[cds333]

I did not notice this before now, due to the fact that this only happens at a range that is pretty low on the Z axis- usually with larger endmills I never go this low on the Z, but when I installed an 1/8" endmill the other day I noticed the problem.

As you can see, reversing the direction of the Z axis causes the entire head and spindle to shift laterally a significant amount. You don't even need the indicator as this motion is visible to the eye by simply watching the machine. However doing so at other places along the Z axis do not cause this problem.

The large dial indicator is for the X movement, the small indicator is for the Y, although there is no significant Y movement.

So what is causing this? And why is it only happening at a specific point, but not above or below that point?

And how would I fix it?

Thanks very much!

[cncuser1]

If this only happens on a certain portion of the travel then it is probably the ways on the column.

First off make sure the gib is properly adjusted, that it is only rubbing on the face opposite where the screws push against it. Then make sure the actual screws are properly tensioned. If that doesn't help then lookup how to accurately measure the width of ways of the column with dowel pins and a good caliper or micrometer. If the ways are not consistent along their entire length you might have some way scraping in your future if you want to eliminate this.