Poor Finish and Strange Helical Patterns

J

Jecheon

Registered
Registered
Hello,

When using my Regal 10" lately I'm getting a very poor surface finish. The work is aluminum, I'm using sharp HSS tools, the diameter of the work is about an inch, and the speed is set to 350rpm. I'm taking a light cut and using the slowest feed I can (224 turns per inch). Unfortunately, I keep producing an unusual helical pattern on the surface of the work; you can actually feel the gentle peaks and troughs of the helix with your finger.
I'm fearful that this may be the result of worn spindle bearings, although I can detect no movement in them, even if I use a 4/5ft wooden leave under the chuck. Despite being old (1940ish), everything seems solid to me and I can't feel or see any untoward movement during operation. Nor does it seem particularly noise to me in use; the bearing seem quite (although the front set do drink a bit of oil), and there isn't much noise from the gear box. The motor does hum a bit and produces a little vibration, but I don't see how this can translate to an undulating finish unless there is excessive play elsewhere. Does anyone have any ideas to what the problem is likely to be, or how to investigate the cause?

You can see the pattern in the photo attached (I've altered the contrast a bit to make it more visible).

Pete

Picture 001a.jpg
 
That pattern is chatter. Before you break it down check that everything on the slides ans apron are tight, Gibs on both slides could be the culprit. Make sure the tool height is correct. From then on you are probably correct. It is the spindle bearings themselves.


"Billy G"
 
Pete,

That doesn't look like chatter that would result from a less than rigid set-up, although I assume you have minimal tool and part overhang. Have you checked the spindle for end play?

BTW, a 1" aluminum part should be turning at 1000 rpm or more, although that isn't what's causing your problem.

Tom
 
I gotta say that looks very much like how my steel pieces were turning out just before I replaced my spindle bearings, although aluminum did not look like that!
 
Thanks for the quick replies. I've just checked the spindle for end play (longitudinal right?) and there is some movement. Hopefully that's the problem. I'll adjust it tomorrow and let you know whether it solves the problem.

I'm seriously hoping the bearings don't need changing out as Leblond have just told me they neither stock the parts anymore (understandable) or even possess the drawings or specifications. Fingers crossed for the end play adjustment!
 
If turning between centers, I would think so per the picture, be sure to check the tail stock clamp. If the ram was loose it will do the same as the spindle as well, though more likely at the tail stock end vs the whole part.
Pierre
 
Thanks again for all the replies. In answer to the questions: I was holding the work with a self-centering three jaw chuck and a live centre on the tail stock. The tail stock was solidly clamped. The work has a 1 inch diameter with six inches length between the chuck and tail stock. The chatter occurs along the length of the work, but the distance/amplitude of the chatter varies across the length.

There is end play which I feel sure is one problem (hopefully the only one!), but I've temporally been thwarted by a hex grub screw on the adjustment nut that I don't have a correctly sized key for (I'll remedy that at the hardware shop tomorrow). Much worse than this; the second hex grub screw on the adjustment nut has been partially drilled out. I’ll be able to get this fix this with a helicoil, but it will take a little longer.

I'll let you know how I get on. Thanks again for your suggestions.

Pete
 
Fortunately bearing are readilly available from just about any good auto parts stores around. AZ and Discount not so much, but Napa would be a good bet. Bearings are generally off the shelf and the catings and shafts machine to fit. You'l have to yank it apart abnd drift out the old bearings and take them to be matched. We have a place in Gainesville called Bearings and drives and they specialize in that stuff. I have never looked for a bearing they didn't either have in stock or get within 24 hours. Hope this helps.
Bob
 
Hello All,

End play adjusted, but the problem (although less so) still persists. I tied continually pumping oil into the front spindle bearing whilst working at it did impact the severity of the chatter, so I'm guessing the problem lies there. Strange that everything feels so solid but hey.

I'll do they best I can to finish my current project (a jig to hold bicycle chainstays for mitering) and then rebuilding/restoring the lathe will be my next one. Thanks for the bearing suggestion Bob. I'll strip it down and try and match them up.

Thanks all,

Pete
 
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