I bet you never thought you’d read THAT statement!
If you don’t know what a “DRO” is, then you must have REALLY not expected to read it.
A DRO, or Digital ReadOut, is a measurement tool and a display that attaches to each axis of a milling machine or metal lathe and clearly shows the distance traveled during milling operations.
The alternative to a DRO is to count the number of turns and markers on the hand wheel as you make your cuts, but I’m not a very good counter and longer cuts require a lot of turning the wheel (10 turns per inch on my machine). There is very little dispute around the assertion that you should use a DRO if you can.
The problem with DROs is that they are very expensive. It’s not unusual for decent DROs to cost several hundred dollars, and the nice ones are often over $2000. Now, if you’re running a production machine shop, this isn’t a lot more money to add to your capital investments; in fact, your $13000 milling machine probably already has it. But if you’re running machines in your garage as a pass time, it can be tough to justify the extra expense to your wife (unless you commit to an equivalent investment in her pass time, so really the DRO costs double the list price… plus tax).
Enter the Grizzly T23012/T23013 DRO:
I don’t know why it hadn’t occurred to me to look on Grizzly for a cheap DRO; I stumbled across them by accident, browsing the sale items on the Grizzly website.
I had been planning to make my own DRO by modifying a couple cheap digital calipers, but by the time I would have purchased and customize the necessary parts, I would have spent more than the cost of these new.
What’s the catch? These are basically pre-modified cheap digital calipers: they have aluminum slides, plastic housings, and an accuracy certification of +/- .004-inches per 12-inches traveled.
If you can live with this (you can live with this), then these are an amazing deal.
I bought them.
I ordered a 12-inch one for the Y axis and a 24-inch one for the X. This weekend I installed them.
My mill is the G0704, a BF20 type milling machine. I bought it almost exactly 1 year ago, and I love it.
The first thing I did after taking the DRO out of the package was to install the battery and make sure the thing worked. I started removing the screws around the housing and then realized that the battery could be opened by hand.
Right… good start.
I installed the batteries (it takes two, and comes with two spares), and turned it on:
Numbers! okay, on with the rest.
The X axis would be the easier to install, so I started there. I removed the handwheel to get it out of the way for now.
My mill has a dovetail along the length of the front of the table to set stops for left/right cuts.
I’ve never used the stops, so I re-purposed the slot to mount the brackets for the DRO’s rail and used the threaded holes from the stop itself to mount the actual measuring unit.
I had to cut the rails for the DRO to the proper length, but this was easy with a hacksaw.
I had to drill out the rail brackets to fit the screws in the dovetail, but that was also easy enough.
The difficult part here was mounting the measuring unit.
The bracket that came with it was inexplicably designed to hold the unit much further away from the mounting surface than the rail brackets.
In order to use the bracket, I had to flatten it in my vice, and then shorten it to remove the unnecessary bent metal.
As Murphy would have it, I cut the bracket too short, so I had to file a notch in it and clamp it in place using one of the extra stops from the dovetail as a sort of washer.
The washer behind the bracket is my spacer, it keeps the measuring unit perfectly aligned with the rail.
The end result looks cleaner than it is and is actually quite sturdy.
I ran a the table back and forth a few times to verify that the DRO agreed with my handwheel counting and it did.
One down, one to go…