My Boss8 series II has developed Y axis zero problems that started to became detectable
about 3 years ago.

First of all the Y ballscrew was rebuilt about 10 years ago, however usage has been
prototype only, and sometimes isn't used for months. I estimate a max of maybe 3,000 light
duty hrs on the ballscrew. I have checked oiling, and that seems to be okay, at both the ball
nut, and the ways.

It developed into a definite problem about two years ago. After (approx 20 or 30 min)
warm-up, the Y axis would grow approx .0013 in the direction of the column (as if the y
screw was increasing in length from the thrust bearing, as it warmed up) even if the axis
cutting load was virtually zero.

Two months ago I speculated that loosening the y axis gib (I had readjusted it when the ball
screw was rebuilt) 1/8 turn may help (loosen 3/4t then tighten 5/8t) ,,, it did not. In fact, it
made it worse, "the amount of growth doubled!" So now I'm seeing .0025 shift after
warm-up. I instantly moved the gib adjustment to the original position, but this seemed to
changed nothing? I still have about .0025 change in position after warm-up.

And, once things cool down completely, or I restart the machine again at a later date, it
seems to be at the same location it was at the time of the first setup, when the machine was
cold, (not previously running) "y minus .0025" from the warmed up position???

This is a PAIN, and a waste to have to run my machine for 30 to 60 min doing nothing but
cutting air, so the axis is normalized before critical cutting! Then as the machine cools, or
sits, the y axis shrinks, so I have to keep the machine running (and verify y zero) to keep
things accurate!??

Once its warmed up (and I keep it warm) the shift normalizes.


***Any experienced input, or experiences relating to "what could be going on" would be

greatly appreciated***