Blind Keyway Broaching

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Definition of a Blind Keyway

  • You can have a through bore, but still have a blind keyway
  • A keyway is considered blind if it stops in the middle of material
  • To use CNC Broach Tools you must have your blind keyway end in an appropriate groove or cross hole relief
  • the keyway must end "in air"
  • Be aware that you can have a through keyway but be machining it out of bar stock. Which means you'll be machining a blind keyway and will still need adequate relief space

CNC Mill Broaching A Blind Keyway

  • When cutting a blind keyway in a mill, gravity is not working with you
  • The material you are cutting can pile up into your relief area causing a crash
  • We highly recommend a cross-hole relief when using a mill because the coolant can flush your chips out either side
  • With a groove relief your chips can pack the groove, resulting in a crash
CNC Mill Broaching a Blind Keyway

NOTE:

We do not recommend that you taper or radius out of a blind keyway. This will result in a crash. You must have an adequate groove or cross-hole relief area

CNC Lathe Broaching a Blind Keyway

  • In a lathe, gravity assists with chip evacuation
  • A groove or cross-hole relief is accepta

Tips For Relief

  • Make sure your cross-hole is larger than the keyway
  • If your groove relief is not radially deeper than your keyway, you will “bottom out” and crash
  • You will be programming the insert cutting edge to stop approximately .080” past the end of the keyway so that you do not decelerate in the keyway and create a taper
  • Past this .080”, you need space for your chip to drop away without putting pressure back on the face of the insert

Example

Q: If a 3/16 wide keyway with a 2.5” Length of Cut & has a 3/16" wide groove relief, is that enough?

A: Probably not. Don't forget that you do not have an actual 3/16 relief as you are stopping .100" past the end of the keyway to leave space for deceleration. If you stop to close the end of the keyway you can decelerate in the actual keyway leaving a taper or lip. How much space you need for deceleration depends on your machine. SO, if you are stopping .100” into a .1875 groove that only leaves you .0875” of space to jam 2.5” of material. Not enough.