it easer and faster to set the USB relative to the grindstone, and it also helps ensure the stone is consistently flat relative to the USB.

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.