Sharpening Handbook

Because sharp enough

... usually is not

Metal Lathe Tools: Boring Bars

Carbide vs. HSS
Material	Compressive Strength	Shear Strength	Max Usable Temp*
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.

You know what it's supposed to look like when you're done. Do what you have to do to make it look like that.

Unknown Old Machinist

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 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.

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

Tool Shape - Boring Bar

Back Rake	Side Cutting Edge Angle	Nose Radius	End Cutting Edge Angle	Side Rake Angle	Side Relief Angle	Side Clearance Angle	Comments
-10°	10°	1.5 mm (¹/₁₆”)	10°	-5°	5°	7°	Angles shown are the recommended effective angles, not the ground angles.

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.

Contour Gauge

For resharpening, a contour gauge like shown to the left 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.