A few years ago, I had a small machining project to do on my old manual lathe, and it seemed to me that it would be somewhat faster to do the work accurately if I added DROs (Digital Read Outs) to the lathe carriage and cross slide axes.

iGaging sells a line of DRO kits that while light on features, are reasonably accurate and very affordable. I bought a set and installed them on my lathe. They worked well for my project and I was satisfied with them.

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Since then however, Iíve begun really feeling the limitations of these budget instruments.

First, they run from coin cell batteries, and a couple of times now Iíve gone out to use the lathe to discover the batteries were dead and needed to be replaced.

Second, theyíre a bit laggy. There is about eight tenths of a second between a movement on the scales and the display showing that new position. Itís a little maddening for precision work since to hit a particular number, you have to really slowly sneak up to the number.

Third, the scales can only be set to read linear position. That makes a lot of sense for general purposes, but when mounted on the cross slide of a lathe that means itís displaying radius. Again, that makes perfect sense, but in practice Iím often trying to hit a specific diameter, and I end up having to take measurements and divide by two. Many higher end lathe DROs let you display the cross slide as radius or diameter. The whole point of DROs is to let the machinist work more quickly and more accurately, making fewer mistakes because the computer is doing the math for you.

Fourth, the preset function (where you set the position counter to a specific value) is very slow and cumbersome since there is no keypad. It reminds me of sending a text message on an old flip phone. In practice it was so awkward and slow that I never used it.

Poking around on Youtube, I found a video where someone had gotten an Arduino to read the output of a digital caliper, and I wondered if anyone had tried that with an iGaging DRO scale. A little searching found the really nice ďTouch DROĒ project, where Yuiri B. has documented how to talk to a few different types of iGaging scales.

My first thought was I have to try this myself. I got out a breadboard and a Teensy LC and after a little experimentation was indeed able to read the scales.

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Digging through my electronics parts box, I soldered up a board with two 7 segment 8 digit led displays, a pair of 4 character 14 segment LED displays for input feedback, a 4x6 button keypad, a pezio buzzer for audio feedback, and a shift register with 8 LEDs hooked up to it.

A little bit of software later, and I have a custom DIY DRO for my lathe.

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The keypad lets me toggle settings, like switching the display between imperial and metric, switching between radius and diameter display, absolute or incremental position display, and to allow easy numeric entry for presets.

There is still some lag. It takes 93 milliseconds to read both scales, but I suspect there is some internal smoothing going on inside the scale sensor and the best I can do is about a third second of lag. Thatís two and a half times better than what I had before, so Iím happy about that.

This ended up being two weekends of work, but I had a lot of fun doing it and now Iíve got a much more capable and responsive DRO.

John Knoll