Slater Tools: Number one for Rotary Branding

Getting More from your Shop Floor

Posted: December 3, 2013

A fast and efficient machining method, rotary broaching is used for making squares, hexes, splines, serrations, keyways, Torx-type and a range of many other internal and external polygon shapes on a workpiece. If your shop uses machines such as CNC lathes and mills, Swiss-type machines and machining centers, then you already have the capability to use this efficient technique and benefit from it as an alternative to outsourcing or having to use slower and more costly methods of producing a shape in a part.

Small and large machine shops alike, with a variety of customers in varying industries, benefit by having a rotary broach toolholder on hand. When new applications arise, simply switch broaches to run a different form with minimal effort. Rotary broaching has seen increasing demand in recent years from industries such as medical, aerospace, automotive and fasteners where special shapes are machined into various materials. For example, bone screws used in orthopedic implant operations, and aerospace port connectors, are produced quickly and in one pass.

One significant advantage of rotary broaching is that it can be performed on any CNC lathe, mill, machining center or other turning machine. In most cases, rotary broaching can be performed at the same time as other turning operations, increasing efficiency and profitability during production, without sacrificing accuracy. Unlike conventional broaching, where a series of stepped polygon forms are pushed through a hole until the desired size and form is achieved, the rotary broach cuts the full form, one corner at a time.

Additionally, broaching into a blind hole is possible with rotary broaching. Using a toolholder with a built-in one-degree offset (relative to the workpiece center line), a controlled wobble action is created as the broach sequentially cuts from tooth to tooth upon engagement with the workpiece. The resulting benefits are reduced cutting forces, increased tool life, tight tolerances (0.0005"), fast cycle times (1500 rpm and 0.006 ipr on average) and the ability to eliminate secondary operations on another machine.

Because of the free rotating spindle on the rotary broach toolholder, live tooling is not needed to rotary broach. On a mill, the rotary broach toolholder rotates in the machine spindle while the broach and the part are stationary. On a lathe, the toolholder body remains stationary while the free-spinning broach rotates in sync with the part.

The best applications for rotary broaching are small forms (0.028" up to 2.00" diameter) that need to be machined at shallow depths. A general rule of thumb on recommended depth is not to exceed 1.5 times the minor diameter of the form. Materials such as plastics, aluminum, brass, alloys, and stainless steel are ideal for rotary broaching. Difficult materials, like titanium, can also be successfully broached with enhanced broaches in a variety of coatings (TIN, TICN and TIALN) and substrate materials (M-2 HSS and PM-4).

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