Cheap DRO! – part 2

Continued from Part 1

With the X-axis DRO installed, I turned my attention to the Y.

The difficulty here was that there weren’t any pre-existing holes or dovetail slots to take advantage of, so it was an entirely custom installation.

The other complication was that the base of the mill flared out to a wider footprint, so the only surface to mount the DRO’s rail on was at an angle relative to the surface on the sliding table itself.

I started by taking off the handwheel on the left side if the table and moving the table all the way to the right to give me working room.
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I then removed the end cap of the table to give just a little more space.
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There was a flat space just under the lead screw that looked like a promising location to mount the measurement unit’s bracket, so I drilled and tapped a 1/4-20 hole in the center of it (approximately).
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Just then my daughter woke up from her nap, so I put things on hold until the next day.

Since I knew I would be modifying brackets, I started working on the rail so that I would have precise references to work from.

After cutting the rail to length,
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I drilled and tapped a hole near the back of the mill first. I placed it so that the mounting bracket would sit just under the line where the base began top taper outwards, this way I could use the same line near the front to visually confirm the straightness of the rail.

In order to avoid obstructing the full range of motion along the Y axis, I had to modify a couple of the mounting brackets and attach them to the front of the mill, instead of the side. The modification was essentially to attach two brackets together (using one of the spare brackets from the X-axis), so that I could reach the front of the base and still keep the rail parallel to the table.

Now that I had the rail mounted, I could get a feel for what sort of bracket I would need to fabricate to hold the measuring unit to the sliding table.

I’ll gloss over the details, since they aren’t particularly useful), but suffice it to say that I used a vice, drill, hammer, and welder to create the necessary Frankenbracket.
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Since this bracket is always hidden under the table, the install looks pretty good.
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The display units conveniently had magnets on the back, so while a long term setup will be a little cleaner, I was able to stick the displays on the head of the mill for immediate use.
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With the installation complete, I turned my attention to re-mounting the vice on my table.
Because of the location of the travel locks and the dovetail slot, The X-axis measuring unit sits about a millimeter above the surface of the table.

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I always keep my milling vice installed on the table, so I needed a way to avoid the top of the measuring unit.

I could shim up my vice, but that would introduce instability and inaccuracy.
So I marked the bottom of the vice where it crossed the edge of the table.
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Then I clamped a large aluminum bar to the table, parallel to the Y-axis (front/back),
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and then clamped this bar in the upside-down vice (I had to space the vice from the bar with a 3-2-1 block to clear the clamping bolts).
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Then I milled out a swath 1.5 millimeters deep and 1.5 inches wide, starting from the mark I made and cutting towards the back of the vice(away from the jaws).
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This was sufficient to clear the measuring unit.
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I re-aligned the vice and now I’m back in business (figuratively.. I don’t actually have a machining business…)
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So there you have it. $60 and 4 hours later, I have DRO on all 3 axis of my milling machine.
I’ll let you know at some later point in time if it lives up to expectations.

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Cheap DRO! – part 1

Cheap DRO!

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:

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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.
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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.
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Right… good start.

I installed the batteries (it takes two, and comes with two spares), and turned it on:
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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.
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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.
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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.
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In order to use the bracket, I had to flatten it in my vice, and then shorten it to remove the unnecessary bent metal.
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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.

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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.

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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…

…and now for something completely different

If you look at my history of posting topics, this one is completely uncharacteristic. However, if you think of my postings as showing off something I did that I’m proud of, this fits right in.

My sister got married last week. I was supposed to give a toast, but her other older brothers and I decided to surprise her (and the groom) with a song instead…