An Efficient Way to Create Non-Round Shapes


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The rotary broaching process creates a non-round shape on the inside or outside of a part. With the right preparation, knowledge of appropriate feeds and speeds, and proper alignment, complex forms such as splines, hexes, serrations and other shapes can be quickly machined on a CNC lathe or mill, manual machine or screw machine.

During rotary broaching, the head of the broaching holder is offset from the centerline of the chuck or collet on a 1-degree angle. By synchronizing the rotation of the spindle and broaching drives, this orientation creates a shearing effect around the edges of the form being cut—essentially only a section of the form is being cut at any given time—which greatly reduces the amount of cutting pressure needed to form the desired feature.

For most applications, M2 high speed steel is the best material for broaches to be made from. However, for machining tougher materials, such as stainless or hardened steels or exotics, the broach should be made from T15, because of its better wear resistance compared with M2.

Broaching should be done with an oil-based coolant, which will provide more lubricity to the broaching process and could extend the tool life by as much as 2 to 3 times.

To learn more about the rotary broaching process, its speeds and feeds, preparing the workpiece and troubleshooting, read “The Basics of Rotary Broaching.” 

To learn about how adding rotary broaching to an existing Swiss-type turning center is a cost effective method of increasing production, read “Turbocharge Swiss-Type Turning with Accessories.”