DIY Tachometer for Your Mill or Lathe

One of the new features in the upcoming version of TouchDRO app is tachometer readout. The beta version of the application had full tachometer support for some time now. Over the last few weeks I added directional tachometer support to all four controllers. In this post I will try to give you some ideas on how to build a tachometer for your mill or lathe using commonly available parts. Your setup will vary, of course, but the main principle will be the same, so you shouldn't have too much trouble to adapt these designs to your particular needs.

Android DRO Step By Step Overview

Since I added a DRO to my mill I can't imagine how I lived without one for so long; it makes working on the mill so much easier and more efficie. Since you're reading this post, you are probably looking into building a DRO as well, and if you feel lost, you're not alone. Although I've been trying hard to keep the project as simple as possible, so it remain accessible to people with little or no experience with electronics or computers, it might seem a bit overwhelming.I this post I will provide a quick summary of the steps needed to get a DRO up and running with links to more information where appropriate.

TouchDRO Initial Setup

TouchDRO is designed to work with a wide range of scales and machines, but it will not work right out of the box. After the application is installed, it needs to configured to match your particular setup. The process isn’t complicated and takes just a few minutes, though.

By default the application is configured for a three-axis vertical milling machine that uses imperial units. If that matches your setup, the only thing you’ll need to do is to configure your scales and the DRO will be good to go. Otherwise, there are a few additional settings that needs to be changed.

DRO Scale Calibration

I’ve received a fair number of complaints about the readout being inaccurate when the default counts-per-inch were used. These problem can be caused by several different issues. First of all, CPI for most of the the capacitive scales isn’t officially provided by the scale manufacturers. The values for many of the commonly available scales have been found experimentally, and might be off by one or two counts. In addition, there are manufacturing tolerances, rounding issues etc, that can skew the numbers even more. Furthermore, many of the scales that come from China are metric. For instance, the glass scales that are advertised to have resolution of 0.0002” have resolution of 0.005mm, and 5 microns don’t equal 2 ten thousands. This leads to an error in CPI. Based on the 0.0002” resolution the CPI should be 5000, but in fact it’s 5080, which is almost 2% off.

More New Features in TouchDRO

About a week ago I started posting nightly builds of the new release of TouchDRO application. Based on the feedback provided by the beta-testers I've made a few changes to the user interface. The biggest one is the addition of the new "Axis Details" screen. It's purpose is to display the feed rate and chip load while the axis is moving, and offer few axis-specific functions.

Clicking the axis readout brings up the "Axis Details" view

Beta Version of TouchDRO Now Available

Yesterday I published the first beta build of the TouchDRO application to the Google Play Store. This release includes a few major upgrades, such as tool library, tachometer, configurable user interface and preference banks. Tachometer output is pretty much self-explanatory; the other three need a bit more clarification.

Battery Backup For DRO Interface

In the first part of the build instructions for the MSP430G2 LaunchPad-based DRO controller I showed a few pictures of the unit I built for my mini mill. Out of necessity my controller had to have battery backup, since the power in my garage was very flaky and the circuit breaker tripped every time I looked at it crooked. The battery backup circuit I built originally was a quick stop-gap measure that would get me through until the garage was rewired properly. I didn't spend much time designing that circuit. Since several people asked me to provide more details about it, I decided to take a more methodical approach for this post.

TouchDRO Coordinate System

DRO Coordinate System

One of the aspects of the TouchDRO application that causes confusion is the coordinate system. Every once in a while I get questions like “Can I do hole circle/pattern/tool offset on a different plane because on my mill the spindle is X (or Y) axis?”, or something along these lines. This question really means that the DRO is not set up right and the user is trying to compensate for it by “customizing” the user interface. Obviously, this is your DRO and you are free to set it up whichever way you like it. TouchDRO is pretty flexible, and the basic DRO functionality will work just fine even if you have axes mixed up and backwards. After a while you will likely get accustomed to it, and use the DRO without second thoughts. Never the less following the conventions is a good idea in the long term.