Millrite DRO

[lazlo]

Last Summer, I posted a DRO bracket I made to mount a glass scale on the Burke Millrite knee:

http://bbs.homeshopmachinist.net/showthread.php?t=29714

I just sold the Millrite to a friend in the Austin Metalworking club, so I figure I might as well show the rest of the DRO install

The Burke was designed in the era before DRO's -- there's virtually no flat spots on the entire casting except for the front of the table, so I had to make custom compound angle spacers for the Y- and Z-axis.

This is (was) my Millrite. What's hard to tell from the angle of that picture is that the knee has ~ a 2° downward draft, and a 1 1/2° backward draft. To complicate matters, the turret base is a squared-off conical section, so the area next to the Z-ways is curved, and sloped backward up to to turret by about 3°:



The easiest part of the install was the X-axis scale. The Millrite table closes all the against the Z-ways, so you can't install on the back side of the table like you'd normally do on most Bridgeport clones. The complication here is that the factory-installed Servo power feed needs the feed stops on the front of the table. The reader head for the glass scale needs to go there, but a feed stop hitting the reader head will destroy the scale. So I made a bracket that completely encases the scale reader head, with a hollow track to bring out the armored reader head cable behind the bracket. This allowed the Servo feed to be mounted on the reader head bracket.

You have to make sure to maintain the correct gap between the glass scale and the reader head (1 mm), so I mocked it up after I marked it out, to insure that the mounting holes for the glass scale, the reader head (which is fixed to this bracket) and the Servo feed stops all fit together:



Here I'm milling-out the pocket for the reader head:

[lazlo]

Another complication of this install was that the previous owner (a lurking member here), had apparently installed a DRO on the machine before me. He had drilled and tapped 3/8" holes in the front of the table and on the side of the knee, and I wanted to minimize the number of holes I drilled in the machine.

Unfortunately, the Jenix DRO system I was installing had all Metric hardware...

So I made these ugly 3/8" -> 8mm thread adapters, so I could install the Jenix scales into the 3/8" holes:
A piece of 3/8" All Thread with a spacer and a jam nut. Bored and tapped the center for 8mm:



Then cut off the length to the depth of the hole, and cut a screw slot with a slitting saw. I used these adapters on the X- and Y-axis:



But not all the previous holes were in the right places for the Jenix scales, so I used a magnetic drill press to drill the holes perpendicular. This is a Jancy Holemaker -- 30 lbs, with a coolant system, very nice unit:



This was the first time I'd used a magnetic drill press. It's a little tricky to get the 30lbs slung into an awkward position before you trigger the electromagnet. But like the electromagnet on a surface grinder, it takes a couple of second to de-energize, so what I found that works is sticking it in the general vicinity of where you want to drill, then turn off the electromagnet, nudge it closer to where you need it before it falls off, and quickly turn the electromagnet back on.

Of course, that magnetizes any metal objects within 4" or so of the electromagnet, including the cast iron dust from the hole you're drilling:

[lazlo]

Mounting the reader head bracket on the Y-axis was even more fun...

On a Bridgeport, you normally mount the Y-axis reader head bracket on the saddle. But on the Mllrite, the saddle has a cut-out where the Y axis leadscrew and nut carrier run on the side. So mounting the reader head like a Bridgeport would have required a plate to go lengthwise, then down, and then an angle piece back in to the plane of the scale/reader head.

Mounting the reader head bracket on the nut carrier bar itself would be a lot cleaner, but it's roughly cast iron. Drilling it for the mounting holes was miserable, so I knew that milling the end flat (so the reader head would sit flat), was going to be a problem:



I pulled out a hand scraper, and even with a freshly sharpened carbide blade, it just skipped off the hard casting skin. Even my Biax (power scraper) just ricocheted off it. I thought about using an angle grinder to take off the skin (I know, I know...), and then decided to try something dangerous and stupid: I mounted a 3/8" carbide endmill in the magnetic drill press, mounted the drill press sideways on the knee, and gently skimmed off a couple of tenths at a time by feeding the table in:



After a bunch of passes, I had the nut carrier block cleaned up very nicely:



Which made installing the reader header bracket a breeze:

[lazlo]

The Y-axis spacer for the scale mounting beam was a lot of work. This is where the knee castinghas ~ a 2° downward draft, and a 1 1/2° backward draft. From what I've seen on other DRO installs, you can either make stacks and stacks of shims, and hope everything stays tight, or you make a custom spacer on one end to use the other end of the bare casting as a reference point. I chose the latter route.

You can see where I tried to blue it, but you really can't get any kind of a decent transfer on a painted surface. I tried measuring the inward, and downward slopes, but that was hopeless. The scale and the reader head have to be flat and parallel to within .1 mm (4 thou) across the entire length of the scale. Between the irregularities in casting, and the paint, I couldn't get a clean enough measurement. I ended up installing one end of the scale mounting beam and measuring the offset in both dimensions with a DTI:



Then I made a round spacer with the correct angles:



This is the final spacer:



I installed it by marking the high spot on the spacer, installing the spacer, placing a DTI on the scale mounting beam, and then rotating the spacer until I minimized the "runout" of the beam:

[HSS]

Lazlo, I am impressed. Excellent post and pics. Not bad at all......... for a Texan.

Patrick

[JCHannum]

Good post Robert. That is a nice professional looking job.

I particularly like the magnetic milling machine.

[lazlo]

Thanks guys

I'm going to post one final piece about the Y-axis, and then create a separate thread for the Z-axis, which was a odyssey into itself. Not to drag it out for another thread, but I don't want to slog anyone's 'Net connection with 30 pictures on a single thread...

The final part of the Y-axis install was to recess the mounting screws on the aluminum bar so that glass scale would sit flat. I used this bar because it came with the Jenix mounting supplies, but it might as well have been a blank bar, since none of the holes were going to match the mixture of Imperial holes in the Millrite with the Metric 8 mm and 6 mm mounting screws on the Jenix scales. The lower left hole on the bar in the picture is an 8 mm through-hole, and here I'm drilling the counterbore for the 3/8" cap screw. The hole location was tricky -- you can see that I barely have enough room for a 3/8" counterbore.

Also, the Jenix mounting bar wasn't thick enough for the counterbore, so I had to grind down the cap screws for a Poor Man's low-profile socket screw. This is one of those times I wish I wasn't using Unbrako screws



And finally, here's the Y-axis completely installed:

[Peter Neill]

I missed this earlier on, so I'm glad I've seen it & it's companion post now as it's all rather good.
Nice work all round.

Peter

[Tim The Grim]

Lazlo,

I'm really glad to see you are doing such great things with my previous mill. Here I am looking at the 1st photo saying to myself, " WOW ! He even has the same old mill drill as me". Then I realized that was my old garage and I had taken the picture. Anyway...Beautiful job on the DRO and this thread. I wish you much success.

Tim

[lazlo]

Hey Tim -- great to hear from you! Tim sold me the Millrite a couple of years ago

One last picture that I had to get from the new owner: I forgot to take a picture of the enclosed reader-head bracket with the internal cable guide described in the first couple of posts. This bracket holds the reader head, and also protects it from crashes from he Servo feed stops: