...might try using a R value and discard the I K
G18 G3 X100. Z50. R.50

....If, machine home position for Z axis is zero and you use a gage block to set tool heights from Top of Part.... than all of the Offsets would be a negative number (my way its easier for me)...Big Shops use a Tool Setter.. programming a G43 and G44 would make a difference also, depending how You want to set your tools.