Super Cheap Super Simple DRO

If you have an old manual lathe, mill, or even a drill press, a digital readout (DRO) is a very handy tool to have. A DRO gives you a readout of how far you’ve cut, milled, or drilled into a piece of work without having to stoop to caveman levels and look down at a dial. Here’s a stupidly cheap DRO for all your machine tools. It should only cost five bucks or so, and if you need it, you already have the tools to manufacture it.

This build is inspired by an earlier build using the same single component – a digital tread depth gauge. This digital tread depth gauge is commonly found in countries that don’t use the US penny as currency to measure the depth of tread on a tire. The throw isn’t that large – only about 27mm – but with a few modifications it can fit on any machine tool.

The modifications include a small bit of metal glued to the back and four tiny neodymium magnets.  For the ‘tool head’ of this DRO, only a tiny plastic collar and another deo magnet are needed.

This digital tire depth gauge looks like – and probably is – the same mechanism found in those super cheap calipers from the far east. In theory, it should be possible to extend this modification to those digital calipers, making for a simple DRO with a much larger throw.

Thanks [Ben] for sending this one in.

15 thoughts on “Super Cheap Super Simple DRO

  1. Longer (6-24″) versions made for the purpose are readily available and quite cheap (e.g. < ~$50 ). Or for $10 you can modify a 6" caliper. It's hard to see a use for such a short range. For 1", a dial indicator is the typical solution and an extremely common novice's project.

      1. I don’t mean to be rude, but have you actually ever run a manual lathe or mill? If what you said were true people wouldn’t spend the money they do on professional DROs. After all they already have a slew of dial indicators. I’ve got indicators that read to 0.0001″ but they only have range of 0.25″. The only thing I use them for is checking runout and end play.

        BTW The use of magnets to hold the DRO in place is very foolish as it’s not likely to hold position reliably.

        1. I run several machines, Cylindrical grinders and the likes making tool’s for other machines. Something like this would be rather helpful. A lot of the work I do is machining carbide often to a really fine tolerance. Many of our tools measurement devices and even some of the mounts are held in place by magnets and we have never had an issue.
          Making engraving tools that have a V cut in to the tip that is smaller than a human hair and having to use a microscope that again is attached to the machine using a magnet works well for us.

          If the machine or work is vibrating enough to cause the magnets to move then there is likely some other more serious problems that are going to appear.

  2. It’s also possible to interface directly with many of the calipers. This allows you to display the numbers on a larger screen, add external buttons, foot pedals, and add advanced functions. Here’s some Arduino-compatible code I wrote based on the Digimatic protocol that Mititoyo uses (others are likely similar):

  3. A quick check of ebay shows you can get the devices for ~$5 delivered. I think he used his hi tech toys because he had them but you could just as easy hot melt glue the magnet on the end of the rod and you could make the base with a jig or a band saw and a drill with bits. I suspect the magnets are not the best for accuracy, but given the stuff I make, I think they would be fine. I am not NASA here. The 25mm throw is more of an issue, but I can see this idea being expanded to the 6 or 12″ calipers that places like HF sell on the cheap. Overall an interesting idea.

  4. Some times ago, I did think about a similar feature for reprap.
    Maybe it would be possible to attach a modified calliper for all three axes in order the machine to do autocalibration before printing.

  5. Or, take the wixey saw dro tape replacement part, machine a slot into a length of aluminium profile to embed it in, and fit a cheap caliper read head to it in a delrin housing and voila 1m long super budget dro.
    I still use the dials on my lathe though. I’ve got a rather effective micrometer bed stop I can use to do this sort of thing and having a digital read out doesnt make it one bit more accurate or give it new functionality. The self built saw tape dro was for a manual milling machine which was, as it means you can machine to co-ordinates off a drawing easier.

  6. Hello! i was on holiday when this got reposted! So to adrees the points, yes.. these are definitely using the same internals as cheap calipers. The magnets are really good.. 4 8mm neodynium magnets on the base give a much stronger magnetic force than the standard dti mag bases (but they can move the magnet on and off to make removal easier) Yep.. it’s a short through.. but I tend to use the dials to get close and use this for the last bit as was said. I’d love to pick up the wixey saw dro and tape/track kit but they are lots more money in the UK and boarder on the cheap end of of budget DRO setup. Finally… yes.. I used my CNC router to make the base.. cos I have one I out together! You could indeed glue some magnets onto the base and it would work as well! I have another tread gauge to convert and I think I might be able to extend the travel a little (maybe another 10mm or so).

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