8 Steps to Successful Rotary Broaching with Slater Tools' Internal Rotary Broaches
1. Determine the BROACH SIZE.
For nominal socket sizes, standard Slater broaches are based on the ASME Maximum for "Socket width Across Flats" to provide allowance for key clearance and broach re-sharpening. For common applications, the "E-Length" of standard Slater broaches will be adequate for the required broach depth. For non-standard requirements, Slater provides fast delivery of special sizes and lengths.
2. Select the appropriate BROACH TOOL MATERIAL.
Slater Tools' standard broaches are made of M-2 High Speed Steel. Rotary broaches are also available in PM-4 material, which is a powdered metal with a tighter grain structure for higher wear-ability. T-15 cobalt material is also available for all Slater Tools broaches. For longer tool life, coatings such as TIN (Titanium Nitride), TICN (Titanium Carbonitride), and TIALN (Titanium Aluminum Nitride) are available for both internal and external rotary broaches.
3. Drill the correct PILOT HOLE diameter and depth.
Pilot hole diameter: Pilot holes are required for internal broaching. The pilot hole diameter must be at least equal to the "Across Flats" dimension of the internal broach. Often, hexagon holes are not required to be "full form". In these cases, a larger pilot hole will reduce the required broaching pressure and allow for longer tool life. Click here to see the chart for recommended pilot hole sizes for standard Slater broaches.
Pilot hole depth: The pilot hole depth must be greater than the depth to be broached. It must be deep enough to allow for chips to accumulate without excessive packing. If the chips must be removed, this can be done after broaching with a drill or boring tool. A recess at the bottom of the pilot hole will allow the chips to break cleanly. The recess diameter should be larger than the "Across Corners" dimension of the broach.
4. Machine the LEAD CHAMFER onto the work piece.
A 45° chamfer, slightly larger than the "Across Corners" dimension of the broach must be provided. Click here to see the chart for recommended chamfers for standard broaches.
5. If using an adjustable rotary broach tool holder, CENTER the tool holder.
For proper operation, the adjustable tool holder must be aligned for the length of the broach per the instructions provided with your Slater rotary broach tool holder. Since standard Slater broaches have a common length, this procedure may not be required with every use of the tool holder. Click here to view set-up instructions.
6. Determine the required THRUST POUNDS.
Click here to see the chart for approximate thrust pounds of standard broaches in various materials. Confirm that your machine tool is capable of producing about 25% more than the required thrust. Remember, as the pilot hole diameter is increased for a given broach, the required thrust is reduced.
7. Determine the SPEED AND FEED rate.
Click here to see the following chart for recommended speeds and feeds for internal rotary broaching in various materials. Consider these as starting points, as your machine tool, your part requirements, and other circumstances will be unique to you. Use a minimum feed rate of .004".
8. Determine your FLUID/COOLANT requirements.
Fluids and coolants play a minor role in rotary broaching. Any type of water or oil based fluid is acceptable. The chip from rotary broaching is the flowing type with very minimal heat generation.
When rotary broaching internally in a blind hole, fluids should be applied on the tip of the broach prior to contacting the work-piece, not inside the pilot hole. Trapped fluid may not be able to escape, creating hydraulic resistance, which will prevent full depth broaching. Slater Tools does offer vent holes and double vent holes for customers who are concerned about trapped fluids.