In my opinion, no milling machine should be without a digital readout (DRO). If you ever had to use an old machine without a DRO, you would be amazed that anyone could produce good results. Counting turns of the handle, reading tiny numbers on dials, making sure all movements were from the same direction, and having to compensate for lead-screw wear; none of this is necessary if the machine has a DRO.
There several different technologies used to build the linear scale used to determine machine position. The DRO on our mill uses high precision glass scales. Inside the scale housing (spar) is a long strip of glass. The glass was coated with a fine layer of chromium, then fine lines were etched in the chrome as many as 50 per mm. The reader module, which is attached to the spar, slides along the glass scale. The circuitry inside the reader module shines light through the glass scale and using a pair of light sensitive detectors can “read” the glass scale and output pulses to the display unit. The display unit counts the pulses to determine location. The small computer within the display unit can provide many different ways to use the position data. These functions are beyond the scope of this blog.
The machine should be ready for installing in The MakerBarn sometime this next week. Look for upcoming classes in machine operation and certification.