off-center barrels

[Penburst]

I just finished a Doctor Sing pen from CSU and find the upper and lower parts are misaligned.
The bushings are truly round and centered and my mandrel is straight. What could be wrong? I need to resolve this as I have five more to make. Thanks in advance.
Bob M.

 

[Charlie_W]

Can you add a close up pic?

I assume you are turning both blanks together at once on the same mandrel.
Can you turn only one piece at a time? is it an adjustable mandrel?

You might want to try using the bushings/mandrel to get the pen blank close to size one blank at a time and then going strictly between centers for the final sizing...one blank at a time.
I think the problem is most likely mandrel/bushing related. Also, make sure the ends of the blanks are square with the tube.

Hope this helps.

 

[terry q]

You could be tightening the brass nut too much and bending the mandrel. DAMHIKT

 

[Penburst]

Thank you both. I'll try your ideas in several days when I can get back to this.
Bob M.

 

[kingkeyman]

I've found that a little glue on one side of the inner tube wall will cause that as well.

 

[Penburst]

Good point! I'll look into that also. Thanks.

 

[Penburst]

Problem solved? I now use a barrel trimmer to be sure the blank is square to the tube. I turn only one blank of the two at a time to minimize any chance of a slight wobble from the mandrel. To avoid possibly bending the mandrel, I've been using a "mandrel saver" to put tightening pressure on the blank and not on the mandrel. With 4 pens done, I can say so far, so good.

 

[JasonC]

Problem solved? I now use a barrel trimmer to be sure the blank is square to the tube. I turn only one blank of the two at a time to minimize any chance of a slight wobble from the mandrel. To avoid possibly bending the mandrel, I've been using a "mandrel saver" to put tightening pressure on the blank and not on the mandrel. With 4 pens done, I can say so far, so good.

What live center were you using with the mandrel? 60 degree or the one that came with the lathe with a narrower taper?

 

[Penburst]

I'm not using a live center. The mandrel saver avoids use of a traditional live center.

 

[JasonC]

Well aware of that.

Prior to mentioning use of the mandrel saver you had issues so I asked which live center you were using.

I can only offer help based on info given.