Cutting Edge Height vs. Insert Thickness

Originally written by Charles Colerich for Horizon Carbide
Edited by Bernard Martin

The Industry Standard thickness tolerance for “G” (ground) and “M” (molded) class Inserts is ± .005. This standard was established before the introduction of molded chipbreakers and creates confusion regarding double sided turning Inserts.
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Negative rake chipbreaker Inserts are nominally thicker than flat top Inserts. An elevated pad on both sides of the Inserts keep the unused edges from contacting the tool holder or shim seat. The tolerance refers to the cutting edge height rather than the Insert thickness.

​The easiest way to measure the cutting edge height is with a height gage on a surface plate.

Tool Holder Insert Height

The Industry Standard for Insert height in tool holders is ± .010. This creates a Center Height range of .030 (± .015) when combined with the Insert tolerance of ± .005.

​For best results on smaller diameter parts and/or small nose radius Inserts the center height should be adjusted to a maximum of ± .001.
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Insert Cutting Edge Height

Insert heights for most negative rake tool holders are set using .031R Gage Inserts.

There are no geometry standards for negative rake 35° tool holders. Insert rake angles vary between manufacturers and range from -6° to -13°.

This causes problems with inserts having a nose radius other than .031R. Center Heights for smaller radius inserts drop due to the negative rake angles. The drop is significant with 35° and 55° Negative Rake inserts.

​Horizon DNGP and VNGP Inserts are ground to the low side of the height tolerance to reduce center height problems.

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Farewell and Parting

28 March 2025. Editors Note: This article, "Cutting Edge Height vs. Insert Thickness," was authored by the late Charles Colerich of Oakland, California. Charles was a distinguished cutting tool engineer, renowned for his expertise in developing high-positive geometries for machining stainless steel and high-temperature alloys. His consulting work with several manufacturers from Horizon, Kennametal and numerous other companies significantly advanced the field of cutting tool technology. Beyond his professional achievements, Charles was a valued member of the cycling community, known for his contributions under the username "verktyg" on various bicycle forums. His passing is a great loss to both the engineering and cycling communities.​