Arc motion in Z axis rapid

[BrandonH]

We have a late '90s Awea SP3016 bridge mill with a fanuc controller. For some reason the X and Y axis will start to move before the Z axis reaches its destination. The motion looks like an arc. If you turn the rapid rate down it is less pronounced, but at 100% it will actually catch a drill tip on the edge of a hole, for example, if you dont lift high enough. I understand some machines rapid differently, (dogleg vs. straight) but i thought, as a rule, Z had to reach its destination BEFORE X and Y moved? Is there a parameter for this? It sure would be nice if I didn't have to lift over an inch on my rapid moves.

 

Thanks.

[gcode]

Go through your machine. There should be a G?? which means "exact stop" which forces the Z to wait until

X and Y are on location

a quick google search came up with this

 

G60 unidirectional approach (rapid)

G61 Exact stop on (modal)

G64 exact stop off (modal)

 

but it will vary from machine to machine... or not be there at all if the machine builder didn't include it.

 

this could also be caused by mechanical issues with your lead screws and/or axis encoders

[BrandonH]

Thank-you. Looks like I need to do some checking.

[chris m]

G60 / G61 is typically only active in feed moves; with a Fanuc the machine should be in exact stop by default on rapid moves. Are you saying that your XY move and your Z move are on different lines, but the machine is moving simultaneously in all three axes?

 

C

[BrandonH]

Are you saying that your XY move and your Z move are on different lines, but the machine is moving simultaneously in all three axes?

 

Yes, but only in drill cycles. Sorry, I forgot to mention that.

It also does it with the "G08 P1" on and off.

 

( 17/32" DRILL | TOOL - 13 | DIA. OFF. - 105 | LEN. - 105 | TOOL DIA. - .53125 )

( K_US_STANDARD_TAP 5/8X11 - 5/8"-11_TAP - D DRILL )

N760 T13 M06

N770 G0 G90 X7.25 Y16.75 S348 M03

N780 G43 H105 Z1. M08 T32

N790 G08 P1

N800 G98 G83 Z-2.3471 R.125 Q.1594 F3.

N810 X0. Y16.

N820 X-7.25 Y16.75

N830 Y-16.75

N840 X0. Y-16.

N850 X7.25 Y-16.75

N860 G80

N870 M05

N880 M84

N890 G08 P0

N900 G91 G28 Z0. M09

N910 M01