How to Rotary Broach

What is Rotary Broaching

Rotary broaching, also known as Wobble Broaching, is a unique process of cutting polygon

forms into a work piece using any vertical or horizontal spindle machine such as a CNC or manual turning lathe, screw machine, mill and other drilling machines.  These forms can be cut into either a blind hole or a through hole.

The benefits or rotary broaching include speed, price and efficiency.  With rotary broaching these is no need for an expensive secondary operation such as EDMing or conventional broaching.

Although this process can be used in a variety of applications it is prominent in the medical, aerospace, automotive, fastener and plumbing industries.

How Rotary Broaching Works

There are only a few steps required to successfully rotary broach a polygon form into a work piece.  Once your part is turned you will need to chamfer on center and pre-drill a pilot hole.  Next you will broach the form and then drill out the chips that accumulate at the bottom of the part.

As the rotary broach tool is being fed into the work piece it chisels or scallops the form into the part until the required depth is reached.  This is where the term "wobble broach" comes from.

You can quickly rotary broach such shapes listed below into brass, stainless steel, aluminum, titanium, plastic and other materials:

    Hexagon (Hex)

    Square

    Torx

    Rosan

    Serration

    Keyways

    Double Square

    Double D

    Double Hex

    Involute

    Spline

    Spur Gear

    J500

Other custom polygon shapes can also me designed and manufactured according to your specifications.

Tools Required to Rotary Broach

These are only two items required for the rotary broaching process:

1. Rotary Broach Tool Holder; and
2. Rotary Broach

These rotary broach tools can be purchased online from Polygon Solutions.

Rotary Broaching Process

Rotary broaching can be completed within seconds with just a few simple steps as outlined below.

Chamfer Part

First you will need to add a 90 degree lead chamfer slightly larger than the across the flats dimension.

Pre-Drill Pilot Hole

Next you will need to pre-drill a pilot hole approximately 3% larger than the across the flats dimension of the rotary broach.  For example, if you are using a 1/4" hexagon rotary broach tool then a .260 pre-drill is recommended.  If you are broaching a blind hole you will need to pre-drill 2 times the depth that you intend to broach to allow for chip accumulation.

Rotary Broach Form

Now it is time to broach the form into your work piece.  Speeds and feed vary depending upon the material being broach, the size or the broaching tool and the depth you are broaching.  This step is completed within seconds.

Remove Chips

Whether you are broaching a through hole or a blind hole it is always a good idea to go back into the part with your pre-drill and remove any chips that may be built up in your part.  To achieve this simply run your pre-drill program again.

Deburr

Sometimes after the broaching process is complete you will need to deburr your chamfer by running your chamfer program again.  This will ensure that any burrs left by the broaching process are removed.

Tips

• When broaching tougher material such as stainless steel or titanium it is recommended that you use a rotary broach tool made from M-42 or PM T-15.

• To add longevity to your broaching tool coatings such as Titanium Aluminum-Nitride, Titanium Carbo-Nitride or Titanium Nitride can be added to any broaching tool.

Broaching Limitations

Rotary broaching is not suitable for every application.  There are limits on the size of the diameter that can be broached as well as the depth that can be broached.  For most cases you can not broach a diameter larger than 1".  The maximum depth you can broach will depend upon your broach size.  Typically you can broach up to two (2) times the dimension across the flats of your broaching tool.  For example, if you are using a 3/8" Hexagon rotary broach you could broach a depth of .757".