Making an Inexpensive DRO

[Andrew] wanted a digital readout (DRO) for his mini lathe and mini mill, but found that buying even one DRO cost as much as either of his machines. The solution? You guessed it, he built his own for cheap, using inexpensive digital calipers purchased off eBay.

The DRO he created features a touch screen with a menu system running on an LPCXpresso, while smaller OLED screens serve as labels for the 7-segment displays to the right. The DRO switches back and forth between the lathe and mill, and while the software isn’t done, [Andrew] hopes to be able to transfer measurements from one machine to the other.

In a very sweet touch, [Andrew] hacked cheap digital calipers to provide measurements for each axis, where they provide a resolution of 0.01mm. There are six daughter boards, one for each caliper, and each has a PIC that converts from serial to I2C, freeing the main firmware from dealing with six separate data streams.

The DRO doesn’t have a case, [Andrew] has it positioned out of chip-range from either machine.

A previous DRO we featured in 2012 used an Android tablet as its display.

17 thoughts on “Making an Inexpensive DRO

  1. This is a great project and something I was considering for my mill. A casual search of Aliexpress though shows a 3 axis DRO accurate to 1um is less than $250 delivered.

      1. True, and these may be OK for most. The ones I quote are optical and include the read out box itself (and all the functions you would expect) + armored cable etc. I decided to go with the ‘pro’ ones simply for the superior accuracy.

  2. nice project but i disagree with dro’s are expensive. look around i know more shops that have tossed out, yes tossed out very nice dro’s with glass scales that are infinitely more accurate than what he has made because they were upgrading and could not get anyone to stop by and take the parts. again nice project but the premise that dro’s are expensive is just wrong unless you are only willing to purchase new.

  3. Check out http://www.yuriystoys.com/?m=1
    He makes some little boards that interface to crappy caliper scales or good quadrature encoders and connects to a android tablet over Bluetooth. I bought one for work and it works great. If my anilam ever dies on my lathe I will replace it with one of these boards and an old tablet.

  4. A few years back, I built the “Shumatech” DRO. Looks very good, like a finished product, but it was an AVR based DIY project that used either quadrature scales, or cheap Chinese scales. I like the build quality… The guy had screen printed self adhesive overlays printed, so all the tactile switches would have nicely labeled buttons and everything. I don’t think the kits are still in production. China finally caught up can came out with cheap DROs themselves… Still, the Shumatech DRO was really nicely featured, and you had the joy of knowing you built it yourself!

  5. “OLED screens serve as labels”…..
    Hmmm… When a felt tipped marker is an option, we need electronics and software?

    I _love_ when people do things because they can, bonus points for sharing a write up. Learning, experimenting and trying are awesome – just stop holding it up as a “great alternative to an existing product”.

    1. Never used this so just spitballing here. Using screens as labels you could rearrange the readouts and compare measurements from any given axis on one machine, while you work on your piece on the other.

  6. There are purpose made DRO versions of the caliper scales available in various lengths. This is one example chosen simply because I knew where to find it.

    http://www.grizzly.com/products/Absolute-Digital-Read-Out-24-/T26541?utm_campaign=zPage&utm_source=grizzly.com

    Glass scales have better temperature coefficients, but remember that the workpiece expanding when you cut it is a much larger source of error. It would not be hard to switch out the supplied readout with an MCU that applied a temperature correction for the steel scales.

    Hacking calipers only makes sense if you can live with 6-12″ scales.

    1. The wixey table saw digital readout tapes are highly accessible too, they come in long lengths, and can be read with standard cheap caliper heads. I made a dro up using wixey tape and caliper heads inside machined delrin housings that hooked up to a now very outdated yadro running on a old pc. Now you would use one of the arduino or yuriy’s dro to read the scales but the fabrication of the scale is still unchanged.
      Having said that, caliper head dro’s are unreliable in my experience and they don’t like coolant or chips, I’ve since replaced my homebrew one on the mill with a sinpo unit with glass scales from a chinese vendor. I’ve managed to break a glass scale in a bad crash but it broke the scale head housing rather than the glass inside, I bought just a replacement head alone and rebuilt my scale with it.
      Next build experiment is hooking glass scales up to yuriy’s dro as posted by someone else, since I now have a spare scale after a ebay snipe, and I have no dro on my surface grinder.

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