I've got an issue with the Z axis on my mill.
The problem is that when I command the z axis to go up after its been moved down, it will first go down another 5 thousandths or so before it starts going up again. It is a hardware issue and I suspect it is something that is loose. Problem is the way I have the mill setup, it is a pain in the ass to get to the back of the mill and examine the column and ball screw/bearings, etc. If I can make the fix without moving the mill, it will save alot of time and effort.
The mill is a X3 with deluxe fusion kit.
Do you guys have any ideas? Or at least, could narrow it down to a couple possibilities so I know where to start looking?
I've asked about this in the past, and MRM RCModels noted that this happens due to the inertia of the head moving up and creating a bending moment on the column. This is *not* what is happening on my mill. My problem occurs even when jogging by a thousandth at a time.
hmm something similar happens when your steppers are wired incorrectly. can you remove the z-axis stepper and make sure it's wired 100% correctly?
This hasn't been an issue in the past - making me believe the wiring is okay.
The gib definitely sounds like it could be the culprit. As I said, I'm picking this project back up from several months ago (been out of the country over the summer). The gib moves slightly with each change of direction - not a good thing!
I tried adjusting it tighter but didn't have any luck. There is a screw on the top back right side of the head that fits into the notch in the gib. I believe this is to adjust the tightness of the gib? Screwing in is tighter or looser?
Back when I was dealing with this problem for the first time, I think I narrowed it down to the gib, then as well. I even ordered a new gib from grizzly. Unfortunately, the gib they sent out didn't have a notch in it, not sure if it's the wrong gib or what. . .
Appreciate the help guys!
I have an X3 and can agree that it is most certainly the play in the Z axis dovetails. The problem we are up against is that by tightening the gib, it increases friction to the point of binding. There are many posts about providing some means of counteracting the weight of the head to reduce, eliminate this problem. The best approach I ever saw(and the one I will likely someday implement) was a gentleman placed a roller/rollers at the bottom of the head that rode against the center area of the dovetails.
If I can find the link, I will post back.
Yes, that is likely where I saw it originally.
Did you try it with the gib lock loose on it? On mine I notice that when I have the gib loose it reduces the problem tremendously. I found that the gib on these things are slightly mismatched to the dovetail at least thats what i'm thinking. I dropped some braze on the bottom of the backside of the gib to help bring it where it contracts the dovetail more evenly. It reduced the problem .003" - .004". With the gib adjusted too tight with the lock mechanism causes the head to tilt in and out when it first moves.
Have done little reading or research on what others have found with the X3.
My X3 had a gib that was very poorly made (Chinese) 7 thou too thin at one end. Very shoddy.
I made a new gib and it now actually matches the ways.
The roller looks like an interesting solution though I don't feel the need to go to that extreme as of yet.
I've got the gib adjusted to a point. . . when changing direction, the head doesn't move in the wrong direction anymore, but I do have 25 thou backlash in both directions. 25 thou actually sounds fairly reasonable to me seeing as how the Z axis is setup with a belt driving the ball screw (fairly ironic if you ask me). Maybe I should see if I can tighten the belt tension?
And just a thought. . . have people set their Z axis up so that the stepper motor is directly coupled to the ball screw?
Could be some backlash coming from the belt but unless you can see obvious slop then it likely not to be much. 25 thou is a lot.
Look to flex in the cross piece that the ball nut is mounted to. You will be getting some there.
Also make sure there is no backlash in the dual angular contact bearings on the bottom end of the ballscrew.
It is that much. . . 25 thou in both directions, measured with a indicator.
This is at the top inside of the column, where the ball screw mounts?Look to flex in the cross piece that the ball nut is mounted to. You will be getting some there.
And as you said with the dual angular contact bearings, that's at the bottom end of the ball screw? It's been a while since I put this thing together and I'm forgetting what exactly is back there.
Ughhh, I guess it looks like I may be flipping this mill around so I can get to the back of it afterall.