What Are the Functions of a Cutting Tool in CNC?


Many different types of cutting tools exist for CNC machines. CNC, or computer numerical control, machines use a program to move cutting tools into place to cut material to form a part. Each tool serves a different function, so it is imperative that a machinist or machine operator understand what he does and what operations each is capable of performing.

End Mills

  • End mills are used to cut metal and other materials in CNC machines. Milling machines use roughing end mills to remove large amounts of raw material to create the rough shape of the part itself. The machine then uses a finishing end mill to complete the part to size as defined in the blueprint. End mills come in various sizes as well as materials including high-speed steel, cobalt and carbide. Carbide end mills are the hardest and are used for finishing end mills, while cobalt end mills are used mostly for roughing models.

Insert Cutters

  • Insert cutters are used for cutting raw material in a CNC lathe. The tips, also known as inserts, are made of carbide and are held in place in steel shafts with a center screw or retaining clip. The tips can be rotated as they become dull and new tips can be placed in the tool holder when old ones break or all sides have been used. The inserts have various chip-breaking designs in order to produce a nice finish. There are inserts that are used for roughing as well as finishing.

Drill Bits

  • Drill bits are used in both CNC lathes and mills for drilling holes of various sizes. Drill bits are held in drill chucks in most cases but can be put in rigid CAT 40 or CAT 50 holders when used in CNC mills. Drills come in various sizes as well as materials including carbide and high-speed steel. In CNC mills, the drill bit and holder spin at various speeds depending on the material to be drilled but are stationary in lathes as the material itself is spinning when cut in a CNC lathe.

Boring Bars

  • Boring bars are used mostly in CNC lathes and open up holes that are cut earlier in the program or for material that already has an existing hole of some kind. They are similar to insert cutters as they have removable tips that can be turned or replaced when dulled. The shaft of the boring bar is usually made of high-speed steel or carbide. They are placed in holders and need some clearance to fit into the existing hole to be truly effective. The same insert is often used for the roughing and finishing operations.


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