Out of round fix list

[Elliott]

Hi Everyone,

I have seen many-o-questions about pens turning out of center. After several months turning I have finally licked this problem on my lathe, and though I would put together list of reasons why a pen might not turn true.

I hope this helps someone out there.

Please add to the list if you have something new.

1) Mandrel bent
a. Fix - losen the friction nut.
b. Fix â€" Buy a new one
c. Turn without a mandrel (My Solution)

2) Lathe head and tail stock not lined up
a. Fix â€" I need to put a small shim under a corner of my tail stock (Works like a charm)
b. Buy a better lathe with closer tolerances

3) Pen ends not square.
a. Fix â€" Make a sanding jig for sanding at prefect right angles
b. Fix â€" Invest in a good pen mill (My option)

4) Bushing not tight enough on mandrel
a. Fix â€" Don’t know haven’t had to personally deal with this one since I don’t turn on a mandrel

5) MT not fitting true
a. Fix â€" My lathe is crapy so I had to add a small piece of tape to my MT insert to compensate for the un-even fit. It works, but I need to replace the tape as it wares.

6) Wood grain uneven
a. Never encountered this issue, but heard about it.

7) Bushing not drilled in center
a. Buy new bushings

Well that is all I have â€" may your pens all be round.

- E

 

[Fred]

8) Mandrel Bending
a. Refer to No. 1 in list above
b. Do not over tighten tailstock against end of mandrel.
c. Make sure mandrel taper is absolute fit in head of lathe. No MT2 in a MT1 opening, etc.

9) Uneven roundness of mandrel when turning
a. Clean MT opening of head stock
b. Clean any dirt/rust on MT fitting on mandrel

10) Ensure live center pin fits dimple in mandrel
a. Turn between centers using bushings only
b. Use professional mandrel ... similar to using a collet style system

11) Check turning speeds to see if centrifugal force is excessive
A. Adjust turning speeds down

Anyone have anything else? This is a helpful thread and needs to be maintained until there simply are no more ideas to add.

 

[LostintheWoods]

Buildup of CA on bushing, preventing tube from seating squarely, creating the same problem as blank not being squared.

 

[keithkarl2007]

So i don't know what i'm doing wrong. Just got a new mandrel to replace my bent one. Started to turn a yew slimline this evening and again when it came to sanding i am flush with the bushing on one side and proud the other. I didn't have the tailstock too tight, as when i started to turn the blank stopped. I tightened a little more but not a whole lot. The head and tail stock line up correctly.I trimmed the blanks with a pen mill. Is it really possible the bushings are drilled off centre. Its really starting to get to me now

 

[leehljp]

Restating number 1 in different words but with the same meaning - over tightening the mandrel nut itself causes OOR (out of round), bending, etc. Very similar to over tightening the end stock but still different.

With all kinds of people on this forum approaching the same problem from different points of view, and as a parent of more than one kid, I know that repeating things over and over, in different words each time, is a necessity.

 

[hilltopper46]

6) Wood grain uneven
a. Never encountered this issue, but heard about it.

If this means what I think it means, sharpen your skew. If it still does it, sharpen your skew again. If it still does it, well, you get the idea. Some woods (I've noticed this on stabilized burls, among others) set up a frequency that the skew seems to bounce to if it isn't as sharp as it might be, and it almost acts like a chatter tool.

keithkarl2007 wrote:

So i don't know what i'm doing wrong. Just got a new mandrel to replace my bent one. Started to turn a yew slimline this evening and again when it came to sanding i am flush with the bushing on one side and proud the other. I didn't have the tailstock too tight, as when i started to turn the blank stopped. I tightened a little more but not a whole lot. The head and tail stock line up correctly.I trimmed the blanks with a pen mill. Is it really possible the bushings are drilled off centre. Its really starting to get to me now

To which LostintheWoods replied

Buildup of CA on bushing, preventing tube from seating squarely, creating the same problem as blank not being squared.

I agree wholeheartedly. And, it can be something other than CA. I've had this happen with the wax that I use to plug the end of the tubes when I glue them when I didn't get it cleaned out well enough.

 

[Elliott]

keithkarl2007, the first thing you should do is find out where the problem is. This is how I finally fixed it on my lathe.

Here is the first step I would suggest.

