Selecting carbide inserts.

Author:Rose, Steve
Position:Shop talk

There are many important concepts to cover when training people in CNC machining. One of the most important and most confusing is the understanding and selecting of carbide inserts.

Carbide inserts offer so many choices that machine operators can get overwhelmed. Some of the choices include negative rake inserts versus positive rake inserts and the combination Pos-Neg geometry inserts; coated versus uncoated, chip breaker styles and the different tool nose radius options.

Our training goal is to show how these options can solve different machining problems. Once an operator can select a tool or insert to solve a problem, they can use that knowledge to select tooling for a specific application and avoid future problems.

The tooling catalogs do a good job of explaining the nomenclature of the various types of carbide inserts. Problem is, too often the catalogs are not made available on the shop floor. The programmers and tooling staff need the catalogs so most operators never get to see them.

The most important piece of information about any insert is the tool nose radius. The TNR affects the geometry of the part, so this concept is the one stressed in our training classes.

I've seen many instances of operators changing an insert and substituting an incorrect insert nose radius. We all know the machinists' theme song, "My Way", so when an operator wants to use a coated insert, he or she will pick a coated insert without regard to the nose radius. As most operators are not familiar with the ANSI nomenclature system and there is not often a tooling catalog available, many take the attitude, "Let's stick it in the machine and see what happens."

There is nothing wrong with wanting to change an insert in hope of finding a better choice, but there is danger in inadvertently changing the TNR.

If an incorrect TNR is used, the first thing the operator notes is that the lathe tool offset needs to be adjusted by a larger amount. Often the operator adjusts the offset and gets back to work. Having missed the first warning sign, we hope that during inspection, the operator notices that the...

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