Cross slide handle misbehavior

[AllenV]

I am seeking advice on a long-standing issue with my lathe. What I have is an Enco 13x40 built in 2006. I bought it new.

Since new it has had an annoying habit of letting the cross slide feed handle back off counter clockwise when the “stick” on the handle is oriented such that gravity pulls it down. It will “fall” until the backlash on the screw is taken up. The problem matters while doing a turning operation. If I set the cross slide for a fresh cut and that happens to be where the “stick” handle is on the left side, then if I let go of the cross slide feed handle the handle will rotate CCW by gravity. This CCW rotation removes the screw pressure holding tool pressure on the cross slide. Then the cross slide moves away from the workpiece until the screw is engaged again. If I HOLD the handle, all is fine.

Note that I am not describing a backlash issue. The backlash is set by a split nut with wedge to 0.009” at the moment. The root issue is the handle and screw rotating CCW when the “stick” is on the left side and can thus move down by gravity.

I can see two paths forward:

1) Balance the wheel. Attach weight to the non-handle side.
I see that fancier lathes have balanced wheels. But some really nice machines don’t.

2) Try to increase the friction of the screw rotation.
The parts diagram (below) shows the screw is supported by a pair of opposed thrust bearings. I suppose I could tighten the nut and hope for more friction. It could be that all I get is over tight bearings with lumpy rotation.

Any suggestions or advice? Have any of you fixed this problem or your machine?

 

[Jim F]

Snug up the gibs ?

 

[AllenV]

Snug up the gibs ?

I'll readily admit that I have not measured the play in the cross slide and the gibs are where the factory put them. But, I don't see that the gibs are a potential root cause. Tighter gibs would just slow down the movement of the cross slide after the handle/screw rotate away.

As it is I don't get chatter or poor finishes unless I screw up.

 

[Jimsehr]

I think if the gibs don’t hold the handle in place they are not adjusted enough.
in 70 years of machining I have never seen this problem.
tighten the gibs.

 

[ChazzC]

I think if the gibs don’t hold the handle in place they are not adjusted enough.
in 70 years of machining I have never seen this problem.
tighten the gibs.

I agree: I have tried several unbalanced hand wheels on my 7x16 and never experienced unintended rotation, and mini-lathes are notoriously non-rigid. I would expect that a 10x40 lathe of any pedigree would perform magnitudes better.

 

[Jake M]

I am seeking advice on a long-standing issue with my lathe. What I have is an Enco 13x40 built in 2006. I bought it new.

Since new it has had an annoying habit of letting the cross slide feed handle back off counter clockwise when the “stick” on the handle is oriented such that gravity pulls it down. It will “fall” until the backlash on the screw is taken up. The problem matters while doing a turning operation. If I set the cross slide for a fresh cut and that happens to be where the “stick” handle is on the left side, then if I let go of the cross slide feed handle the handle will rotate CCW by gravity. This CCW rotation removes the screw pressure holding tool pressure on the cross slide. Then the cross slide moves away from the workpiece until the screw is engaged again. If I HOLD the handle, all is fine.

Note that I am not describing a backlash issue. The backlash is set by a split nut with wedge to 0.009” at the moment. The root issue is the handle and screw rotating CCW when the “stick” is on the left side and can thus move down by gravity.

I can see two paths forward:

1) Balance the wheel. Attach weight to the non-handle side.
I see that fancier lathes have balanced wheels. But some really nice machines don’t.

2) Try to increase the friction of the screw rotation.
The parts diagram (below) shows the screw is supported by a pair of opposed thrust bearings. I suppose I could tighten the nut and hope for more friction. It could be that all I get is over tight bearings with lumpy rotation.

Any suggestions or advice? Have any of you fixed this problem or your machine?

I think I understand what you're saying, and I agree with you, I don't think it's the gibs. The gibs could be all loose and falling out for all I know, but the problem you describe, I have with my compound rest. Gravity exceeds the friction of the screw, so the weight of the handle moves the screw to the opposite side of the backlash, right? Then the work/tool pressure moves your cross slide? BECAUSE the screw was not in position?

My cross slide does not use bearings, just shims. I havn't tried to make or find shims that could balance friction that well..... If mine had bearings, I'd have already tried to preload those. The preload to "just barely snug up" the screw rotation is (depending on the bearing design) going to be too tight, but not enough to bother. This is low speed stuff. That would be my first go at it. Crunchy bearings don't happen at a little too tight, they happen at a way too tight.

Balancing the handle might well solve the problem, but it's still gonna need to be watched, as there's lots of reasons that screw might still want to do something besides just sit there. I think that a -light- friction in the screw, by one means or another, would probably be your best bet.

I'm still working out what to do about mine, as mine is an old, all original machine that I don't want to cut up. I'll come up with something one day, but whatever it is, it will be something to deliver a good, smooth, non-wearing friction.

 

[jwmay]

I think you ought to try to balance the handwheel, and use the wedge adjuster for greater friction between screw and nut. Or just use the wedge adjuster, and don’t bother with the handwheel. I’m pretty sure that’s the purpose of the wedge adjuster.

I don’t see any way in my imagination that the tightness of the gibs can be blamed for a loose leadscrew/nut interface.

 

[ChazzC]

Lock the cross-slide when making longitudinal cuts?

 

[OTmachine]

Maybe something like this?

 

[jwmay]

More like these, but not exactly.