18i Lookahead during G68 3D

[mossj237]

Hi,

I'm really struggling with a control programming problem. We have an 18iMB with all the bells and whistles. The machine is a large bridge mill with a right angle head. With it we can do "five sided machining." The way we write programs for this machine is we use a G120 line that is a custom code provided by the machine manufacturer (won't be able to find it in the general Fanuc manuals.) Within this code however, the machine uses G68 3D. The problem that we're having is that we're unable to get any of the high speed or high precision lookahead functions to work. The result is very choppy movement during circles, etc. The machine will periodically hesitate. All we want to do is smooth this out.

Is there a default lookahead value that we can adjust?

Question: How can we smooth out our machine's motion while in G68 3D and feeding at a high feed rate?

Any help would be greatly appreciated. I seem to have run out of other options.

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[Dan Fritz]

Isn't G68 used for coordinate rotation? My manual says that G08, G05, and G05.1 are used for high speed look-ahead. Here's are two clips from the manual:
-----------------------------------
G05.1 Q_ ;

Q1 : Start simple high–precision contour control mode
Q0 : End simple high–precision contour control mode

A block for specifying G05.1 must not contain any other command.
Simple high–precision contour control mode can also be canceled by a
reset.

-----------------------------------
G08 P_;

P1 : Turn on look–ahead control mode.
P0 : Turn off look–ahead control mode.

[mossj237]

Isn't G68 used for coordinate rotation? My manual says that G08, G05, and G05.1 are used for high speed look-ahead. Here's are two clips from the manual:
-----------------------------------
G05.1 Q_ ;

Q1 : Start simple high–precision contour control mode
Q0 : End simple high–precision contour control mode

A block for specifying G05.1 must not contain any other command.
Simple high–precision contour control mode can also be canceled by a
reset.

-----------------------------------
G08 P_;

P1 : Turn on look–ahead control mode.
P0 : Turn off look–ahead control mode.

Dan,

Thank you so much. I searched that book over and over again, but I skipped over "Advanced Preview" because I just didn't know what that meant. I was looking for "High Speed" something or "lookahead" etc.

I found the G05.1 a while ago, but it will not work in the coordinate rotation. G08 worked!! If you read the acceptable codes in the manual, it even says that it'll work!

You made my day.

Thanks again,

Jeff