How to Make Keyway Broaches

Written by liz tomas
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A keyway broach tool is used to produce the keyway broach or opening found on a timing pulley or gear. Broaching involves pulling or pushing a cutting tool known as a broach through or over a surface. Keyway broaching is a type of internal broaching that will require an opening or starting hole in the piece for the keyway tool to be inserted. The keyway broach tool has many teeth that will progressively make a deeper cut. This type of cut can be made with a square cutting blank or lathe, but a keyway broach tool provides the best accuracy. Ensure that the keyway broach you make is the proper size for your gear.

Skill level:
Challenging

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Things you need

  • Drill with assorted drill bits
  • Press machine, pulley or similar machine
  • Bushing
  • Keyway broach tool
  • Lubricant

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Instructions

  1. 1

    Use a drill with a sharp bit to drill a pilot hole into the item you are broaching. The pilot hole acts as a guide for the keyway broach tool. Make sure that the item is fastened securely in place so it does not move and that the pilot hole is drilled straight, not at an angle.

  2. 2

    Insert the correct size bushing for the bore and insert the bushing into the bore of the machine. Keyway broaches can cut a keyway as small as two millimetres up to 18 millimetres. Bushings can be inserted into the bore of a gear, collar, pulley or similar work piece. Make sure you keyway broach fits the machine bore.

  3. 3

    Insert the keyway broach into the bushing slot and make sure the alignment is correct. Misalignment can cause the piece to break, deflection of the broach or drifting when cutting. Ensure that the piece is solidly nestled and is squared with the ram face and the base plate of the machine. The broach should be aligned with the press ram direction of movement.

  4. 4

    Place the entire bushing and broach tool assembly into the press. Lubricate the broach tool and push it through the item. When cutting through steel, a water-soluble coolant of cutting oil is recommended as a lubricant. Cutting through brass requires water or no lubricant and cast iron needs no lubricant. Use tap cutting fluid designed specifically for aluminium when cutting through aluminium. Make sure you lubricate the sides and back of the broach tool as well as the front.

  5. 5

    Remove any cuttings from the broach tool before letting it move back through the item again to return to its starting position.

Tips and warnings

  • Use shims for cutting specific depths in the keyway. The broach tool is inserted into the shim and then into the item. At a specific depth, the shim will stop the keyway broach tool from moving further and creating a larger opening.

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