X-axis Slop on Lathe

[SteveHGraham]

I feel like I should already know the answer to this, but I am asking anyway.

As everyone knows, lathes have screws to tighten up the cross slide gib. Today I watched a Keith Rucker video, and he took apart an old LeBlond. In addition to the cross slide gib screw, it had an adjustment to keep the carriage from moving in the x direction.

This got my attention, because it seems like my lathe's carriage moves slightly along the x axis when the cutting starts and pressure is applied. It's not a big movement--less than a thousandth, I think--but it's annoying. It shows up on the DRO.

If I poke around under my carriage, will I find something down there I can adjust to keep it from shifting?

[SteveHGraham]

I am wondering if I can adjust this out with the screws and whatever that hold the cross slide nut. I have never touched it, so for all I know it's out of whack.

I found a PM thread on this subject.

http://www.practicalmachinist.com/vb/mo ... sh-172175/

I would refer to my lathe's manual, but it's useless even to Chinese people.

I'm not referring to backlash. I'm talking about a very small movement I get even after taking out backlash.

The lathe is in nearly new condition, so I don't think anything is worn to any significant degree.

[ctwo]

It sounds preposterous, but now I have to go watch Keith's vijeo.

My guess is, why would there be an adjustment if you have V-ways, and what would it bear against, especially if you have V-ways?

I'm also curious how could carriage movement in the X direction show up on a DRO?

[ctwo]

Naturally, I had to start with Part 2 of his series because that looked like where it would be. Not! I think you saw this in Part 1 where Keith explicitly says those ways are unusual, trapezoidal-ways. I probably skimmed over the business where he talks about the adjustment, but I'll guess those are the horizontal screws right at the front the carriage.

I suspect your lathe has V-ways and I suspect the X movement is automatically normalized by virtue of the carriage sitting on a ^ (a Vee, or Wee as Stefan Gotteswinter would say ). You will probably find a gib on the back side that will bear on the underside of your bed-way to prevent the back of the carriage from lifting or cantilevering up under cutting force. That might be loose and worth a look.

[spro]

When "X" means left to right of the carriage, I think it is the "under". The weight of the entire carriage upon the ways is not enough to keep things straight with serious machining. There are gibs of a different way, under the ways to tie it together. They appear to be flat plates but are more than that and I'll tell a few examples.. These wear as do the top ways, not as much but they do. It is an under ledge area and perhaps not finished as well, so those bottom plates/gibs wear. People can take apart and do everything to a lathe and forget these gibs are the ones the saddle doesn't have. The saddle is being squeezed, linearly, between the upper ways and these lower plates/gibs. They are largely unattended, especially the back one. The plate can be removed and ground/filed Flat. The shims adjusted so when bolts tightened, slight drag.

[spro]

And keep those ledges clean and lubed!!! ( Nurse Ratchet and perhaps another).

[GlennW]

The question would be which axis you are calling "X".

"X" should be the cross slide. So the "X" axis scale should be attached to the carriage, so movement of the carriage should not affect the "X" axis reading as the scale shouldn't see it.

[spro]

It confused me too. I went with what I thought was happening by the description. I defer to best interpretation.

[ctwo]

Now I'm confused too. I'm wondering if the movement is still in the cross slide? Might be thrust washers on the screw? But you've taken up the slack, so it can't move!?!

[spro]

O.P.'s third sentence. I think he's describing the "carriage lock" which drove me to thinking about the underside jibs. Almost every lathe I use has larger nut and/or special box end wrench to tighten that. It isn't the same but for similar purpose.

[Magicniner]

In addition to the cross slide gib screw, it had an adjustment to keep the carriage from moving in the x direction.

X-Axis slop on a lathe combines the backlash in the cross slide and any front-to-back movement of the carriage at right angles to the bed, the design movement of the carriage is in "Z".

On most machines with a spindle "Z" is the axis which moves parallel to the centre line of the spindle, this is the case on a conventional lathe where the cross slide moves in "X" and the carriage moves along the length of the bed in "Z", if you have a vertical milling slide on your cross slide you have something that moves in "Y"

- Nick

[spro]

Well then I must make amends somehow for perpetuating an archaic way of describing the travel. I was ..likening it to a vertical mill where X was perpendicular to Z and Y wasn't a problem except U meaning underneath. I will stifle and learn.
Edit to say.. I think we are talking about the same thing.