The Wobbling Broach
A rotary broach is a special type of surface broach that is not commonly used, but does have its advantages. One of the rotary broaches advantages include its ability to be used on common machine tools, instead of requiring a specialized broaching machine. Rotary broaching can also be performed on both milling machines and screw machines. It does this by using a tool holder to attach onto the other machine. The process is capable of producing accurate forms at a speed of mere seconds. However, rotary broaches do not make as accurate of cuts as push or pull broaches.
There are many tools available for rotary broaches. For smaller European machines, an adjustment-free Swiss type broach is available. This type of broach is manufactured with consideration for the smaller clearance of smaller machines. A regular adjustment-free type broach is capable of accepting an array of forms. For larger forms that require more speed, there is a heavy duty tool available. There are also tools that focus on accuracy for precision machining.
Rotary broachers are offset by 1 degree to produces a rotating edge. The rotation of either the workpiece or the tool holder makes it appear as if the broach is wobbling. Hence the nickname, wobble broaching. In order to cut the desired shape out of a workpiece, the tool makes one revolution. They are typically equipped with air vents to release pressure and are manufactured from M2 high-speed steel. Rotary broaches aren’t commonly used but are preferred with working with external radial forms. The standard rotary broach is also capable of being modified to have, among other things, custom flat-to-flat dimensions, no air vent holes or double air vent holes.