Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 389)

Axis Motion
Chapter 14
14-13
In incremental mode (G91) the rotary axis is programmed to move an
angular distance (not to a specified angle as in absolute). The maximum
incremental departure depends on the programming format selected in
AMP by the system installer. The sign of the angle determines the
direction the rotary axis will rotate. For example if the current C axis
position is 25 degrees and the following block is programmed:
G91C50;
the C axis would rotate 50 degrees in the positive direction. The new C
axis position would be 75 degrees. If the current C axis position is 25
degrees and the following block is programmed:
G91C-50;
the C axis would rotate 50 degrees in the negative direction. The new C
axis position would be 335 degrees.
In incremental mode (G91), programming a value greater than the rollover
amount results in the rotary axis making one or more complete revolutions.
In absolute mode (G90), you cannot program a rotary axis move greater
than the rollover amount.
In circular interpolation mode (G02 or G03), you cannot program a rotary
axis move unless these conditions are met:
the rotary axis cannot be in the active plane
the rotary axis must be programmed in the same block as a valid circular
move made with the axes in the active plane
Important: The largest move that may be programmed with a rotary axis
is equal to the rollover amount,. Any attempt to program a move that will
generate more motion than the rollover amount, will be truncated and
moved to the position that has the same numerical endpoint as the
programmed position. For example if the following incremental move is
programmed from a position of 10 degrees:
G91C370;
the actual endpoint of the above move will still be 20 degrees; however,
the rotary axis will not get there by revolving one revolution. Instead, it
will position itself directly to 20 degrees without passing 20 once, as would
be expected.