# DRO, another solution



## Rudy (Nov 5, 2017)

I have just finished my DRO mill installation. After searching the wild west web for numerous installations I really didn't find any help for the X axis of the kind I got. I found a solution and thought I would share it with you in case you want something similar on your mill.
I bought a 3-axis unit because I wanted all readings on the same unit. However, the large glass scale proved challenging to install on the Z-axis. The X and Y is straight forward work. The table even had pre drilled holes for the sensor of this kind. I had only X and Y for a while as I where figuring on how to install the Z. Inside of the head was out of the question, not enough room.
It would have been much easier with a smaller caliper type scale, but I had already bought this 3-axis unit. The problem with this type of scales is that the sensor is not supported to the scale. It has to be installed on an object that is tracking the scale, like a mill table. So I had to make a support that slides along the scale with 1mm clearance. I made it with a sliding fit with no noticeable play and no resistance. The next problem is that if you make a rigid bracket between the quill and the sensor, the quill and sensor has to track absolutely exact. Otherwise you will get a bind. A bind would result in a hysteresis in the reading. Making such an accurate bracket was not practical. Something had to be made to allow slight tracking error without affecting the accuracy. If I made one rod on one side of the sensor I also would have a source of inaccuracy since the sensor would possibly bend sideways when changing direction. Again inflicting a hysteresis.
The solution I came up with is a very solid bar out from the quill. This one won't give. Then two steel rods, one on each side of the sensor will allow flex, but not vertically. Any minor play in the quill or sensor slide housing won't be significant to the Z reading.
I tested with a dial indicator on the quill. Coming from above and from below, the DRO and dial indicator are arguing about 0,01mm. Which is the better, I don't know.
BTW. I made a new "grub screw" for the quill. The one preventing the quill from rotating. The original was pretty sloppy and a new one slightly thicker took away all the play.
I love this DRO. I can make things very accurate. Everything bolts together either way when making bolt patterns.


----------



## john_reese (Nov 5, 2017)

Beautifully done.


----------



## MRA (Nov 5, 2017)

This might hijak your thread - in which case, I'm sorry!

But - does anyone know how universal these glass DRO scales are?  I've 'found' an old Heidenhain x-y reader with one scale which works, and one which doesn't.  The real-thing scales are very expensive indeed...


----------



## deeferdog (Nov 5, 2017)

Looks good Rudy. I love reading about machine mods. Cheers, Peter


----------

