Sharpening Handbook

Metal Lathe Tools : Threading Tools

Angles shown are good for hobbyists; grinds for production shops should consult a specialist.

When both a relief and a clearance angle are outlined (e.g., Side Relief and Front Relief), this is done to facilitate easier resharpening.

It is analogous to Secondary Bevels on woodworking chisels.
Resharpening should be done when the wear land reaches 1.5 mm (¹/₁₆ inch) high.

Angles shown are for either Carbide or HSS

Angles shown are the effective angles, not the ground angles. Effective angles are increased or decreased, based on the angle by which the tool is presented against the work. Additionally, the vertical alignment of the tool (vs. the center line of the work) can also change the effective Front Relief Angle.

All angles are given the nomenclature designated by the American Standards Association (ASA).

Carbide vs. HSS
Material	Compressive Strength	Shear Strength	Max Usable Temp. *
Cemented Carbide	Higher	Lower	1,800 °F
HSS	Lower	Higher	950 - 1,100 °F

* Temperature at which the tool material begins to soften appreciably. For HSS, it depends on the level of cobalt in the HSS.

Tool Shape - 60° Threading Tool

Back Rake	Side Cutting Edge Angle	Nose Flat Width	Nose Flat Angle	Relief Angle	Clearance Angle	Comments
8°	30° (both sides)	based on thread pitch	8°	8°	16°
The flattening off of the Nose is to allow for more support under the tip of the grind, helping to prevent shear in carbide insert. The width of that grind should be no wider than allowed for the defined thread. This is not necessary in HSS, but could be a good practice to extend tool life as dulling will happen later.

Notes & Comments

Information regarding Grindstones

If grinding this on a high speed grinder, be sure to manage the temperature so that the temper is not lost due to overheating. If there is a carbide insert, DO NOT cool by dipping in water. This will cause the carbide to crack due to shocks. Otherwise, cool by dipping as needed in water.

For resharpening, a contour gauge like shown below is recommended. One should be made for each tool, and it should be numbered to match the tool's number.

More Information

Books & Papers

The definitive source is Leo J. St. Clair's book from 1952 titled, Design and Use of Cutting Tools. He was working in the industry as it was changing from HSS to carbide, so both are covered well. His experimental data helps validate or disprove many theories. Unfortunately, this book is hard to find.

Videos & Presentations

Tormek Tool Rest SVD-110 (YouTube video)

Tormek AngleMaster WM-200 (YouTube video)

Web Sites

Conversion of Brinell vs. Rockwell hardness measurements.

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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.