Internal Broaching Part Preparation

Pre-Drill Hole Diameter:

• A pre-drill hole is required for internal broaching.
• The pre-drill hole must be at least equal to the minor diameter of the broach. It is strongly recommended to open the hole diameter larger than the minor diameter.
• See below formulas for recommended pre-drill hole diameters of hex and square forms.

Pre-Drill Hole Depth:

• The depth of the pre-drill hole must be greater than the broaching depth to allow for chips to accumulate and avoid excess packing.
• If chips must be removed after broaching, it can be done with a drill or boring tool. A recess at the bottom of the pre-drill will allow the chips to break cleanly. The recess diameter should be larger than the major diameter of the broach.
• It is recommended to have a pre-drill depth of 1.75 x depth of broached area.

Lead Chamfer:

• A 45° lead chamfer must be provided for successful internal rotary broaching, going from the major diameter to the minor diameter of the form.

External Broaching Part Preparation

Pre-Turn Diameter:

• Pre-turning the diameter of the workpiece is required for external broaching.
• The pre-turned diameter must be smaller than the major diameter of the broach.
• It is recommended to turn the workpiece diameter to the smallest allowable diameter so the broach will clear on the major diameter. Allowing for more clearance will reduce the required broaching pressure and increase tool life.
• See below formulas for recommended pre-turn diameters of hex and double-hex forms.

External Form Depth:

• Maximum recommended broach depth is 1.5 x minor diameter of form.
• A back-chamfer or undercut will allow chips to break cleanly. The undercut should be approximately .0625" wide.

Lead Chamfer:

• A 45° lead chamfer must be provided for successful external rotary broaching, going from the minor diameter to the major diameter of the form.