Pen Barrels Turned out of round--Help

[Doug M Jones]

I am turning pens for my confirmation students at church and the first one I did the barrel was out of round. I have turned about 10 pens before this and never had this problem. What have I done and how can I fix it. I have to have these done by Sunday.

Thanks for your help

[Ken Fitzgerald]

Doug.......A couple of things I'd check.....1st. is your mandrel no longer straight? A crooked mandrel would cause it. 2nd. If your mandrel is straight, could you have had too much pressure on it when you were using it causing it to flex? 3rd. Make sure the points on you drive center and live center still align...If they don't check for dirt, chips in the morse taper etc..... I"m sure other turners will chime in shortly.

[Brodie Brickey]

Doug,

I think Ken has covered the main possibilities. Give those a spin so to speak and let us know.

[Jeffrey Fusaro]

when you have the bushings and pen blanks on the mandrel shaft, make sure that the last bushing (closest to the tail stock) is fully seated on the mandrel rod and not resting on the threads. if the bushing is partially resting on the threads, this allows the end bushing and blank to move and will result in a poor fit with the pen components.

i learned that one the hard way...

[Jonathon Spafford]

Check this out... Russ Fairfield has some helpful hints about straightning a mandrel! http://www.woodturnerruss.com/Pen12a.html

[Jonathon Spafford]

when you have the bushings and pen blanks on the mandrel shaft, make sure that the last bushing (closest to the tail stock) is fully seated on the mandrel rod and not resting on the threads. if the bushing is partially resting on the threads, this allows the end bushing and blank to move and will result in a poor fit with the pen components.

i learned that one the hard way...

I'm curious... why does having a bushing on the threads put the tube out of wack? If you don't have a bushing partly on the threads you can't tighten it down all the way! I have had pens out of round and I usually have a bushing resting on the threads, but I can't figure out why this would affect it!

[Grant Wilkinson]

Doug

I hope this doesn't sound to obvious, but have you checked the inside diameter of your bushings against the diameter of your mandrel? The only time that I had your problem was when I used an A mandrel with bushings that needed a B mandrel. There was no slop when I was turning the blank because the holder was tight enough, but since the mandrel was not in the dead centre of the bushings, I produced an out of round pen.

[Doug M Jones]

One thing I forgot to mention is that the offending "Pen" was really a pencil and I have made several of the matching pen but this was the first pencil. It takes different smaller bushings and although it is supposed to be an 8MM tube, it will not let the 8MM bore on the pen mill through. Slightly small than the Pen tube.

I'll have to try some of the suggestions tonight for round two.

Thanks again for all the good advice I get from this forum.

[Joe Melton]

There was a problem with the bushings on one kit a few months ago in that they were not concentric. If you have calipers, you might check that as it could have happened with yours, too.
Consider, also, that mandrels are very cheaply made and it isn't really reasonable to expect them to turn perfectly. I often find brand new ones that are terrible and consider myself lucky if I buy one that turns true.
As you use a mandrel, it will start to deform due to pressure exerting during turning. I consider them disposables, like bushings, and due for periodic replacement.
Lastly, I always loosen the nut and rotate the pen blanks between sanding grits. This minimizes the oblateness. Of course, when I turn the blanks, I hold the bushings in place so they don't also rotate.
Hope this helps.
Joe

[Doug M Jones]

I changed mandrels and that seems to have fixed my problem. Fortunately I had a spare. I must have been either putting too much force on the blank when cutting or tightening up the tailstock too much but the mandrel was bowed. With replacement stems at about $5-$6 is it worth the effort to try to straighten it? I know very little about woodworking and even less about metal working.

Thanks for all the good advice. It's great to have a place to come to with so many that have "been there"

[Jeffrey Fusaro]

I'm curious... why does having a bushing on the threads put the tube out of wack? If you don't have a bushing partly on the threads you can't tighten it down all the way! I have had pens out of round and I usually have a bushing resting on the threads, but I can't figure out why this would affect it!


jonathon--

while turning the last batch of pens, i had one brass tube/wooden barrel that was slightly off center when i inspected it after turning (the brass tube and wood were not concentric).

when i looked at my mandrel set-up, i noticed that the tail stock end bushing was over the threaded portion of the mandrel rod, instead of resting on the smooth/machined portion of the rod. being that the threads have a smaller outside diameter than the machined rod surface, i attributed the non-concentric result to be caused by my not having the last bushing in the correct place on the mandrel rod.

i usually try to place the last bushing on the manrel rod such that about 1mm of the threaded portion is still inside the bushing. this allows me to sufficiently tighten the set up.

it's too early in the morning. i haven't finished my first cup of coffee. i hope this makes some sense... :rolleyes:

[Jonathon Spafford]

it's too early in the morning. i haven't finished my first cup of coffee. i hope this makes some sense... :rolleyes:

Got it! Makes sense.... it is really tricky because there are so many little things in pen turnings that can lead to minute inaccuracies that when all added up can really throw the barrel centering off! I'll have to make sure that I don't do this next time I turn a pen!