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An Inexpensive DRO for the Mill

Sometimes a thing worth doing is not worth doing well. In this case, I present a very inexpensive no frills DRO for my Industrial Hobbies Mill. Since I intend to convert it to CNC sometime in the next year, it made no sense to purchase an expensive DRO. Yet, it had become clear to me that a DRO would be particularly valuable on a mill, and I do intend to use this mill manually for a while in order to gain maximum familiarity before converting to CNC. After a quick perusal of DRO scales on eBay, it dawned on me just how cheaply this could be done. I rounded up three scales for less than $200 and set to work. I figure when I take the scales off to convert the mill to CNC, I can always put them to use on some other machine. They may even prove useful in calibrating the CNC software initially.

The only thing that gave me the slightest bit of pause on this project was drilling and tapping into the mill castings. Having seen the various detailed photo essays on installing the CNC kit on the Industrial Hobbies web site, I knew it would be straightforward so long as I took it slowly and carefully.

Quill DRO: Z-Axis

The Z-axis seemed the easiest place to start, so I set about making custom bracketry to mount a DRO scale on the Z-axis:

Z-Axis (Quill) DRO

Top Bracket...

Bottom Bracket...

The brackets are all very simple, and made from scraps I had lying around. They're basically aluminum Mic-6 plate cut into appropriate shapes with holes drilled and threaded as needed. I made use of the mounting bracket from the old quill depth gage to mount the lower bracket. The upper bracket attaches to the rear of the scale with 2 screws. A brass rod held in the brackets with set screws ties them together.

The primary challenge on the z-axis is making sure to clear the gear shift levers. In this case, I have a little interference with the Low/High lever at the extreme up level. I sacrificed a little z-travel off the bottom by starting the DRO below the interference. All I need to pick up the lost travel is to replace the socket head set screw with a true headless set screw that sits flush with the bracket. I've never yet fully extended the quill, however, so I probably won't bother. Also note a little bit of scale protruding from the topmost mounting bracket. In fact, I needed a little shorter mounting, so rather than cut down the scale, I just milled the end of the bracket and slid it on through. I have to loosen the bracket to access the socket head cap screw when I remove the scale, but that's no biggie.

The Z-Axis was a piece of cake, X-Axis will be next!

X-Axis DRO

To mount the X-Axis DRO I made use of the travel stop system that already existed on the lathe. This system consists of a center bracket that is fixed to the saddle and does not move when the X-Axis travels as well as two moveable stops affixed to a T-slot in the table's front edge. Step one was to fabricate two mounting brackets to go in the T-Slot. The DRO end brackets would be attached to these two brackets using 10-24 socket head bolts. I just reused to T-Slot Nuts and socket head bolts that were used to mount the original round stops:

DRO mounting bracket in table's edge T-Slot...

I fabricated these two brackets using some 1/2" thick Mic-6 (precision ground surfaces) aluminum plate I had sitting around. Step two is to use the center bracket to attach to the moving DRO head. In reality, we will hold the head stationary on this center bracket while the scale moves under it as the X-Axis moves. The finished head mount looks like this when assembled on the mill:

DRO head attached to the travel stop center bracket...

The primary challenge here is making everything line up without any binding, and doing so in a way that all the fasteners are acceptible. I used the following arrangement to get the job done:

Modified travel stop bracket and the sandwich plate that attaches it to the DRO head...

Making it all work involved countersinking the holes in the sandwich plate (the plate that fits between the DRO head and travel stop bracket), relieving the travel stop bracket to allow access to the 2 DRO mounting screws, milling a groove in the sandwich plate as well as grinding a bit off the socket head to make sure there was no interference with the mill and that the whole works sat in the same plane as the mountings for the ends of the DRO scale. In other words, it took a little bit of fiddling to get right!

DRO Head, Sandwich Plate, and Travel Stop Bracket Assembled...

To make the sandwich plate I started with a piece of squared steel I had laying around from another project. The milling and drilling required were straightforward. I needed to get the countersink depth right on the 2 screws that mount the DRO head to the sandwich plate (you'll notice how small the screws are!), and I found the already completed Z-Axis (Quill) DRO to make that operation a snap.

Here is a view of the completed X-Axis DRO:

X-Axis DRO Complete! I like the way the DRO head is protected under the shelf provided by my Kurt 4" Vise...

One axis left to go...

Y-Axis DRO

The nasty thing about the Y-Axis is that unless something innovative is done about where the scales are mounted, it will be impossible to read without crawling under the table with a flashlight. For this axis I will mount the scale rigidly and move the head, as I have done with the Z-Axis. If you look at the picture immediately above that shows the front of the mill, the idea would be to make a bracket that attaches to the front of the saddle on the left that will grab the DRO head and keep it positioned just in front of the saddle as I traverse the Y-Axis. That should be a pretty convenient spot for it. This may leave the scale protruding slightly beyond the front edge of the mill base if I want to measure full travel, so I need to plan things carefully.

More news when I figure it out...

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