Out of Round

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jack barnes

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I need ideas on what is the problem I'm having. On the last few pens I've turned the nibs are proud on one side. I use calipers,it's not the bushing because it's different pens. I use a beall collect chuck replaced the mandral shaft, live center, checked the head and tail stock with a dial indiacator. No the wife will not go for me buying a new lathe, so I could use the help.

Jack
 
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Good point, Gary.

Mandrel and bushings from different suppliers?

(Boy, I am getting my post count up on this one!!!)[}:)][}:)][}:)]
 
Hi Jack, What I do on all my pens is when I get close to the bushings, I rotate the blanks 180 degrees, this seems to help quite a bit. I know that jsut treats the symptom, but what the heck. I have never had Gary's problem (I don't think), but Ed's suggestion of cleaning out the mandrel hole is a good one. I think that's probably a major cause.
Good luck, you'll figure it out.
 
I just tossed a set of 7mm bushings that had a oversized ID.
Heck I like never figured out what was going on. When you are dealing with Made in China one must look very close.
 
How do you square your blanks? I am one that tends to believe the off center issue comes from some face not true, either bushing or blank. I think over thightening the nut can cause issues depending on the type of wood, because the bushing tightens mostly on the wood, and not the end of the tube. I fyou are using bushings that have a smaller diameter that slips into the tube, if there is much size difference there could also cause the tubes to run off-center.
 
I'm sorry for not responding sooner. I had replaced the mandrel rod, and I rotate the blanks 180 degrees. I don't normaly turn the nib end at the headstock, gave that a try nib end seems ok, now clip end is out. I know that I'm not over tighting the nut or using to much pressure during turning. I use a barrel trimer. I never checked the bushings to see if they are lose on the rod will check that.

Thanks you all
Jack
 
I agree with loose fitting bushings especially when there are four bushings are a major problem. The two halves will tighten up misaligned and then out of round on the parts away from the headstock.
 
A lot of the out-of-roundness is caused by sanding. The wood grain changes on different sides of the pen barrel, and the different grain sands away at a different rate. The flat grain will sand away a lot faster than the edge grain, and sanding the spinning pen barrel will make it into an oval shape.

The solution:
Learn to make a smoother cut with the turning tools so less sanding is required and you can start sanding at a finer grit.
 
I think Gary had it right for many of these problems. Except for 7mm pens, I now use the 'no mandrel' method exclusively. And even with the 7mm's I do final sanding and finishing with no mandrel. Getting rid of that whip and chatter makes an amazing difference. As for different suppliers of mandrels and bushings. Don't think about it, you'll go crazy trying to sort those out. Many suppliers buy from other sources and, for the most part, you don't know who made what unless he's on first with who. But do check for loosness of bushing on mandrel, it will, at least, give a clue to where sloppiness is, or might be, coming from.
 
Originally posted by mikes pens
<br />I absolutely 110% agree with Russ!
Click to expand...

Same here. I always make sure to shape with the skew as far as possible to avoid this problem. Its amazing how grain can cause an unplanned shift when you are creating spiral-cut pens as well.
 
Just to let you know, Lee Valley tools does sell a morse taper clean out tool to help keep those tapered holes nice and clean. I don't have one myself, but just thought I would pass it on.

Sheldon
 
I've taken care of my out-of-roundness problems by turning without a mandrel. I picked up a MT2 dead center and the popular live center from Little Machine Shop. I turn each pen segment separately using the holes of the bushings and have eliminated the problem. It takes a bit longer now that I turn and finish each segment individually.

Gary
Sacramento, California

(Heading to Provo!)
 
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