[jarekp]

I've had this Grizzly, CNC converted several years back, and no issues up until recently.
It started having a large backlash on Y, but only when the table is offset about 7in to either left, or right side.
It skips about 0.2in on Y, when changing the direction.
Say, I cut a pocket along the X, so it goes along X, then moves only forward on the Y, then back on X.
The problem won't show in such scenario.
But when I do the same pocket with a spiral motion, then it skips about 0.2in on its negative Y motion.
That though, only if I go far enough from zero X, either direction.
If I only go like 4 inches left or right, everything is ok.
I've been analyzing on a pile of two-by-four cut-offs over the weekend, trying to understand what is causing this.
One piece of information that might matter is that I got a nice, good 20lb vise installed on it some time ago.
I wonder if it might be perhaps too much load for the ball nut, when I offset such load way to the side?
Haven't tried without the vise yet, but it's been there for a long time, anyway. And I started noticing the issue
only like a week or two ago.
Checked the coupler, checked the nuts locking the ball screw on the bearing.
I've also added a knob on the back side of the Y stepper last night, so I can try to feel it with my hand, on power off,
and it definitely has that spot with a gap on moving backwards, but it's a floating spot, it's not in a single position of the screw
but it sort of moves along with the nut, but not like with any linear logical connection.
And again, it only does that, when the table is way off the center, about 6-7 inches. within +/- 4inches everything is ok...
I realize something could go wrong with the ball nut, but I'm trying to understand the mechanics of it.
What exactly could have happened in there? How, and why?
That with hope I can perhaps prevent it, or improve that part mechanically. Would double nut help with the load, or it is of no relevance here?

You guys, who know the mechanics of this inside-out, your valuable opinion will be much appreciated.

tia,

jj

[eman5oh]

When was the last time you checked the gibs adjustment? If you have a loose gib you would see a problem like what you describe.

[jarekp]

When was the last time you checked the gibs adjustment? If you have a loose gib you would see a problem like what you describe.

forgot to mention that part.. yes, I did have them inspected. I check and maintain them about regularly..
but since you mentioned, I will run the full adjustment tonight. thanks.

(p.s. I'm not a machinist. other than a weekender/hobby one..)

[KriegKuts]

I would check the balls in the ball screw, maybe you had one shatter or fall out?

[arizonavideo]

Are you sure your not loosing steps?

Set a zero and do the test, then go back and check your zero.

Almost nothing could give you that much lash.