Mdi commands I'm confused

I set my machine to machine position x-304.000 y-210.000 z-3.000. I zeroed the machine to this point.
When you click on position it shows x0 y0 z83.750. Now I issue a /g90 then /g0y-5. The machine moves to -y-5.000 i machine coordinates. If I issue /g91 then g0y-5 it also goes to machine coordinates y-5. how does one get x or y to move 5 mm not go to machine coordinate -5.0? In answer to my previous question I found the quick action and jog command to move to WCS x0y0. This is what I was looking for in that question.

g90 and g91 are giving instructions of inches or metric. G90 is inch and G91 is metric. So that may be part of your problem that the internals of CC and CM uses metric and inch is converted. Using metric is slightly more precise because you can get rounding errors when using inch but it is thousands of an inch so most people cannot tell the difference.

The other issue may be about absolute positioning vs relative positioning. When you set X Y and Z zeros in CM you are offsetting from the home position. This is a relative positioning from home for your X Y and Z zeros. Not sure but when using absolute positioning it is based still on the home position and is constrained by the jogging limits from the configuration in CM.

I was under the impression that G90 and G91 absolute and relative and G20 and G21 were metric and imperial. So far I have found that if you issue the command G91 G0Y-5 The machine moves 5mm where as if you issue /G91 G0Y-5 it moves to absolute possition Y-5. G91 is supposed to be a modal command. Which I understand is supposed to be in effect until something changes that command like G90 or reset.

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You are correct. I gave advise that was not true. The g20 and g21 are about SAE vs metric. When you get old the brain works as first in first out so as I learn new stuff things like walking and talking are being pushed out the back.

Sorry for giving wrong advise.

When you use the slash “/” you’re telling CM to send the command directly to the machine.
CM internally uses G54 (workpiece coordinates) unless you specify G53 (machine coordinates)
so either try the G0Y-5.0 without the slash, or make sure a G54 is entered before that command.
Or you can include the G54 on that line G54 G90 G21 G0 Y-5.0

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All these years I thought that you had to use the / when using the MDI interface. So this must mean that the modal commands are handled by carbide motion not the controller. This answers a lot of my questions. I found the quick action and jog tabs that will move the router to my work X0Y0. But was having a lot of trouble to move the router a few MM from work zero. It kept moving the router to machine location when I sent G0Y-5.


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