Lathe - Barber Shop Pole Pattern, Loose Carraige?

I would have to say your problem lies in the spindle bearings. Whether or not it can be fixed by adjustment remains to be seen. I had a very similar problem on my Enco 9x12. In my case the problem was present as soon as I bought it.
I suggest you try this. Put a pice of drill rod or similar in a colett or 4-jaw chuck and then see how closely an indicator reads when rotating the spindle. In my case it was impossible to get it dead nuts because a high reading showed up on every second revolution no matter what I did. A sure sign of a bad bearing. Adjustment did nothing. I replaced the bearings and the problem disappeared . I don't know exactly what the problem was with a bearing but the rotation of a bearing will bring any given ball or roller around to the same spot on 2 revolutions.


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what tooling are you using? I have seen that with a tool with to much radius. And also with a dull tool. Does the part get hot when you are turning it?
 
I have seen similar patterns in turning and facing. I attributed them to high frequency chatter at the time. My thought was the effect similar to the washboard effect on a gravel road. The first hole creates an oscillation in the vehicle which in turn starts the next rut and so on. As to what is allowing the chatter, something loose; spindle, gibs, etc. If you are using power feed for facing, possibly an irregularity in one of the gears?

Considering your first attempt at facing did not have this problem, my inclination is to agree with Jim and Ronzo about a loose spindle. It looks like the oscillation frequency is 27 times your rotational speed ( I count 27 spirals). What would the pattern look like if you were to use a center in the tailstock? Does it go away or change appearance? The tailstock center should change the restorative force and change the frequency. What does the pattern look like if you change feeds and speeds?

Good luck with sorting this out and please update us on your findings.

Bob
 
Update: I measured about .001 movement in the spindle end play so I tightened the spindle real quick about that just for a quick test. The spindle still spins fairly freely but I can detect some sticktion at the start of rotation. This did not eliminate the spiral pattern but did change it, roughly doubled the number of spiral lines on the OD, if these were rings on a tree the spiral pattern now has double the number of rings.

I also took a face cut with the carriage locked, no difference eliminating the loose carriage theory.

I guess I'm going to follow the Grizzly procedure now, remove the chuck, loosen the spindle .100 per the manual and re-adjust to spec. I may re-install the factory 3 jaw to eliminate the 40lb PBA as the possible issue though I seem to recall this issue prior to installing that chuck.
 
what tooling are you using? I have seen that with a tool with to much radius. And also with a dull tool. Does the part get hot when you are turning it?

I'm using indexable carbide tooling, the radius is quit small maybe 1/32 and the inserts are razor sharp. That said when I turned a steel shaft last week using a different insert for steel that's not sharp at all and I got the same spiral pattern. So different materials, different diameters, speeds, and feeds. The brass is turning nicely except for the weird spiral pattern.
 
Well, you could always sell that disk to a hypnotist. (You are getting sleepy, sleepy........)
 
I read all the suggestions and a lot of good advice. Since the pattern is there both turning and facing its most likely in the headstock. Spindle bearings first, then motor bearings and belt. I think it'll a bad ball somewhere. They won't check as being loose but will set up a pattern.
A .0001 indicator set on the spindle nose will sometime show a bad bearing ball. You have a nice machine, I hope you find the problem.


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Hmmm, let me check the crystal ball. Yes, I see a new 16x40 in your future :grin:
 
Jim you are an instigator!! My money is on belts at the moment, I'm going to tighten them, they are loose, link belts by the way.
 
Spindle bearings have been mentioned several times. But,also check that the lead screw isn't a little bent. It can also cause finish problems by making the carriage ride a little bit up and down as it turns.
 
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