Lathe is turning a taper

tjb

tjb

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I have an Eissen 1440 lathe that I bought new a little less than two years ago. The machine has not been moved or bumped since initial setup. It's been a great machine, but I've noticed lately it's cutting a taper toward the tailstock end. It became apparent when I needed to turn a piece about a 10" long, using a live center in the tailstock. The taper was about ten thou over the full length. I checked bed alignment - nearly perfect but I tweaked it even further. The resulting change was negligible. I chucked up a piece of 3/4" aluminum and turned about 4" without the tailstock. Taper was still there - actually the relative taper was a little worse, given the shorter section. Next I took a piece of 1-1/4" O1 tool steel that is about 3 feet long and chucked it up with 10" showing through the chuck. I mic'ed the 10" section at various points, and it was uniformly dead-on 1-1/4" throughout - just like tool steel ought to be. Using a high precision indicator and rotating with the jog switch, I took measurements of runout at three positions (see photo below). Here are the results:

At 1-1/4" from chuck jaws - zero - +0.0044" TIR
At 4-1/2" from chuck jaws - zero - +0.0091" TIR
At 9-1/4" from chuck jaws - zero - +0.0160" TIR

Clearly, most if not all of my runout is occurring at the chuck. It is a high quality Bison 6" 3-jaw that I've had for a few years. Never had any apparent issues before now. I'm thinking I need to remove the chuck and give it a thorough cleaning, but thought I'd ask first. Am I missing something? Anything else I should test first with the chuck still in place? (I have a nice 6" 4-jaw that I could mount and check for runout.)

Thanks for any help.

Oh, and please disregard the trash on the lathe. I discovered this issue in the middle of working on a project.

Regards,
Terry

IMG_1781.jpg
 
It seems like you are experiencing two completely different situations; runout in the chuck, and cutting taper, the chuck runout may be addressed by first disassembling and cleaning it out, checking again, and possibly regrinding the jaws. It is possible that misalignment of the tailstock may be causing the taper, or possibly the lathe needs re leveling or alignment by the two collar method.
 
yep , like John says ...
missing info: are you cutting using the tailstock? if you are, have you tried adjusting it to remove the taper?
if you are not using the tailstock, why not? 10" is a length I would use a ts with to support. We don't know how deep a cut you are taking with each cut, cutting force translates to taper with an unsupported stock.. you run the risk when you do use a ts and you have a long piece, the middle may push away from your tool and be wider than the ends.

so more info.

my bad, went back and read it again, you did use a ts... son you have a ts alignment problem, adjust the ts
 
tjb said:
(I have a nice 6" 4-jaw that I could mount and check for runout.)
Click to expand...
Yes that would make an interesting comparison with the scroll chuck.
Do you have any reason to think that the spindle might be out of alignment?
 
It seems like you have an alignment problem; start with re leveling or the two collar method.
 
I'll try to respond to all the above in one post because there is a little bit of overlap.

1. Leveling: I started by checking the leveling on the lathe and it was off very slightly. I adjusted until the difference was gone.

2. Spindle alignment: I NEVER overwork my machines. Can't imagine anything that would have caused spindle misalignment. I could be far more aggressive in both depth of cuts and speed, but I'm not in a hurry. Things are usually pretty uneventful in my shop.

3. Chuck runout: Strikes me that this is a near certainty for at least part of the problem. If that's highly likely, am I right in thinking it would make sense to do that first?

4. Tailstock alignment: I have wondered if that could be a factor. That's the main reason I chucked up the O1 and took measurements without the tailstock attached. Given the results, I'm back to thinking first order of business should be serviced and retested. What are the parameters for determining if jaws need to be reground? That would surprise me. I bought the Bison new and am not even remotely aggressive on how I use it.

5. Two collar method: Just a thought, but haven't I already at least partially addressed that? I'm using precision ground O1 tool steel that mic's to exactly 1.2500" all up and down the 10" section that sticks out from the chuck. And I'm getting results that make it pretty obvious there is an issue. And that's AFTER releveling the bed.

Thanks for any further advice.

Regards
 
benmychree said:
Runout has nothing to do with cutting a taper, it just tells you that the chuck needs attention as discussed before.
Click to expand...
Just saw this post, John. That's exactly what I'm thinking makes sense as the first order of operations. How do I know if there is a need to re-grind the jaws? Again, as in my latest post, that would surprise me given how lightly used the chuck is.

Regards
 
More expert people than me will surely help. But I have to say, don't assume anything. Measure it. If you haven't measured it recently, then you don't know it.
 
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