Thanks for the replies!
I had that same problem before I switched to turning between centers.I got some of the bushings from John at Penturners Products,a carbide tipped dead center and the shorter tool rest also from there and it works great.
I wish I'd done that from the start.
Steve
Couple questions. 1) I'm assuming you do the upper and lower barrels separate. Is that correct? 2) Is carbide tipped a requirement or does that simply help it last longer?
Do you use a mandrel? I've bent one, made everything go wonky. I started using a mandrel saver as well, takes the pressure off my mandrel and keeps me from bowing it when I tighten the tail stock
+1 on the mandrel saver. I use one and they work great. I also use an adjustable mandrel that I can shorten up for shorter pen blanks.
Is the entire pen out of round or only in the middle or the ends? Is it worse on the headstock or tail stock end? SInce it happens over different bushing sets I would guess a mandrel problem (bent, too much pressure on the end) or a misalignment with the lathe itself.
Added later; Take the mandrel and unscrew it from the taper. Lay it on a FLAT SURFACE and roll it. Any bends will be apparent. Take the mandrel and put it in the headstock. Bring the tail stock up to but not touching the mandrel. Spin the lathe by hand and watch for any sideways or up-and-down movement of the mandrel. The mandrel should spin but not move otherwise.
I do currently use a mandrel. It's an adjustable one with a headstock collet. I just took the shaft out and verified that it is perfectly straight by rolling it on my cast iron table saw top as well as against my lee valley machined aluminum straight edge.
I shot a short video that shows the tailstock end as I turn the spindle by hand. You can plainly see there is something wrong.
Pen Mandrel Problem - YouTube
I'm no expert, but I'm guessing this is likely gunk in the headstock taper or on the mandrel taper. They feel clean, but I do see surface discoloration. (Damn you Memphis humidity!)
It's a bit difficult to tell where along the barrels the problem is occurring because it's not consistent from pen to pen.
I just turned a cigar pen and noticed a couple of things. In this case, it appears as though the turned barrels are just fine. They're the right diameter and everything aligns properly once pressed together. Before removing the barrels from the mandrel I was puzzled to see that the blanks and the bushing didn't align... like this (exaggerated of course):
Also, I've found that if the ends of your blanks aren't truly square, you'll get runout.
Paul; First, the blank ends have to be square with the brass tube, not the blank.
I don't think that's my problem, but I will be careful with that in the future.
One method I use is to turn the blank(s) just down to round. Don't size them yet. Change the lathe speed to low speed, turn it on and lay a turning tool shaft on the bushing. If you feel any vibration, the outer dimension of the bushing isn't rotating concentrically. Stop and check to see where that vibration is coming from before continuing to turn.
BE CAREFUL when doing this not to touch the blank. I am not responsible if you hurt yourself. Not everyone is as obsessively safety conscious as I try to be.
I have certainly noticed this. I'm guessing it's either the inside and outside of the bushings not being concentric (see graphic above), the mandrel not spinning true, or a combination of both.
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Again, thanks for all the responses! I hope what I have added in this response will help lead to a resolution.
