How to switch from diameter positioning to radius positioning and vice versa on a lathe

On a lathe where X-axis values can be output either in diameter or radius mode, the following commands can make the switch possible.

  • MODE/DIAMET: selects diameter output for the X-axis, if supported on the machine
  • MODE/RADIUS: selects radius output for the X-axis, if supported on the machine

The macro variable $XDIAM tracks the radius vs. diameter state of the X-axis output.

  • This variable can be modified to change the representation mode of diameter vs. radius X-axis values
  • The default state of this variable is the same as the default starting mode as defined in QUEST
  • Set this variable to $FALSE for radius output and $TRUE for diameter output
  • But using the variable to set the mode will not output the corresponding X-axis diameter / radius NC codes, unlike the MODE command

Benefit to user

  • Helps the user to switch the X-axis output from diameter to radius or vice versa on a lathe machine
  • One specific application is on a turn-mill machine where the X-axis values need to be in diameter mode for turning operations and in radius mode for milling operations

For more information or comments, please do not hesitate to contact Phil at