Broaching with Internal Hole Broaches requires no Shims or Bushings. Round, Square, Hexagon and many Special Shapes are designed to finish in one pass, in cast or drilled bores requiring a through hole finish. The starting hole must be drilled square with the face of the work. Square and Hexagon Broaches, 1/4″ and 6mm or smaller, should be gripped by the shank in an adapter to prevent deflection and breakage. All individual stock Broaches have recommended Minimum and Maximum Length of Cut guidelines which should be followed. Workpieces may be stacked to establish the Minimum Length of Cut, or to improve the efficiency of the operation as long as Maximum Length of Cut is not exceeded. Proper nesting and clamping of stacked parts is vital when this approach is taken. The workpiece must be solidly fixed or nested perfectly square with the baseplate and ram face. Make sure all square and parallel surfaces on the face of the ram and baseplate remain true. It is essential to maintain a rigid set-up at all times and caution should be taken when stacking parts to maintain the integrity of the set-up. Never attempt to exceed the Broach’s specified Maximum Length of Cut. Do not use a dull Broach, this may result in poor finish or damage to part and increases the danger of breakage. At the beginning of a cut, be sure the Broach is centered under the ram. Proper alignment is important. After the Broach starts to cut, back off pressure on the ram allowing the Broach to center itself, providing for better alignment. If the Broach moves out of alignment after starting cut, back off the pressure on the ram and align the broach itself. Repeat this procedure during successive cuts. This will assure a perfectly straight broached hole..
- Pilot Holes: Properly drilled pilot holes are essential for a true and clean cut. Never use a dull or poorly sharpened drill to make pilot holes.
- Select desired Broach. Confirm the bore of workpiece is equal to pilot diameter of broach. (The use of a ram adapter is advised with all Round, Oval, D-hole Broaches, and for Square and Hexagon Broaches 1/4″ and 6mm or smaller).
- Insert pilot into bore of part.
- Ram Speed: Always use proper ram speed to prevent chatter marks and edge wear. (See Metals Handbook–Vol. 3 “Machining”.)
- Apply pressure to the Broach – back off pressure on the ram allowing the Broach to center itself, providing for better alignment. If the Broach moves out of alignment after starting cut, back off the pressure on the ram and align the broach itself – reapply pressure to push Broach through the work.
- Clean Broach using a stiff brush to remove chips from cutting section.
- Repeat steps 3 thru 7 for subsequent parts.