M-Series Operator’s Manual 4/9/15
G93 - Inverse Time
Rather than using a conventional federate in Inch per Minute or MM per Minute, F in inverse time mode specifies
the movement frequency for subsequent moves. Specifically, the inverse time feedrate is the inverse of the amount
of time that a move is allowed to take.
For example, using inverse time, the block:
G1 G93 X10 F1
takes 1 minute to cut, regardless of X length. At F2.0 (1/2.0 minute) it takes 30 seconds; At F3.0 it takes 20
seconds, and so on.
G93 is Modal, and remains in effect until a G94 is issued to cancel the G93.
Example of use in a program:
G0 G54 G90 X2.2126 Y-1.1995 A94.75 B-.161 S3000 M3 ; Move to start
G43 H26 Z7.0002 M8
Z3.1002
G1 G93 X2.2048 Y-1.2593 Z3.0204 F100. ; Enable Inverse Time
X2.2052 Y-1.2586 Z3.0202 A94.756 B-.162 F30000. ; 1/30000 min for move
X2.2079 Y-1.2578 Z3.0197 A94.763 B-.173 F30000. ; 1/30000 min for move
X2.2124 Y-1.2566 Z3.0189 A94.773 B-.189 F30000. ; 1/30000 min for move
X2.2184 Y-1.2551 Z3.0179 A94.786 B-.212 F24065.56 ; 1/24065 min for move
X2.2258 Y-1.2533 Z3.0167 A94.802 B-.24 F19736.14 ; 1/19736 min for move
X2.2345 Y-1.2512 Z3.0155 A94.819 B-.272 F17187.45 ; 1/17187 min for move
G93.1 – Velocity Scrubber for Smoothed Inverse Time Data
This special feedrate interpretation mode substitutes inverse time feedrates (usually posted from a CAD/CAM
program) with optimized feedrates to ensure that the tool tip center is moved at a set feedrate in physical 3D space,
taking into account tool length offset and the machine geometry as set by parameters 116-119 (see Chapter 14) .
The set feedrate (F) can be on the same G-code line as the G93.1 or can be the last modal feedrate specified on prior
G-code lines.
This mode is intended for CNC jobs run on machines configured with a triangular rotary 5th axis such as a Tilt
Table or Articulated Head (see parameter 166 in Chapter 14), although that is not an enforced definite requirement
to turn on this mode. It is recommended that moves programmed with this mode should be in small vectors, and
any long moves that require a sweep of a rotary axis by more than 10 degrees should be broken up into 2 or more
smaller moves. Note that Smoothing must also be turned on (P220 = 1) for this feature to work; otherwise, it will
be treated as a regular G93 (Inverse Time).
Example of use in a program (based on the example from G93 above):
G0 G54 G90 X2.2126 Y-1.1995 A94.75 B-.161 S3000 M3 ; Move to start
G43 H26 Z7.0002 M8
Z3.1002
G1 G93.1 X2.2048 Y-1.2593 Z3.0204 F150. ; Force tool tip to move 150 in/min
X2.2052 Y-1.2586 Z3.0202 A94.756 B-.162 F30000. ;Ignore F..Move at 150ipm
X2.2079 Y-1.2578 Z3.0197 A94.763 B-.173 F30000. ;Ignore F..Move at 150ipm
X2.2124 Y-1.2566 Z3.0189 A94.773 B-.189 F30000. ;Ignore F..Move at 150ipm
X2.2184 Y-1.2551 Z3.0179 A94.786 B-.212 F24065.56 ;Ignore F..Move at 150ipm
X2.2258 Y-1.2533 Z3.0167 A94.802 B-.24 F19736.14 ;Ignore F..Move at 150ipm
X2.2345 Y-1.2512 Z3.0155 A94.819 B-.272 F17187.45 ;Ignore F..Move at 150ipm
G94
-
Cancel Inverse Time
G94 is used to cancel Inverse Time feedrates, and return to regular Feed per Minute feedrates.
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