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Digital Readout (DRO) Systems are used for indicating the position of the cutting tool relative to a workpiece. The positions are detected by encoders mounted on the axis. They feature a numeric display and keyboard. DRO systems are used with milling and boring machines, lathes and surface grinders.

Diagram of a DRO System

DRO System diagram

Encoder Defined:

Encoders are sensors that electronically collect data, including count, direction, position and speed. They are used with a glass linear scale to convert the encoding. The data is then sent to a machine, which in turn uses the information for the application required.


Measuring for a DRO

Overall length of the scale and the measuring length of the scale’s travel are very different. The overall length is the “footprint” space required. The measuring length indicates how much the scale can measure as it traverses the axes it is mounted on.

Take the following steps to measure the proper travel length for X, Y and Z axes. Use a tape measure to identify the amount of space you have to install an encoder. Then follow the steps below to determine the useful measuring length. Remember that the measuring length must be less than the hard stops of the machine to avoid damaging the encoder.


  • X-axis (right to left) measurements can be identified by moving the table to the furthest point on the left, marking a line between the table and stationary surface (saddle), then moving the table again to the far right. Measure from your mark to the right edge of the stationary surface.
  • Y-axis travel (in and out/front to back) measurements can be identified by moving the table to the furthest point forward, marking a line between the base of the machine and the stationary surface (saddle), then moving the table the furthest point back. Record that measurement.
  • Z-axis travel (up and down) measurements are the total distance traveled by the quill.
  • W-axis travel (up and down) measurements can be identified by moving the table to the lowest point, marking a line between the table and the stationary surface (saddle), then raising the table to its highest point. Record that measurement. Typically used with Knee Milling Machines
Measuring DRO System Video

Essential Tip:

Some DRO’s can also display a 4th axis on a knee mill. This would be the W-axis, which can be displayed separately or electronically, coupled with the quill for total Z-axis movement.


DRO Linear Scales are used for capturing information from the movement of the scale and converting the information into a digital signal, which is then transmitted by the encoder to the DRO. They are typically made of precision glass or are inductive or magnetic.

Glass scales are used in precision applications. They are resistant to changes in size, shape and density. The glass is designed to function where evenly spaced light passes through the glass, forming a pattern on a photoelectric sensor to generate signals to the DRO. They offer good protection from dirt and coolants, but are vulnerable to contamination. They are more economical than magnetic scales.

Inductive or Magnetic scales are durable, and resistant to coolants, liquids and dirt. They have a smaller cross-section than glass scales and are ideal for machines where space is limited. They measure changes in induced or magnetic energy. The energy differences are converted to electrical pulses read by the DRO. Magnetic scales can be cut to any length.

DRO System Image

DRO systems are commonly engineered to monitor multiple axes. The 2-axis DRO system can monitor X- and Y-axes. The 3-axis DRO system can monitor X-, Y- and Z-axes. The 4-axis DRO system can monitor X-, Y-, Z- and W-axes.

X-axis travel, also known as Longitudinal Travel, measures the maximum distance that the working surface moves in a right-to-left (horizontal) motion.

Y-axis travel, also known as Cross Travel, measures the maximum distance that the working surface moves in a forward-and-backward (in-and-out) motion.

Z-axis travel, also known as Quill Travel, measures the maximum distance that the quill can travel up and down.

W-axis travel, also known as Knee Travel, measures the maximum distance that the working surface moves in an up-and-down (vertical) motion. Typically used with Knee Milling Machines.

DRO Systems Image


DRO Equipment from MSC:

DRO Counters are used to display information collected by a scale and encoder. They can display their counts in inches, millimeters, degrees, or RPM units.

DRO Brackets & Mounting Hardware bracket kits, mounting arms, and pivot assemblies are available from MSC. Select the right accessory for your DRO System.