1) Is your lather turning true. To check take the tool rest and put it right close to the smooth part of the MT insert. (not the end of the insert, but the side. Also not where the threads are, but a smooth part)

Turn the lathe wheel with your HAND and see if the space between the tool rest and the MT insert changes. I would suggest a starting space less than 1mm, but enough to let a small amount of light through. If the lathe is off center you should see the space growing and shrinking as you turn it with your hand. [let me know what you find out and we can go to step 2]

- E

 

[keithkarl2007]

Thats exactly what i done both with the bent mandrel and the new one. I done this with the bent one first and kept tapping it til i straightened it. I tried it on the new mandrel before i even used it and it seemed to rise away from the toolrest slightly as i turned it by hand

 

[Larry Gottlieb]

One thing that I have found useful is a dial indicator with a magnetic base. I can check the mandrel and bushings to determine if they are off center. I think that they can be purchased relatively inexpensively.

Larry

 

[Paul in OKC]

If the ID of the bushings is a bit big, they will not run true to the mandrel, they will 'hang down' as things get slid on, and that is the way they tighten up.
As to item #1, I (respectfully) disagree, unless your blank ends or bushing faces are not true, this should not cause the problem. The nut is pulling the mandrel. Think about it like tying a rope to a pole, the tighter you pull, the straighter it gets. That's my theory and I'm stickin' to it!
As I think about it, if you bushings are not contacting the tube on the end, then it is at the whim of the denseness of the grain, which could cause it to tweek a bit, but even still, it takes some slop somewhere else to allow that to happen, I would think.

 

[loglugger]

I am with Paul, IF everything is square the tighter the nut the mandrel will be straighter and stronger.

 

[mikes pens]

Often it can be too much sanding. Some woods have hard and soft spots next to each other. Sand a bit and then go back to the skew, then sand... Don't lean too heavy on the sandpaper. You can check the roundness by touching a pencil line to the wood as the pen blank turns on the lathe. If it is round, the pencil line will be uniform all the way around the blank.

 

[leehljp]

Paul, Bob,

I understand the principle of the rope pulled tighter and it would be true with a mandrel and nut - if everything was "perfect". However everything is not usually perfect. A bushing pushed against a nut that is 89.99 degrees will probably snug up fine and give not problem. But a smidgen too tight and the OORs creep in as things move.

Scenerio number 2 is experiential for me, but there were times when I back the nut off a 1/4 turn, the vibration OOR went away. This happened with longer mandrels and it tells me that it could be a "tension" problems somewhere. The tighter a rope becomes, the change in its harmonic resonance. I am probably missing a dozen laws of physics here and accept correction openly on the subject. I am not the expert on the laws of physics, but I am still trying to make sense of my experiences.

 

[Paul in OKC]

Physics shmysics, we are turning pens here![] I agree, though, that at times I have loosened the nut between some turning and it helped. The comment on the differing wood hardness on opposite sides of the barrel is a good one too. Once the 'soft' side starts down, the only way to really correct it is to cut with the tool again.

 

[Fred]

To test your mandrel try reversing the bushings, re-cut them and see if the uneven portion moves to the other end.

Turn your blank and LEAVE the wood in the same order it is mounted ... then take the entire setup and reverse the order of the wood WITHOUT removing the bushings at all. Just slide the setup off and remount from the other end. Make a new cut.

I would surmise that IF the out of round changes then your problem may come from the way you are moving your body as you turn. Many turners shift weight from foot to foot and others lean back and forth. IF one is not careful the attack angle of the tool changes and the wood is ultimately cut differently. This is really noticeable when using a skew to turn down the wood. My own experience on this line of thought was solved by placing one of those dense foam mats on the cement floor so that I could stand more comfortably. It definitely made a difference especially when I was making extremely fine cuts with my 1" skew.

Just my .02 cents worth. Keep us posted as we all can learn something new from time to time. Oh yea, Good Luck!

 

[Blind_Squirrel]

I had a buddy over to the house last night. He is working on a Baron. I showed him the mandreless method. He decided to give it a try. When he got close to the bushings he discovered that his blank was turning out of round.

The bushings have a bit of play in them allowing the blank to whip. I solved the problem by putting the custom sleeve insert that I use on my pen mill into the blank, putting the blank on a mandrel and having him finish the blank that way.

Looks like I need to make myself some Baron bushings this weekend. [B)]