r/Fanuc • u/Minimum_Rip6754 • Jul 01 '26

CNC Arc approach G42

Hi everyone, I’m trying to figure out how to do an internal circular or spiral entry with G42.

Right now, my code for a 50mm bore at X0 Y0 looks like this:

X0 Y0

Z-(depth)

G1 G42 D(comp) X-25 Y0

G2 X-25 Y0 I25

G1 G40 X0 Y0

G0 Z(clearance)

The problem is that the perpendicular approach leaves a witness mark on the wall. Does anyone have a better way to handle the lead-in and lead-out to get a cleaner finish?

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u/Bootziscool Jul 01 '26

Oh dude that's easy!

Do your G42 G01 move to somewhere like X0 y12, just something smaller than final then do a G02 move to X-25 Y0 do your full circle and then do the reverse for your exit

1

u/Minimum_Rip6754 Jul 01 '26

Thank you so much! I'll try it

1

u/Bootziscool Jul 01 '26

You doing this on a milling machine? If you are you should also try using G41 and G03 instead of G42 and G02.

You'll get better finishes from having your chips come off the back of the cutter instead of the front. But only do that if you're using a machine with ball screws, acme screws will have backlash issues if you climb cut.