Accurate CNC 360 Milling G-Code

N1 G90
N2 G20
N3 T0 S10000 ( 0.0610"/1.549mm DRILL Hole : 0.060"/1.550mm, {Z-0.00500"/-0.127mm, TH07} Pin1-1.550mm )
N4 G0 X4.75212307 Y3.76442850 (Stop-point)
N5 G91 G81 X0.39370079 Y0.39370079 Z-0.08000 R0.05000 F3.0
N6 G90
N6 T1 S10000 ( 0.0807"/2.050mm DRILL Hole : 0.080"/2.029mm, {Z-0.00500"/-0.127mm, TH08 } Guide Pin-2.050mm)
N4 G0 X4.75212307 Y3.76442850 (Stop-point)
N7 G91 G81 X0.39370079 Y3.60236221 Z-0.08000 R0.05000 F3.0
N8 X1.14173228 Y0.0000
N9 X0.000007 Y-3.20866142
N10 G00 Z0.05000

Hi guys, The G91 and G81 g-code seems not to work when I import it into the milling machine. It does not drill through the object, instead it increase the "Z" value. How do I edit the code so that it can drill through the object?

Hi,
the G91 preceding the drill cycle puts the machine in incremental mode. Thus when the Z move is called in the G83 cycle the Z axis will decrease by -0.08, which is equivalent to going upwards by 0.08.

I'm not at all sure that using a G91 mode is permissible wit canned drill cycles.

Craig

Why is it using a G91 in canned cycle ?

Hi,
G91 means incremental mode and any ordinate (X or Y or Z etc) will move the nominated ordinate distance from the current location, not the absolute location
that you may be more familiar with.

If the controlled point is at X₀,Y₀ and a code:

G91 G81 X0.39370079 Y0.39370079 Z-0.08000 R0.05000 F3.0 is called then the machine will drill a hole
0.393" in X from X₀ and 0.393" in Y from Y₀

Note a later chunk of code:

N7 G91 G81 X0.39370079 Y3.60236221 Z-0.08000 R0.05000 F3.0
N8 X1.14173228 Y0.0000
N9 X0.000007 Y-3.20866142

This will drill three holes, the first 0.393" from X₀ and 3.6" from Y₀,
then another hole 1.14" from the current X and the same Y,
then another hole at the same X but -3.2" from the current Y.

So G91 is modal, that is it stays in incremental mode until it encounters a G90 and goes back to absolute mode. Likewise G81 is modal, any two X,Y coordinates will drill another new hole
at the nominated distances from its current location until a new motion mode is called.

In order for your drill cycle to drill downwards (in G91 mode) you need to change Z-0.08000 to Z0.08000.

Craig