Post Processor Engineering

Canned Cycle Handling in Custom CNC Post Processors

Canned cycles turn many lines of drilling motion into one short, editable block. But every controller implements them slightly differently, and the post must match exactly.

April 29, 20267 min readENGIMANDI CNC Team

Standard milling cycles (FANUC-type)

CodeCycle
G81Spot / simple drilling
G82Drilling with dwell at bottom
G83Peck drilling (full retract)
G73High-speed peck (chip break)
G84 / G74Tapping right-hand / left-hand
G85, G86, G89Boring variants
G76Fine boring with spindle orient and shift
G80Cancel cycle

G98 vs G99 retract

G00 Z50.            (initial level)
G99 G81 X10. Y10. Z-12. R2. F150.   (retract to R between holes)
X30.
G98 X50.            (retract to initial level - clears a clamp)
X70.
G80

The post chooses G98 or G99 based on clearance settings in CAM, so tools don't hit clamps or bosses between holes.

Cycles on other controllers

  • SINUMERIK: CYCLE81–CYCLE89, CYCLE84/CYCLE840 for tapping, often with MCALL.
  • Heidenhain: CYCL DEF 200, 203, 205, 207 with Q parameters.
  • Okuma and others: own formats and parameter orders.

Tapping details

  • Rigid tapping activation (e.g. M29 on some FANUC machines).
  • Feed = pitch × rpm (per minute) or pitch (per rev mode).
  • Peck tapping support on some controllers.

When to expand cycles

If the controller lacks a cycle, or the machine is in a mode where cycles aren't allowed (for example certain multi-axis modes), the post outputs equivalent G0/G1 moves instead. This is a post property, not a manual edit.

Cycles keep programs short and editable, but only if the post outputs every parameter correctly.

Cycle handling in posts

See our CNC post processor development service and subprogram and macro generation.

EM
ENGIMANDI CNC Team

We develop, customise and commission CNC post processors for Fusion, NX CAM, Mastercam, SolidCAM and other CAM systems.