One of most used canned cycles of fanuc cnc control is G72 Facing Cycle.
G72 facing cycle is used to remove extra material from the component face.
As G71 turning cycle takes cuts in longitudinal direction (Z-axis) to remove extra stock, same way G72 facing cycle takes cuts in traversal direction (X-axis).
As canned cycles makes a cnc programmer and cnc machinist life easier by making programs shorter, easy to edit, debug and easy to try-out while setting a component.
The same way Fanuc G72 facing cycle with it’s few parameters give us full controls over removal of extra material from component face.
Another article about G72 facing cycle with program exmaple code is here CNC Fanuc G72 Canned Cycle Facing
Fanuc G72 Facing Cycle Format
G72 W… R… G72 P… Q… U… W… F… S…
First Block of G72 Facing Cycle
W -Depth of cut.
R – Return value after a cut is complete (retract amount after each cut).
Second Block of G72 Facing Cycle
P – Contour start block number.
Q – Contour end block number.
P & Q -The cnc program blocks between the P block number and Q block number will be repeated until the end dimension is not met.
U – Finishing allowance in x-axis.
W – Finishing allowance in z-axis.
F – Feed-rate (overrides the feed-rates given between P block and Q block)
S – Spindle Speed (overrides the spindle speed given between P block and Q block)
The benefit of using F (feed-rate) in G72 second block is that during facing cycle machine will use this feed-rate, and will ignore any feed-rates given between P block and Q block program.
The feed-rate given between P block and Q block program will only be used if you call G70 Finishing Cycle later in program with same P block and Q block numbers.
This is very handy way gives cnc machinist opportunity to keep different feed-rates for “rough facing cuts” and “final finishing cut”.
S (spindle speed) works the same way to keep different speeds for roughing cuts and finish cut.
Fanuc G72 Facing Cycle Working
To better understand below is an image which shows how tool travel while cnc machine is executing G72 facing cycle.
G72 W(d) R(e)
G72 P_ Q_ U(u) W(w) F