Instructions

g40 g20 g90 g00 g80 z2
x0 y0
g81 x2 y1 z-0.50 r0.010 f3
x3
x4
g00 g80 x0 y0
%
The g82 command
G82 is intended for drilling when you want a dwell at the bottom of the hole. (I find
this a bad idea when drilling, because some of the more exotic metals like stainless steel
may work harden and cause the drill to become dull sooner than it should.)
1. Move the z-axis only at the current feed rate to the z position.
2. Dwell for the given number of seconds. The length of the dwell is specified by
a p# designation in the g82 block and time entered would seldom be more than a
second.
3. Retract the z-axis at rapid rate to clear z. The motion of a g82 canned cycle
looks just like g81 with the addition of a dwell at the bottom of the z-axis move.
Example:
%
g90 g40 g20 g80 g00 z2
x0 y0
g82 x4 y5 z-0.50 r0.010 p0.2 f3
g00 g80 x0 y0
%
The new command to learn is command is p.
The g83 command
G83 is intended for deep drilling because you’ll break the drill if you don’t retract it
periodically. When you retract the drill it allows the chips to fly off and lets cutting fluid
wet the bit and the work before they gall or weld themselves to the drill bit. The general
rule when using a CNC machine is to have the drill cut no deeper than its diameter
without retracting it for the above reasons. This is called peck drilling.
The peck drilling cycle should also be used when center drills are used to create starting
points for your drills. Center drills twist off very easily because their drilling section is
not relieved as much as a drill is. This is done to force the drill to seek center; however,
they become very vulnerable to breakage. The z-axis should be retracted when center
drill’s depth has reached 60% of the needed depth. Note that drills will wander by a far
greater amount than you can imagine (especially if they are old and dull) if a center or
spotting drill isn’t used to develop a starting point. I prefer spotting drills (short drills
with a 90 degree point that cuts to center) over center drills because there is no small
point to twist off. They also have a proper chamfer angle and a faster machine operation.
This cycle takes a q value given as an increment value. This represents the increment of
movement along the z-axis before the drill is retracted to clear the chips. Again,
machinists refer to this as peck drilling.
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