The DRO uses an inexpensive digital dial indicator that’s held in place on the apron with powerful rare-earth magents. The stop clamps to the top of the cross-slide and presses against the indicator’s plunger, which measures the movement of the cutting bit.
This article describes how I added an easy-to-make DRO (Digital Readout) to the cross-slide of my 7×12 mini-lathe. It uses an inexpensive digital dial indicator that I bought from Harbor Freight for about $25. It works very well and you won’t have to drill any holes in your lathe or disassemble it to install it.
I’ve rarely seen a picture of a mini-lathe with a home-made DRO on it (or any kind of DRO), even though they seem to be fairly common on mini-mills. The ones for mills are usually made from inexpensive digital calipers or scales. I considered using them on the mini-lathe but rejected the idea because there is very little room to put them where they won’t be in the way. They will probably collect piles of swarf, the displays are also likely to be difficult to read and the buttons will probably be located where they will be awkward to push.
Using a digital dial indicator eliminates or minimizes those problems, although it is not a perfect solution. You’ll have to read the display and buttons upside down, which is not really much of a problem because they’re quite large and easy to read.
The indicator has a range of just 1-inch, but my design uses an adjustable bracket that will let you engage the DRO where ever you need it.
The DRO has two parts. The first is the indicator holder. It’s an aluminum bracket that attaches the dial indicator to the apron using very powerful rare-earth magnets. The magnets are located where they are unlikely to attract steel or iron chips. The second is a stop that clamps to the top of cross-slide and makes contact with the point of the indicator.
The stop can adjust two ways so it can always be made to press against the indicator’s probe, no matter the diameter of your work piece. You just slide it along the top of the cross-slide until it makes contact with the tip of the indicator, which is mounted on the apron. I thought there might be situations, like when working on a very large diameter workpiece, where the stop might not be able to contact the indicator. So I also added an adjustable rod to extend its reach. I now know it’s not needed, although it might if you adapt my design to another lathe.
The DRO does not interfere with the lathe’s controls and you can easily remove it in seconds if you want.
The DRO works very well and it has really improved my productivity. I no longer have to keep stopping to measure how much more metal I have to remove, or keep track of how much I’ve turned the cross-slide knob and then calculate how much more I need to cut.
Most of the time the DRO and the cross-slide dial are in complete agreement, or at least within five ten-thousandths (.0005), which is the resolution of the DI. When they disagree it’s usually because of backlash.
However, I was surprised to find that they would sometimes consistently disagree by forty-five thousandths, and it wasn’t due to backlash. I haven’t fully investigated the cause yet, but I’m pretty sure it’s going to turn out to be axial end play in the leadscrew. It’s a pretty common mini-lathe problem caused by a gap between the head of the leadscrew and the flange it is suppose to turn against. The most common fix is to make a small washer to fill that gap. It’s not really an issue and I’ve learned to trust the DRO.
This a prototype and not a finished design. I am hoping that others who are smarter and have better machining skills will think of ways to improve it and then share their ideas. That’s why there are no plans for it yet (a shortage of spare time and poor CAD skills also has something to do with it). So, until I get some plans drawn, I hope my photographs will allow you to make your own if you want to. Please let me know if you have any questions and I’ll do my best to answer them.
Continue reading A Homemade DRO for the 7x Mini-Lathe