Off center problem

[siric]

I have been having a problem with peppermill tops and botton not aligning and thought that there was something wrong with my method.

But just to check, I bored a hole in a piece of wood and mounted it on a screw chuck (for bottle stoppers) and turned it. Low and behold the hole and the outside of the cut are not concentric!!

This really has me beaten as when I look at the piece when it is turning the hole looks like it is in the center. I took it off my Jet and mounted it on the PSI and get the exact same result

I have looked at the chuck by itself when it is turning and it is true.

Just can't understand it.

Any help would me MOST appreciated!!!

 

[wyone]

have you tried the same thing with different bits? I had a bit that had just a slight bend in it that I did not notice and it really messed with things

 

[RustySplinters]

Is your tailstock true?

 

[flyitfast]

Check for dust or woodchips inside the tailstock. This can cause the morse taper to be off center.
gordon

 

[Dale Allen]

Some pictures of the screw chuck and how it is mounted to the lathe may help.
Something is really off with that much of a difference.

 

[mredburn]

Do you use a center drill to start the hole. A large long drill bit can start off center and keep going. Have you checked the alignment of the tailstock to the headstock? If your drill is dull on one side or bent it will drill off center.

 

[monophoto]

Back to basics - how was the hole drilled? This was a bottle stopper blank, so presumably the hole had to be threaded so that it would screw onto the mandrel. How was it threaded? And the bottom line - when the blank was mounted on the mandrel, was it flush against the mandrel, or was it angled slightly to one side.

This looks to me like either a drilling problem - the hole wasn't absolutely perpendicular to the face of the blank that it went through - or a threading problem - the threads weren't absolutely concentric with the hole.

 

[toddlajoie]

If you drilled the hole the correct size, and threaded the screw chuck in all the way, then mounted and turned this piece round on the lathe, and that is your results, I don't think that could be blamed on dull, bent or off-centered drilling, as you could have had all of those problems at the same time and the lathe would have corrected them (except if the hole was drilled severely off angle, but that would not cause what you are showing, it would just show the face being not perpendicular to the turned profile...). The ONLY thing I could see at that point is something is seriously off center in your screw chuck, tho at the same time, I can't think of anything I've ever seen on a lathe that would ever had been 1/4 of that far off when turning... I would certainly like to see a photo or 2 of your piece mounted on the lathe...

If instead, you turned it round and then drilled the hole, then the issues with dull bits, bent bits, long bits, etc would certainly come into play.

 

[KenV]

Do you use a commercial stopper chuck like the one built for Ruth Niles -- or is this a shop built screw chuck?

Have seen several shop built screw chucks that were not concentric. They consistently produced multi axis turnings -- when multi axis turning were not being sought.

 

[siric]

Ok,

Here are the steps I took -

Cut the blank and drilled it on the drill press. Tapped the hole and screwed on to the chuck. I do not use the tailstock.

monophoto - I looked back at the another piece of the blank and it turns out that it was not perfectly perpendicular - that may be the problem.

Will try again tomorrow and let you know.

Thanks for all of the responses; I was quite perplexed.