Side to side play in compound rest

[brandon428]

On my 1940's South Bend 9, my compound appears to have side to side play of a few thousandths. If I chuck a tight piece of drill rod, and put a dial indictor on my compound at 90 degrees, I see a back and forth fluctuation of + .003" to - .003 while traversing the compound along the rod. If that isn't clear, I mean I'm seeing 0, .001, .002, .003, .002, .001, 0, -.001, -.002, -.003, -0.002, -.001, 0, etc.

Adjusted my gibs, and even if I tighten them to the point of getting drag, I still get the back and forth play. Problem with the gibs? Wear on the compound dovetail ways?

 

[twhite]

May be stating the obvious but make sure your cross slide gibs are not loose.


Cutting oil is my blood.

 

[francist]

Does it seem to follow in sync with each revolution of the ballcrank? Might be a slightly bent leadscrew kicking it over ever so slightly.

 

[brandon428]

Cross slide gibs are good.

It's definitely in relation to the ball crank. Interesting idea on the leadscrew. I wonder if it could be related to the lead screw nut being slightly offset since it does have a vertical adjustment. I suppose I can check the leadscrew too -- though might be hard to correct if the bend is that minor.

 

[francist]

It's definitely in relation to the ball crank.

Hmm, did you tighten the nut recently in an effort to reduce backlash perhaps? Regardless, sometimes there's a sweet spot where either the nut or a collar likes to be in relation to the crank, especially if there's a bit of wear from age. Might be worth trying a few different levels of snugness to see if it changes. Be aware though, it may be a compromise then of which evil is the lesser -- backlash adjustment or side to side compound wagging?

 

[DavidR8]

"The lesser of two weevils"

 

[silence dogood]

Take apart the compound and check it for bits of foreign material. Clean it, oil it, put it back together, and reset the gibs. Hopefully, that will cure your problem. If not, you may have worn gibs. Had a similar problem, except it was on the x-axis on the mill. It does not take much since it was a little tiny piece of hard goop.

 

[RJSakowski]

Lock the carriage and cross slide and measure again. Play in either of those can cause the symptoms your'e seeing. If one of the those is at play, tightening the compound gibs can actually make things worse as it takes more force to move the compound and you need more cranking force.

 

[brandon428]

I took out the leadscrew when updating to a large dial last year. I didn’t take the nut out, but I did loosen the screw and took the top of the compound off so I could get at everything easier on my bench. I don’t cut tapers with a compound very often, so could easily have missed this.

Is there a method other than trial and error of adjusting the lead screw nut. Now that I think about it, there’s both vertical and potential radial play, and I don’t think there’s a stop, it’s all just adjusted by hand.

I definitely locked the cross slide when I took the measurements.

 

[Jake M]

On my 1940's South Bend 9, my compound appears to have side to side play of a few thousandths. If I chuck a tight piece of drill rod, and put a dial indictor on my compound at 90 degrees, I see a back and forth fluctuation of + .003" to - .003 while traversing the compound along the rod. If that isn't clear, I mean I'm seeing 0, .001, .002, .003, .002, .001, 0, -.001, -.002, -.003, -0.002, -.001, 0, etc.

Adjusted my gibs, and even if I tighten them to the point of getting drag, I still get the back and forth play. Problem with the gibs? Wear on the compound dovetail ways?

I havn't read the whole thing, but craning the compoud, oriented like that, you're pushing and pulling directly in line with the leadscrew and nut for the cross slide, where the's supposed to be some backlash. That's my shot in the dark.

Best is to fix an indicator to the tool post, and check for play against the compound base. As you describe, your measurement makes a complete loop through essentially the whole lathe. Compound to the compound base, the compound base to the cross slide, the cross slide to the carriage, the carriage to the bed ways, the bedways to the headstock, the headstock to the spindle... Most of those are potential wiggly spots. That's too many potential wiggly spots to include in this type of measurement.