As you probably know, current model CNC machines can be used with two measurement systems – the Imperial (inch) measurement system and the Metric (millimeters) measurement system. A parameter setting controls which measurement system is automatically selected at the machine’s power-up, meaning you can have the machine default to your measurement system of choice.
The parameter that controls the current (and initialized) measurement system can be found on the setting page and can be modified without activating the parameter write enable (pwe) function. You need only be in the manual data input (MDI) mode to change this setting.
There could be a second, little known, parameter that is related to your measurement system choice. It determines what happens when you switch measurement systems. This parameter controls whether a true conversion of all data will take place (this is the desired setting) or whether the decimal point for all values will simply shift one place. If available, you’ll find documentation about this parameter in the measurement system selection section of your Fanuc Operators manual.
Again, the desired setting causes a true conversion of all numeric data, including position displays, tool offsets, and fixture offsets. On the position display page, for example, say a value of 10.0000 inches is currently shown for the X axis. When you switch to the Metric mode (by setting parameter or by commanding a G21), the X position display should be updated to 254.000 mm. If instead, it shows a value of 100.000 millimeters, the decimal point is simply being shifted one place to the right.
The true conversion is especially important if you’ll be running jobs in both measurement systems. When you go from job to job, it is likely that at least some of the tooling from the previous job will be used in the next job – after the measurement system change. Having the control convert all values between the measurement systems is important. It will keep the setup person from having to re-measure tools used in the previous job
