Out of round, off center pen

[Cincinnati]

My pre-teen boys and I have been turning pen kits for a few years. Occasionally we get oval barrels or barrels off center from the tube. I switched from a tapered mandrel to a collet mandrel. Then replaced the rod. I got a few round and concentric barrels. then I let my boys turn and we seem to go back to oval barrels. What is causing this?

My guess was possibly too much pressure on the tail stock causing the mandrel rod to flex. Or bending the rod while loading or unloading the pen parts, bushings, Anne tightening or removing the retaining nut.

How do I correct and prevent this?

 

[Drstrangefart]

I encounter that kind of problem on softer materials. Usually the sanding process digs in deeper on softer parts leaving flat or off areas floating around. One solution is mounting sandpaper on a giant paint stirrer to make a sanding stick, giving you more even pressure. You should be able to look down the length of your mandrel and see if it's bent. Or feel the mandrel while it's turning bare. Making sure the sharpening on your tools is beyond reproach is a good idea, too. I sharpen mine every one or two pens. Also using a more gentle touch while turning and slowing your process down helps out. Hopefully some or all of these will be of help. If you have a cheap, crappy lathe, there's only one fix. A good lathe.

 

[Russell Eaton]

The nut on the mandrel could be too tight. That can cause a oval as well. If you turn between centers it will solve all those problems. There is a good article about that process in the library. Hope this helps.

 

[randyrls]

My guess was possibly too much pressure on the tail stock causing the mandrel rod to flex. Or bending the rod while loading or unloading the pen parts, bushings, Anne tightening or removing the retaining nut.

How do I correct and prevent this?

If the blanks aren't milled off at exactly 90 degrees to the brass tube, tightening the tail stock nut can cause the mandrel rod to bend.

 

[Monty]

You can eliminate the problem buy turning between centers.

 

[GoodTurns]

You can eliminate the problem buy turning between centers.

what he said.

lots of variables can be eliminated when you eliminate the mandrel...overtightening, bent rod, misfit in stock....

 

[philb]

Also make sure the end of your tubes and blank are square. This has caused probably a bigger difference in out-of-round than my mandrel did, when the blanks are squared the out-of-round was less on a mandrel. But still square ends and between centres and your definitely in the right direction!

PHIL

 

[Cincinnati]

Ok. I guess I'm Demonstrating my lack of knowledge in this area. I thought I was turning between centers. Are you saying don't use a mandrel? If you don't, When do you drill out the center hole and insert the tube?

 

[Russell Eaton]

60° live and dead centers. Drill the blank and put the tube in first. Read the Strick in the library. It makes it all clear.

 

[jttheclockman]

To solve the problem don't let the kids touch the tools.:biggrin:

You got all the right answers with many variables listed. Everything from overtightening the retaining nut to a bent mandrel to using too much pressure when turning. In turning especially pens, a light touch is the key words. Turn the nut just tight enough to lock the blank. Turn the tailstock to just tight enough to stop the live center from not spinning. Everyone talk about turning between centers and yes that eliminates variables but is not the end all to all problems by no means and I read this over and over here. You can use a mandrel with no problems just as well if you keep your equipment tuned as well as you need to do with mandreless bushing and such. It will start with getting the blank square. I have many pens with a mandrel and will continue to do so. You may have to look at your techniques and if you bent the mandrel from the start then you will need to start there. Storage of your tools is also important. Gets overlooked. Check all the points made by the others then if all else fails give JohnnyCNC a call and he will set you up with some nice bushings but again will not solve all problems.

 

[ed4copies]

Another opinion: Use the "professional" mandrel and turn only one barrel at a time.

Much harder to bend the mandrel when it is short.

 

[KGPenmaker]

Another opinion: Use the "professional" mandrel and turn only one barrel at a time.

Much harder to bend the mandrel when it is short.

+1 to what Ed said. This is what I do because I found the same thing. I think the kids are hogging off material, bending the mandrel which causes the blanks to oval. I do the same thing, so I only turn one barrel at a time and I have not had an oval barrel since I switched, at least not oval enough to notice. Its a hobby for me, so I don't care if this slows down the process.

Paul

 

[randyrls]

Ok. I guess I'm Demonstrating my lack of knowledge in this area. I thought I was turning between centers. Are you saying don't use a mandrel? If you don't, When do you drill out the center hole and insert the tube?

You prepare the blanks as normal, but you use different bushings, and don't use a mandrel.

Take a look at these videos by JohnnyCNC:
http://www.youtube.com/watch?v=_c--nfxh8og
http://www.youtube.com/watch?v=YX4UU5aIu_A
http://www.youtube.com/watch?v=p6wTnychR1U

 

[lorbay]

On the home page there is a tutorial on the right hand side by texatdurango on turning between centres.

Lin.

 

[fernhills]

Hi, i use a mandrel, Don`t see a reason to change yet. I do one barrel at a time. When you get close to final dimension lighten up on the tail stock some, it doesn`t have to be to tight when it is almost done. That helps. Carl

 

[CHICAGOHAND]

Give Johnny a call and end all your problems for the new year.


http://www.penturnersproducts.com/

 

[mach9]

You can check the straightness of the mandrel by spinning it and SLOWLY bringing a felt tipped marker up to it several places along it's length, which will show you the high spots. Eric Andersen's DVD shows how to tune your mandrel this way. I run into out of round barrels when turning blanks that have hard and soft areas. I'm not set up to turn between centers yet. The last one I ran into, I shortened the mandrel, turned one barrel at a time, resharpened my tool real good after I got the diameter close, and went VERY slow. This helped a lot, but took some time. Good luck and Merry Christmas.

 

[Rmartin]

Turning between centers is not the end all be all. If the lathe is not running true, you can have problems. If your head and tail stock are misaligned, you can have problems. If your bushing has a nick or damaged in some way, you can have problems. Even some woods with knots can cause just the slightest wobble, and you can have problems. Turning between centers can actually magnify problems.

 

[sbwertz]

I use a lot of stone fill in my pens, and I have found if I am turning a softer wood, the pen will sand oval because the stone is harder than the wood. I get the same result with wood with a hard grain line in a softer wood. It will sand the soft part more than the hard part resulting in an out of round barrel.

Perhaps the boys are being more agressive with the sandpaper, or using coarser sandpaper.

 

[ctubbs]

Try putting a pointed center in both the head and tail stocks, brint them to the point where they just touch at the points and look down at the points. If they do not align together, read your manual and make the necessary adjustment. Use a good strong light for this and place something white on the bed for contrast. Once this is aligned, do the same thing from the front. The points must align in the horizontal and vertical plane both or you will always turn oval turnings. DAMHIKT UHK(University of Hard Knocks) All of the above suggestions are good, but if they do not cure the problem, then it might be a misalignment problem. Worked for me YMMV
Charles

 

[KGPenmaker]

Try putting a pointed center in both the head and tail stocks, brint them to the point where they just touch at the points and look down at the points. If they do not align together, read your manual and make the necessary adjustment. Use a good strong light for this and place something white on the bed for contrast. Once this is aligned, do the same thing from the front. The points must align in the horizontal and vertical plane both or you will always turn oval turnings. DAMHIKT UHK(University of Hard Knocks) All of the above suggestions are good, but if they do not cure the problem, then it might be a misalignment problem. Worked for me YMMV
Charles

I disagree. Misalignment should not cause an ovalling of the blanks. It would cause a taper, but should not cause ovalling. Metalturners offset the tailstock to turn tapers all the time, the turned pieces still come out round, but with a taper.

Paul