Index Punch 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 finished form. It is strongly recommended to open the hole diameter larger than the minor diameter.
• For keyway and single point broaching, the pre-drill hole must be equal to the finished keyway bore or minor diameter

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.
• It is recommended to have a pre-drill depth of 1.75 x depth of broached area.
• For full form or two corner punch broaching:
• A recess at the bottom of the pre-drill is recommended, which will allow the chips to break cleanly. The recess diameter should be larger than the major diameter of the finished form.
• If chips must be removed after broaching, it can be done with a drill or boring tool.
• For keyway and single point broaching:
• A recess at the bottom of the pre-drill is mandatory. The diameter of the recess should be larger than the major diameter of the finished form

Lead Chamfer:

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