Hackaday Prize Entry: Mini DRO For A Lathe

A manual lathe has dial wheels to control the feed of the main carriage and the cross slide to help take cuts on the workpiece. These feed wheels always have some backlash and require frequent resetting of the “zero”. The usual process would be to take measurements on the workpiece with either a vernier caliper or a micrometer at intervals which requires stopping the machine, adding up to increased machine time. The addition of a digital readout not only simplifies the process, but also reduces machining time substantially. Since the DRO magnetic strips are directly attached to the cross slide, the effects of backlash are mitigated.

[Igor] has just such a manual lathe and built his own mini DRO unit from scratch a couple of years back. Most DRO’s have encoder strips and sensors attached to the cross slide with a larger display unit attached separately on a stalk, with wires running between the two. [Igor] kept things simple by building a unit that fit within the space constraints he had. His unit consists of just two sensor modules – each attached directly to the slide. The main unit houses a linear hall sensor, electronics, buttons, a small LCD and batteries. The second axis unit houses just the sensor with a cable connecting it to the main unit for data and power. At the heart of the system is a pair of NSE-5310 linear hall sensor encoder chips. These work in conjunction with multipole magnetic strips. The encoder provides a 12-bit output, and the magnetic strips have poles spaced 2 mm apart. This translates to a theoretical resolution of almost 0.5 microns, but of course, the machine mechanics limit the actual results. The encoder chips talk to an ATtiny2313 over the I2C bus. Three buttons and the power supply round-up the hardware. To run it off a single 1.5 V rechargeable battery, [Igor] used a boost converter to get 3.3 V. The 5 V needed for the LCD is obtained by a voltage doubler connected to a PWM output from the microcontroller and regulated by a Zener diode. The second sensor unit connects via a TRRS 3.5 mm socket.

He added a Bluetooth module as an after thought, but ran out of GPIO pins as well as program space and had to get creative to make it work. The plan was to transmit the data to an Android tablet which would work as a large, remote, wireless display. He never did use that feature though, being satisfied with the small LCD display. There’s several things that went wrong in the build, and if he were to replicate the project again, several changes and improvements would help. So if anyone plans on doing something similar, do check up [Igor]’s project logs first.

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.

Digital Caliper Sacrificed For DRO Project

In general, machining metal on a lathe or mill takes skill and patience as the accuracy of the cuts are important. To make those accurate cuts, it is important to know where the tool is located and how far it moves. For manual machines, the most basic method of determining position is by using graduated dials mounted on the hand cranks. Although these graduated dials can certainly be accurate, they may be difficult to see and they also require the operator to do math in their head on the fly with every full revolution of the dial. Another option would be a digital read out (DRO) which has an encoder mounted to the moving axes of the machine. This setup displays the exact position of the tool on an easy to read numeric display.

Professional DRO kits for mills and lathes can cost between a few hundred dollars to several thousand dollars.  [Robert] has a lathe, wanted a DRO but didn’t want to shell out serious cash to get it. He built his own for super cheap in an extremely resourceful way…. using a Harbor Freight Digital Caliper. A housing was first fabricated so that the added equipment would not hinder the axis travel of the lathe. The caliper was then cut to length, installed in the housing and the entire assembly was then mounted to the lathe.

DIY Lathe DROIt is totally reasonable to use the stock caliper display to read the positional information, however, even these cheap digital calipers have connections for the encoder output data, which can easily be read by a microcontroller. That means it is super simple to hook these low-cost digital calipers up to a display remotely located in a more convenient position.


Adding digital readout to a non-CNC mill

In the quest to add a digital readout to his mill, [Yuriy] has done a lot of homework. He’s sourced a trio of very capable scales, researched what kind of hardware his DRO should be based on, and even built a very cool display using seven-segment LEDs. After nearly a year of work, [Yuriy] finally hit upon something that works well: an Arduino and an Android tablet, perfectly matched for one of the prettiest machine shop displays we’ve ever seen.

[Yuriy] based his build off a trio of digital scales he bought from Grizzly. These scales bolt on to the frame of his mill and send data to their own display. An Arduino was used to pull the data off these scales and sent via Bluetooth to a Nexus 7 Android tablet.

Considering a DRO solely based on an Arduino and a character LCD would look a little chintzy – and the fact Arduinos can’t do floating point arithmetic – we’re really impressed with [Yuriy]’s very elegant solution.

Thanks [Lee] for sending this one in.