Fixed Cycles on the Mill - 1: Overview
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
Fixed cycles on a CNC mill are primarily used for hole machining. Types of hole machining include center drilling, counter sinking, drilling, reaming, counter boring, boring, right hand tapping, and left hand tapping.

A hole can be as simple as a 1/4 inch diameter hole drilled through the part. Other holes could be more complicated by being: a blind hole, a low tolerance hole, or stepped hole.
Fixed cycles (commonly called canned cycles) make programs shorter; much faster to program; easier to understand, easier to read, easier to troubleshoot, and with less chance of error.

The following example shows the usefulness of canned cycles. If you were to drill the four holes in the plate shown on the right, here is how you would have to program without fixed cycles:

Assume Z-1 will drill through.

  • G90 Z.05
  • G00 X2Y2
  • G01 Z-1 F20.
  • G00 Z.05
  • X2Y8
  • G01 Z-1
  • G00 Z.05
  • X8Y8
  • G01 Z-1
  • G00 Z.05
  • X8Y2
  • G01 Z-1
  • G00 Z.05

Now the same program with a G81 canned cycle

  • G90
  • G81 X2 Y2 Z-1. R.05 F20. G99
  • X2Y8
  • X8 Y8
  • X8 Y2
  • G80

Notice that the 13 line program has been replaced with a much simpler 6 line program and that every new hole needs only one line of code.

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label: fixed cycles, G codes, words, canned cycles G73, G74, G76, G81, G82, G83, G84, G85, G86, G89