Metal Lathe Tools : Boring Bars

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.

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

Carbide vs. HSS
Material Comp- ressive 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

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 in)
10° -5° 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.

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.

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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