Three Axis
Generic Digital Read Out
On A
Generic Vertical Mill
29 May 2015:
I've finally decided to go ahead and pull the trigger on a digital read out for the mill.  With it, I will be able to make mistakes with much greater accuracy.

My mill is a Grizzly G 3102.  The DRO kit I decided on is a DRO Pros Model 3M (DROPROS.COM).  The kit arrived well packed and in good condition.
All the smaller boxes were packed inside a larger box with styrofoam peanuts.                         Here are all the pieces.                                     
After unpacking everything and sorting out the parts, I decided to do something novel and read the instructions.  It's good that I did because there are some fiddly bits to the alignment.  If alignment is not correct, the linear scales will be damaged.

Of course, the instructions showed installation on a different type of mill so I had to do some head scratching.  The first vector I decided to install was the "X" vector (left-right).  There came the first surprise.

I guess it figures that it's only been about a month since I completely disassembled the X-Y table for cleaning and tramming. I had to disassemble it yet again to put on the X vector scale and reader.  At least, it was clean (mostly) this time.
Mill disassembled for installastion of X readeout.
The location of the scale and reader is at the rear of the table and there isn't enough room to get a drill for the mounting holes.  In addition, that's a really crummy way to drill the holes because a hand drill has to be used.  Did I mention that those parts are HEAVY?
X axis centered on Y axis table.                                                                                  Inserting gib.          
Before disassembly, the table was moved to each end of it's travel and marked then the center was determined.  To keep it in place on the carriage, the gib was put in place and tightened to lock the table to the carriage.

Tightening gib to lock table in position.
                            Initial test layout.                                                            Marking knee shield mounting plate for sensor clearance.
After having figured out just how to mount the parts, I had to modify the clamping plate that holds the sheet rubber knee way shield in place.  This consisted of filing a notch in the plate.

Using a "Swedish mill" to modify shield clamping plate.
Ideally, making the clearance notch in the clamping plate would be a piece of cake using the mill.  Unfortunately, mill was unavailable for the job so I had to resort to my "Swedish mill".  A few drops of sweat later, the chore was done.

The notched plate.
Next, a piece of lightweight angle was modified to be used as a mounting plate for a shield for the scale and reader.  They really don't like to be filled with chips.
Parts positioned for mounting hole layout.                                                         Test fit after drilling and tapping.    
The X vector parts are now ready to go.  They'll have to be removed before the mill can be reassembled, then re-installed and aligned.  I'm going to work on the location  of the Y vector encoder and sensor before putting the mill back together.  It may be that I have to do some work with it apart.

The Z vector should be the easiest to do.
30 May 2015:
After some study, I decided I could put the Y axis back on the mill.

Now for the Y axis scale and reader.  Using an existing hole on the Y axis table, I temporarily mounted the Y scale mounting bar.  After temporarily laying the X axis table on, I found that the first option wouldn't work.
Finding the centrer of movement of the Y axis.                                             Test fit of mounting rail showing interference.
As you can see in the above right photo, the X table interferes with the sensor bar by about 0.5".  The solution was to make a couple of plates to lower the bar by
 0.625" so the X axis has full travel.
Lowering plates in place.                                                                                   Checking alignment of bar.
With the scale bar mounted, it was checked for horizontal alignment and adjusted until it was within 0.001" throughout the Y axis travel.  After the reader mounting is completed, vertical alignment of the scale will be done.
In spite of the photo, the scale bar now clears.                                               Here it is with the scale temporarily mounted.  
I'm not too pleased with having to cantilever the scale but there's no better way to do it.  Since, when the scale is bolted to the bar, it's a pretty rigid assembly, I don't anticipate trouble.  Another thing in it's favor is that it is more or less out of the way so it has little chance of getting bumped.

As you can see, the scale obscures the hard stops for the Y axis.  This is not really important, as the stops can still be adjusted if it becomes necessary.  You will also notice that I've un-mounted the control box.  The scale bangs into it when the Y axis is moved toward the operator.  Once I've got the rest of the Y axis done, I'll re-mount the box about an inch lower so the scale clears.

More thinking will be required for the reader mount.  It's going to be a couple of inches to the side of the knee so the mounting needs to be very rigid so the alignment doesn't suffer.  With the way the scale is mounted, there's no room for flex in the reader mount.

31 May 2015:
I spent about a half day on the project today.  I now have the Y axis installed and the mill is going back together.

