Digital Read Outs

Digital Read Outs (DROs) can refer to any of the various types of digital numeric displays used on measuring tools, tachometers, etc.

However, as the term is used here, I’m referring to precision scales with a slider, much like a digital caliper, that are designed to be mounted on machine tools, such as a lathe or mill, to precisely indicate the position of the work relative to the cutting tool.

Various DRO styles & sizes

On a lathe, they are typically mounted along the bed and cross-slide, so you need only two readouts. On a mill, you typically would have readouts for the X, Y and Z axes, but can get by with just Y and Z for many operations.

DROS are available from many sources, including the usual machine tool suppliers such as Enco and J&L, but the ones they sell are for full-size industrial milling machines.

For the mini mill and mini lathe, LittleMachineShop.com, has some that are the right size. I got mine on eBay, from one or more of the eBay stores that sell industrial products (search for “DRO” or “Quill Kit”).

There are two basic designs for the DRO: horizontal and vertical, as seen in the photo above. The vertical style is typically attached to the quill of a milling machine, hence the term “Quill Kit”.

While both types have a built-in digital display, when it comes time to mount them on the lathe or mill, the display often ends up in a location where it cannot readily be seen - such as under the mill table.

Therefore, it is generally necessary to use these slides in conjunction with an external 2 or 3 axis display, sold separately.

Fortunately, all of the DROs I have seen, including the low-cost HF digital caliper, include a data port for feeding the readout to an external display.

In fact, some displays also provide DC power to the DRO through this port, obviating the need for a battery in the DRO. This is handy, since the DRO may end up mounted in a location where it is not readily accessible to change the battery.

Unfortunately, the design of the connector in the horizontal DROs does not do a good job of securing the data cable, so some extra rigging is usually needed to keep the cable from working loose from the data port.

Data port for external display