Turned blanks not centered

[DavidDFW]

I dont know if this is a common starter problem or not, but I have had a run of pens now where my pens end up off center after Ive turned it. Not sure how to describe it, but I end up with a portion of the pen below the bushing with the other side (same end of the pen) flush with the bushing. Anyone have a thought as to what Im doing wrong? Its confusing to me as it seems that the whole thing would be below, not just part of it.

Said another way, once Ive completed turning the pen, the tube isnt centered, and the wood is thinner on one side than the other.

Thanks in advance for any thoughts.

 

[Tn-Steve]

That's the classic OOR (Out-Of-Round) problem. Ultimate solution, go to what is called "Mandrel Less" or "Center To Center" turning. (Lots of good posts on those subjects).

The usual suspects in this are running the tail-stock in too tight, not having the mandrel centered to start with, or too much pressure while turning. My technique is to put the mandrel in the head stock, but leave the brass disk loose at first. Rotate it a few times by hand with the end of the tail stock just off the end of the mandrel. If it looks like it's pretty well centered, keep turning the headstock by hand, and slowly turn in the live center until it turns along with the mandrel. STOP.... Don't crank it in another little bit, really, it's not needed. Now you can tighten up the brass wheel, again, just tight enough to keep the blanks from rotating when you turn them. I actually check it a few times, I need it tighter for roughing them out, then once it gets round I can usually ease off the tension a touch.

Don't use too much pressure, that will tend to make the mandrel flex.

It's also possible that you have some bushings that are OOR to start with. It's not unheard of by any means. There are some good folks here who I'm sure will offer more and better suggestions, but if you don't over-pressure things it will probably go a long way to help with the problem.

BTW, Mandrels are cheap, I HIGHLY recommend getting a few extras for the bench. Many of us here have managed to turn on the lathe without getting the tailstock up against the end of the mandrel, and it tends to get real "Exciting" then.

One Last Thing (as Columbo would say), are you using a true 60 degree live center in your tail-stock, or is it the multi-purpose one that came with the lathe. Those aren't a true 60 Degrees, and can allow the end of the mandrel to move a bit as you turn.

Hope this helps,

Steve

 

[wb7whi]

Steve pretty much covered it. I routinely check my mandrils bevore putting on the blanks. Bring the tail stock up until it is nearly touching the end of the mandril to act as a reference. Turn the mandril by hand to see if there is any wobble and if so gently bend the mandril until it is running true. Then, like Steve said, load the blanks and check to see if the system still turns true.

 

[jttheclockman]

Another little trick I learned from Barry Gross is when you get really close to the final passes, stop the lathe and loosen the brass nut and rotate the blanks 90 degrees on the mandrel. Lightly tighten the nut and finish the passes. Works, try it.

 

[willardz]

This happened when I first started, ended up buying a new mandrel, the other was bent from me tightening it too much. The mandrels are pretty inexpensive to replace. If all else fails buy a new mandrel.

 

[DavidDFW]

thanks for the thoughts... I checked the mandrel against the tail stock and it looked like it was running true, but I definitely press the tailstock into the mandrel a lot harder than you guys are suggesting. Sounds like I might need a different live center and a new mandrel

 

[Manny]

The adjustable mandrel is nice. I would suggest at the very minimum that you turn one blank at a time with a shortened adjustable mandrel. going mandreless will be your next step anyway. go to Johnnycnc's web site and buy the center and the bushing and your problem is gone...... Unless you're centers are not aligned. Nothing will help you then until thats fixed.


Manny

 

[leehljp]

David,

I started posting a link to a PDF file to new members in February. At the bottom is a mention of the 60° center needed for mandrels. Also in the PDF file is a light overview of many aspects of pen turning as it relates to pens, finishes, tools, and methods. I don't think this was posted at the time you joined so here it the link.

http://www.penturners.org/forum/showthread.php?t=42446

 

[advdiver]

I too had this problem. After reading numerous posts I found that the live center I was using was not meant to be used on a metal mandrel. The end of the mandrel is coned shaped at 60 degrees. Ordered a 60 degree live center and no more porblems.

Gerry

 

[leehljp]

I too had this problem. After reading numerous posts I found that the live center I was using was not meant to be used on a metal mandrel. The end of the mandrel is coned shaped at 60 degrees. Ordered a 60 degree live center and no more porblems.

Gerry

Gerry,

Welcome! In the post above yours in a link that is helpful for many of the common situations pen turners find themselves in. Hope it helps. Post some picts of your work!

 

[advdiver]

Hank, As you can see I joined the IAP back in Sept and that was my first post. I have used yours and well as other members suggestions and have learned a great deal. Thanks to all for opening my eyes to the wonderful world of turning. I will indeed post pictures of my work. But remember my work may be the direct result of yours and other members previous posts.

Gerry

 

[aldwardo]

That's the classic OOR (Out-Of-Round) problem. Ultimate solution, go to what is called "Mandrel Less" or "Center To Center" turning. (Lots of good posts on those subjects).

The usual suspects in this are running the tail-stock in too tight, not having the mandrel centered to start with, or too much pressure while turning. My technique is to put the mandrel in the head stock, but leave the brass disk loose at first. Rotate it a few times by hand with the end of the tail stock just off the end of the mandrel. If it looks like it's pretty well centered, keep turning the headstock by hand, and slowly turn in the live center until it turns along with the mandrel. STOP.... Don't crank it in another little bit, really, it's not needed. Now you can tighten up the brass wheel, again, just tight enough to keep the blanks from rotating when you turn them. I actually check it a few times, I need it tighter for roughing them out, then once it gets round I can usually ease off the tension a touch.

Don't use too much pressure, that will tend to make the mandrel flex.

It's also possible that you have some bushings that are OOR to start with. It's not unheard of by any means. There are some good folks here who I'm sure will offer more and better suggestions, but if you don't over-pressure things it will probably go a long way to help with the problem.

BTW, Mandrels are cheap, I HIGHLY recommend getting a few extras for the bench. Many of us here have managed to turn on the lathe without getting the tailstock up against the end of the mandrel, and it tends to get real "Exciting" then.

One Last Thing (as Columbo would say), are you using a true 60 degree live center in your tail-stock, or is it the multi-purpose one that came with the lathe. Those aren't a true 60 Degrees, and can allow the end of the mandrel to move a bit as you turn.

Hope this helps,

Steve

Thank you very much for that. I have only turned three pens, but I had this problem on two of them and was getting frustrated. Turns out I was tightening the tailstock way too tight. Thanks!

 

[Shelt71]

All,
Thanks so much for this info. I just started turning pens about 2 months ago, and have been having this "oor" problem. All this great info,(especially the 60Deg live center) will deffiently help improve my pens. Thanks so much! This site is awesome by the way, stumbled upon it yesterday, and already learned a ton of pointers!

 

[RussFairfield]

Too much pressure on the tailstock is a common problem. If can bend the mandrel, and that means the blanks will not be on the same center line as the brass tubes at the middle of the mandrel. You only need enough pressure that the tail-center spins with the mandrel, and no more. You are not trying to drive the mandrel out the other end of the lathe.