Gee Seven Two: Rough Facing Canned Cycle
G72 Commands the machine to carry out a “Canned Cycle” that is used to rough FACE a part. Typically from Far to Near turning cycle with a finishing allowance. Very similar in execution to G71 with some important differences. The Modus Operand is all about facing in the X axis with moves to increase the cut made in the Z axis (so in effect, the opposite of G71).
It is possible to turn a part using G72 instead of G71 but tool geometry would typically be incorrect and far less efficient.
Let’s look at our project item we want to make.
From above
This time we will be cutting in the direction of the red line/arrows.
The G72 canned cycle block will remain in a similar layout.
- G72 W1.0 R1.0
- G72 P100 Q200 U0.2 W0.2 F0.25
First Line:
First the W value, This is the depth of cut used in the Z axis NOTE: Z, not X (hence why it is in red)
Then an R value, at the end of each cut pass, is the amount the tool will retract to prevent it dragging on the way back to the start point.
Second Line:
G72 continues the canned cycle function.
P100 is the first line of the shape we are defining
Q200 is the last line of the shape we are defining
U is the finishing allowance in the X axis
W is the finishing allowance in the Z axis
F is the feed rate we wish to use
Ok so we have set up the initial tool starting point and given G72 all it’s needed settings. Now we have to tell the machine what we want made. So how about the shape below? Remember we are “drawing” the finished shape NOT doing a line by line construction.
- G00 X51.0 Z3.0
- G72 W2.0 R0.5
- G72 P100 Q200 U0.5 W0.2 F0.25
- N100 G00 Z-5.0
- G01 X50.0
- G01 X46.0 Z-3.0
- G01 X20.0
- G01 Z-1.0
- G01 X18.0 Z0.0
- N200 G01 X-1.0
You will notice that the final position in X is a minus value, that is past the centre of the job, there are a couple of reasons for this, 1: you need to make sure you lose the pip in the middle that the tool radius can cause and 2: it’s good practice to do so, so that when we come to doing part off jobs we ensure a complete and clean cut.