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How to Understand Machining Carbide Insert Classifications

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There are many different types of carbide inserts available for use with specially made tool blocks. Used primarily in manual and computer numerical control lathes, these inserts are identified by a series of letter and numbers that have a particular meaning. In order to classify them correctly, you must know what each letter and number means, and how it will impact the machining operation you plan on performing.

Look at the first letter in the sequence. This letter dictates the shape of the insert. Carbide inserts use shapes lettered A through X, with some letters omitted for clarity. The most common shape used for lathe work is C; this is an 80-degree diamond shape. V, also a very common shape, is a 35-degree diamond with a thinner tip that is nevertheless well suited for precision profile work.

Note the second letter in the carbide insert designation. This letter notes the amount of clearance bellow the tip of the insert. The more clearance, the more likely it is that the carbide insert will chip under pressure. Use the right amount of clearance for the job at hand, making sure there is enough for large angled cuts, but not too much, as to leave the tip vulnerable to failure.

Identify the fourth letter in the carbide insert sequence, as this letter indicates the chip break properties. The chip break is the way the chip is expelled from the insert. If you use the wrong type of chip break, you may have unwanted chip buildup, which will cause tolerances to be lost during machining. The G chip break is the most common, as it offers two-sided chip break ,as well as good overall chip evacuation during heavy roughing.

Use the first number in the sequence to determine the size of the carbide insert. Since there are many types of insert holders, you must use the correct size for your particular holder, regardless of the other points of designation. Half-inch inserts, noted with a 4, are 1/2-inch in size and fit standard tool blocks used in CNC lathes.

Check the second number in the sequence to determine the thickness of the insert. Insert holders should only be used with the insert that is of the correct thickness, as inserts too thick or too thin will result in inaccuracies. As the divot for the insert is set at a specific depth, using an insert of the incorrect size may result in catastrophic tool failure.