X-Axis slop ... need advice

[Jay C]

Wasn't sure to use this forum or the benchtop forum, but either way I have an issue with table slop on my X2 Mini mill in the X-axis.

I don't think it's backlash. I say this because I can move the table 5thousands of an inch despite the stepper being locked.

What I've done thus far:

• I tore the X axis apart last week, reballed the Nook nut (CNCFusion kit BTW) with 1.259" balls
• I can tighten the gib to the point of locking the table, then back off slightly and the problem is still there (stick slip).

Have a look at this short video and let me know what I should do next please.
"http://www.youtube.com/watch?v=E5z-vKtxVP4"]YouTube - X2-table slop

[Jay C]

Well shoot, I did a search for slop and found this:

X2 CNC Fusion - Replace Lovejoy Connectors?

So it looks like the spider coupler is the culprit ... doh!

You guys agree?

Jay

[Jay C]

I've looked at the helical, oldham, slit disc, and uniflex. here

• I actually have a small helical (came with some encoders I bought) ... but it has a lot of axial play.
• The oldham might work ... what say you
• Slit type ... look like helicals to me
• Uniflex (OMFG these things are pricey)

CNCFusion sells a Helical coupler for 0-backlash, but from what I've read there is axial play which is what I think I'm battling.

Jay

[MrWild]

The slop talked about isn't the slop you have. Ifyou redid the ball nut, the problem could be in your thrust bearings.

[Jay C]

The slop talked about isn't the slop you have. Ifyou redid the ball nut, the problem could be in your thrust bearings.

I suppose, but why do you say it's there an not in the coupling?

Also, the thrust bearings I'm using are the ones that come on the X2 originally ... they are being reused. Just simple ball cage sandwiched between two steel races seen here. There are two bearing actually. one on the inside, one on the outside. The outside one is held in place with a clamp collar.

Jay

[kawazuki]

Easiest way to elliminate the coupling is undo one of the grub screws and put some squeeze pressure on and re-tighten. Or take apart and ooze some silicone mastic on all the faces, re-assemble, leave to go off and you should have a flex joint without slop?
Thrust bearings does sound a good culprit though!

[philbur]

It cannot be the coupling as you have axial play. If you totally removed the coupling the axial play will be the same. Think about it, the thrust bearing connects the ballscrew to the table, not the coupling.

X-axis axial movement (relative to the base) is controlled by the ballnut, the thrust bearing and the Y-axis gib. One of then is not adjusted correctly. Use your DTI with a bit of thought to find out which.

Phil

PS: the slack looks bad enough you should be able to see where it is without the DTI.

I suppose, but why do you say it's there an not in the coupling?

Also, the thrust bearings I'm using are the ones that come on the X2 originally ... they are being reused. Just simple ball cage sandwiched between two steel races seen here. There are two bearing actually. one on the inside, one on the outside. The outside one is held in place with a clamp collar.

Jay

[Jay C]

It cannot be the coupling as you have axial play. If you totally removed the coupling the axial play will be the same. Think about it, the thrust bearing connects the ballscrew to the table, not the coupling.

Yes and no. The ballscrew attaches to the spider coupling which attaches to the x-axis stepper, which is attached to the table.
"http://www.youtube.com/watch?v=q741HJJEYeg&NR=1"]YouTube - 33: Sieg X2 Mini Mill cnc x,y Axis Convertion part4 (skip to the 8-minute mark)

X-axis axial movement (relative to the base) is controlled by the ballnut, the thrust bearing and the Y-axis gib. One of then is not adjusted correctly. Use your DTI with a bit of thought to find out which.

Phil

PS: the slack looks bad enough you should be able to see where it is without the DTI.

Well no I can't see where it is. The only thing I hadn't adjusted was the Y-axis gibb. I locked it down tight but the same slop is there. Yes I can see the slop (I can see the table move) but the fixed end does not. I can hear the movement, but I can't see where it is. I can use bigger balls, but to be honest, I saw no change in the slop with the new balls.

What now? The DTI tells me there is slop, I can see the slop. I think it's in the spider coupler, some think it's the thrust bearings. Help I can't see the forest for the trees.

Jay

[Jay C]

Update: I watched the videos done by Quadrant2005 again. He suggested moving the X-axis to the far left so that the left hand side was pushed up against the table. I did this, then use a bar clamp to put a lot of pressure on the shaft clamp as I tightened it. End result 0.0005" backlash. So it was the thrust bearings. Now I'm off to do the same to the Y.

Thanks to those of you that replied, I heard you, but I wasn't getting it.

Jay

[LUCKY13]

OK , it sounds to me like you have forced the slack out and clamped the lovejoy down to hold the slack out. THis is probably not a good way to do this. If I understand what I was looking at in the video there is no thrust bearing on the motor side, it is on the oppisite side where the hand crank is. What you have done will take the slop out, but now you have pressure on your motor shaft and this will cause wear/problems latter on.



I think what I would do is go to the side that has the thrust bearing and look at its design. There needs to be away to shim it so that it holds the screw from moving in those directions. Its seems to me that there would need to be some kinda locking nut on the thrust bearing side so you could shim this bearing to take the slop out and not need to reley on pressing the screw in one direction and locking the motor and lovejoy down to hold it. This will wear your motor and lovejoy.

You should be able to take the motor and the lovejoy totally off and there be no slack in the table/screw set. This is how it needs to be done. What ever it takes to make it that way is what you need to do. And it will be with the thrust bearing setup that you will be able to achive this.


Jess

[philbur]

You should preload the thrust bearing in order to remove slack. Not preload the coupling to remove slack in thrust bearing. Your motor bearings are probably currently taking the load, which is not good.

The thrust bearing is there to transfer load from the screw to the table without any axial slack. As I said previously the coupling should take no part in this. If you are using or "adjusting" the coupling to remove axial slack you are doing something wrong, period.

You need to workout how to preload the thrust bearing correctly.

Phil

Update: I watched the videos done by Quadrant2005 again. He suggested moving the X-axis to the far left so that the left hand side was pushed up against the table. I did this, then use a bar clamp to put a lot of pressure on the shaft clamp as I tightened it. End result 0.0005" backlash. So it was the thrust bearings. Now I'm off to do the same to the Y.

Thanks to those of you that replied, I heard you, but I wasn't getting it.

Jay

[philbur]

A final thought. If you can influence the axial slack by fiddling with the coupling it means your thrust bearing MUST be slack and needs adjusting (preloading) correctly.

Phil

You should preload the thrust bearing in order to remove slack. Not preload the coupling to remove slack in thrust bearing. Your motor bearings are probably currently taking the load, which is not good.

The thrust bearing is there to transfer load from the screw to the table without any axial slack. As I said previously the coupling should take no part in this. If you are using or "adjusting" the coupling to remove axial slack you are doing something wrong, period.

You need to workout how to preload the thrust bearing correctly.

Phil