You really don’t need any calipers at all to measure your Touch Plate. You can use your CNC Machine to do it for you. Here’s how:
Step 1: Load Universal G-Code Sender or PicSender
Step 2: Place your Touch plate upside down on your machine with the wires connected to the touch plate and spindle. Make sure that the touch plate X and Y axis are aligned as square as possible to the machine
Step 3: Jog your bit so that it is almost touching the touch plate on the X axis on the right side and then slide the touch plate over so that it is actually touching the bit.
Step 4: Without moving the touch plate, raise the Z axis up so that the bottom of the bit is just above the touch plate milled out portion but not above the milled out edges.
Step 5: Type these commands in the command line of your G-Code Sender and hit enter for each command: “G92 X0”. This will set your X axis position to zero. Then this command: “G38.2 X-2.5 F5”. The X Axis will move left until it touches the milled out edge of the touch plate and then stop. Look at your work position coordinates in your G-Code sender and it will show you how far it traveled in the negative direction. Drop the negative symbol and you will have the exact measurement of the X Axis.
Step 6: Repeat all the above for the Y axis and replace the letter X with the letter Y in the commands to get your Y axis measurement.
Step 7: For the Z Axis, with the touch plate right side up placed in a normal location so that the milled out area is flat against the material surface, position the bit above the touch plate and enter the following commands hitting enter after each one: “G92 Z0” then “G38.2 Z1 F3” then “G91 G0 Z0.1” then “G92 Z0.1”. This will set your Z axis at the top of your block and then raise it up 0.1 inches then set the work position at 0.1 inches.
Step 8: Carefully remove the touch plate and wires. Jog your Z axis down until it touches the surface that the touch plate was sitting on. Use a slip of paper under the bit and jog down until it is trapped tight enough that you can barely slide it out without tearing but it is impossible to slide it back under the bit. A piece of candy wrapper works well for this. Now read your Z position and you will have your Z Axis measurement.
And you thought CNC Machines were only for carving!!