Cutter compensation is a feature of CNC machines that allows the programmer to specify the desired part geometry without considering the size and shape of the cutting tool. This simplifies the programming process and reduces the number of calculations required. Cutter compensation also enables the machine to automatically adjust the tool path to compensate for tool wear or changes in tool diameter.
There are two types of cutter compensation: G41 and G42. G41 is cutter compensation left, which means the tool is offset to the left of the programmed path. G42 is cutter compensation right, which means the tool is offset to the right of the programmed path. The direction of the offset depends on the direction of the tool motion and the coordinate system used.
Usage Format
The general format for using G41/G42 is:
G41/G42 D~ P~
where:
G41/G42is the cutter compensation code, either left or right.D~is the tool number that corresponds to the tool diameter in the tool table. This parameter is optional and can be omitted if the tool diameter is zero or the same as the previous tool.P~is the lead-in distance, which is the distance from the start of the compensation to the first point of the programmed path. This parameter is optional and can be omitted if the lead-in distance is zero.
Explanation
When using G41/G42, the programmer must ensure that the tool is positioned at a safe distance from the part before activating the compensation. This is done by using a lead-in move, which is a straight or arc motion that brings the tool to the start of the compensation. The lead-in distance should be equal to or greater than the tool radius, to avoid gouging the part or causing an alarm.
The programmer must also ensure that the tool is positioned at a safe distance from the part after deactivating the compensation. This is done by using a lead-out move, which is a straight or arc motion that takes the tool away from the end of the compensation. The lead-out distance should be equal to or greater than the tool radius, to avoid cutting into the part or causing an alarm.
The programmer must also use a G40 code to cancel the cutter compensation after the last cut. This will restore the tool to the programmed path and prevent any unwanted offsets.
Example
The following is an example of a CNC program that uses G41/G42 to cut a rectangular pocket with rounded corners. The dimensions of the pocket are 100 mm x 50 mm, and the radius of the corners is 10 mm. The tool used is a 10 mm end mill with a tool number of 1. The coordinate system is G54, and the spindle speed and feed rate are 1000 rpm and 200 mm/min, respectively.
% (Program start)
O0001 (Program number)
G54 (Select coordinate system)
G90 (Select absolute mode)
G00 X0 Y0 Z50 (Rapid move to initial position)
S1000 M03 (Start spindle clockwise at 1000 rpm)
G00 Z5 (Rapid move to clearance plane)
G41 D1 P10 (Activate cutter compensation left with tool 1 and lead-in 10)
G01 X-60 Y-35 Z-10 F200 (Linear move to start of pocket with feed rate 200)
G03 X-50 Y-25 R10 (Clockwise arc move to first corner with radius 10)
G01 X50 (Linear move to second corner)
G03 X60 Y-15 R10 (Clockwise arc move to third corner with radius 10)
G01 Y15 (Linear move to fourth corner)
G03 X50 Y25 R10 (Clockwise arc move to fifth corner with radius 10)
G01 X-50 (Linear move to sixth corner)
G03 X-60 Y35 R10 (Clockwise arc move to seventh corner with radius 10)
G01 Y-25 (Linear move to eighth corner)
G03 X-50 Y-35 R10 (Clockwise arc move to first corner with radius 10)
G40 (Cancel cutter compensation)
G00 Z5 (Rapid move to clearance plane)
G00 X0 Y0 (Rapid move to initial position)
M05 (Stop spindle)
M30 (Program end)
% (Program end)
The following text diagram shows the tool path and the cutter compensation for the example program. The dashed line represents the programmed path, and the solid line represents the actual tool path. The arrows indicate the direction of the tool motion and the cutter compensation.
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+----+-----------------+--+-----------------+----> X
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|<---- 100 mm --->|
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|<- 10 mm ->|
|<---- 50 mm --->|