Cutter Compensation

Cutter compensation makes the control drive the tool edge along the line in the program rather than the tool centre. The programmer writes the finished shape; the control offsets by the tool’s radius.

The practical consequence is the one setters care about: a wall that is out by a few hundredths is corrected in the tool table, not in the program.

Turning it on

Code	Does
G41	compensate to the left of the direction of travel
G42	compensate to the right
G40	off

D selects which tool’s radius to use: D2 uses the radius in row 2 of the tool table.

G41 D2 X10. Y0. F400.     (turn it on while moving into the cut)
...
G40 X-20.                 (turn it off on the way out)

Compensation is established and cancelled on a move, not on a line of its own. The move that turns it on is the lead-in, and it must be longer than the tool radius. Otherwise the control is asked to step sideways further than the move itself goes.

Probing moves are refused while compensation is on. Cancel with G40 first.

Correcting a wall

The radius the control uses is R.Geom plus R.Wear from the tool table. R.Geom is the tool as measured; R.Wear is where a correction belongs.

A wall left 0.04 too thick, cutting down one side:

• The tool is cutting 0.04 short of where it should. Take 0.04 off R.Wear and run the pass again.

Across a slot or a pocket, both walls move, so the width changes by twice what you change:

• A pocket 0.10 undersize needs R.Wear reduced by 0.05.

Use +INPUT on the offset screen so you are adjusting what is there rather than retyping it.

3D compensation

G41.2 and G42.2 compensate in three dimensions, against a surface normal the CAM system supplies with the move. It is not something you switch on at the panel, and it is a different subject from the G41 / G42 above. See 5-Axis Programs.

What compensation does not do

• It does not fix a wrong tool. If a 10 mm cutter is measured as 12, the geometry is wrong; correct R.Geom, not the wear.
• It does not remove the need for a lead-in. A shape entered directly at a corner will not compensate cleanly however the offsets are set.
• It does not survive a reset. Compensation is cancelled with the rest of the modal state; see Start, Feed Hold & Reset.

Where to go next

• Tool & Work Offsets: the table D reads from, and tool length compensation (G43, H).
• G & M Code List: the full set of compensation codes.