Y axis sensor mounting bracket.
It took longer than anticipated to mount the sensor because I had to make some posts to hold it securely.  Getting the scale adjusted so it was tilted so as to be parallel with the Y table was a pain.  The mounting screws for the scale are slotted and it is difficult to get it to indicate less than 0.005" from end to end of travel.
      Y vector scale and sensor in place.                                                    Z scale and sensor laid where I think they should go.
I used the chip shield that was supplied but added a "skirt" to help keep crud out of the scale.

Before replacing the X table, I laid the Z vector scale and sensor where I think they should be  I'm not happy with having to locate it where it is because it's going to be hard to adequately shield it from chips and crud.  You will ask why I didn't get a smaller scale and sensor and put them on the quill.  The reason is that the quil is a little on the sloppy side and I prefer to lock it in position and use the knee for the Z movement.

Tomorow, I will finish putting the mill back together and mount the X axis scale and sensor.  Then, I'll mount the control/readout and test the X and Y vectors.  Afterward, I may have thought of a better way to do the knee sensor.
1 June 2015:
The X and Y axes are done and tested.  
X and Y finished and working.
The wiring is semi neatened but that little chore has to be finished when I get the Z axis done.  I'm still thinking about how to get the Z axis installed in such a way it doesn't fill up with chips.

A thought on buying a mill with no bells and whistles and having to purchase them later and install them.  In a word, DON'T DO IT!  Go ahead and knock yourself out with a machine that has all the options you think you'll need.  You don't save any money buying a stripped machine and then have to do all the work.  After all that, there's no warranty on the installation.  Sometimes, being a skinflint will jump up and bite you.

After having gone through the process, I think I'll be very happy with my "custom" mill.
3 June 2015:
Today, I went ahead and mounted the Z axis scale and sensor and got it working.  I still haven't figured out just how to go about shielding the scale and sensor from chips and oil but it will come to me.
Cutting the end off of the supplied mounting bar.                             Mounting bar stub in place atop scale.      
Since the mill frame is tapered, in order to get the scale truly perpendicular to the knee, I had to resort to some creative hacksawing*.  The scales each came with a mounting bar that allowed the scales to be adjusted but, since the taper of the mill frame was too much for the stock bar and there being a lack of clearance when the bar was used, I simply cut one end off of the bar.  It was bolted to the top of the scale and, using a spacer and some longer bolts, allowed for the scale to be offset enough to get the scale to within 0.005" of true throughout the full range of Z motion.

*: I would have used my bandsaw but, yesterday the gearbox finally gave-up the ghost.  I think the worm gear has worn out but I won't know until I get it apart.  If the gear's shot, I'll have to get a new bandsaw.  That one was given to me a few years ago because the owner couldn't get it to cut straight.  Some creative filing, hammering and cursing got it to cut reasonably well but it was semi-junk then and is total junk now (if the gear's worn out).  For what it cost me, it's given very good service.
                             Cutting unwanted part off of supplied bracket.                                  Bracket in place at lower end of scale.                        
The bottom mounting of the scale consisted of simply bolting it to the mill frame and shimming it to be parallel to the plane of the knee.

The sensor was mounted using one of the supplied brackets, modified to fit.  It was cut as shown and two oversize mounting holes were drilled (arrows) to accomodate final adjustment.  The sensor also had to be shimmed to run true along the length of the scale.

Z scale and sensor in place.
As you can see, the scale is right in the path of chips and crud, so it's going to be necessary to work out some kind of shielding for it.

All three axes working!

After getting the axes to read in the correct direction, I now have a mill with a power X feed and digital readouts.  All I gotta do now is learn to use all of the el-neato functions of it.  Am I up to date or what?

I still have to do the shield and neaten-up the cabling so this isn't the end of the saga.
5 June 2015:
I wasted a good part of the day attempting to figure out a way to make chip shields and ended-up simply enlarging the knee chip shield so it covered the Z scale.

Z axis chip shield in place.
I'm still not sure this is the best way to do the deed but the scale and sensor are protected from direct hits from chips.  The gray material I'm using for the chip shields (except for the black rubber shield directly adjacent the spindle) is some trimmings from a shower pan sealing job.  I think it will work all right because I soaked a piece of it in paint thinner for a week and it wasn't softened at all.  The black rubber will resist hot chips better than I think the gray stuff will.

Now, I'm ready to have fun. 
Still having fun!
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