What the...?!?

[Jon Nutting]

I've been turning a bunch of pens as Christmas gifts and have had several instances of uneven material around the tubes. Ive mostly taken care of it with light touch ups and sanding but its still lopsided to some degree. I wasn't sure if I had a wobble on my lathe or if my bushings were just worn but I bought some new bushings and still had it happen so rules that out. I'm at a loss at this point. I'm using a jet 1221vs...thoughts?

 

[Dalecamino]

If you are using bushings on a mandrel, you may have the thumb nut over tightened. This will actually cause the mandrel to bend, causing what is called out of round (OOR) There is a certain spot in snugness with this thumb nut. That is, too loose, the blank will stop turning when you touch the turning tool. Too tight, the mandrel bends. Best solution is turning between center bushings (B2B) , that eliminates the use of a mandrel. Some of our vendors supply these bushings.

 

[Jon Nutting]

Thanks, I forgot to specify. I'm using a mandrel with a mandrel saver in the tail stock. I'm relatively new to pen turning so ill do some googling on your suggestion. Thanks!

 

[qquake]

There is obviously a wobble somewhere, I'm guessing in the headstock. Believe it or not, it could be as simple as a dirty Morse taper. It's happened to me. Try cleaning all the internal and external surfaces of both tapers with a little solvent and see if that helps. By the way, which mandrel system are you using?

 

[qquake]

Of course, it could be the mandrel system itself. I've used two different ones from PSI, and one from Woodcraft. I recently switched to a cheap collet chuck from Amazon, and it actually seems to be more accurate.

#2 Morse Taper Maxi-Mandrel

#2 Morse Taper Maxi-Mandrel#2 Morse Taper Maxi-Mandrel - This new mandrel features a 7mm mandrel shaft that slides through a headstock collet. This feature guarantees a perfectly concentric pen. The mandrel easily adapts to different length projects. Simply mount your tubes and bushings then slid

www.pennstateind.com

#2 Morse Taper Keyless Pen Mandrel System

The quickest and most convenient pen mandrel on the market. The keyless feature allows you to instantly hand loosen and tighten a collet that secures the 7mm mandrel shaft. Plus you can quickly slide and lock the shaft so you get the exact length of your turning and a guaranteed perfectly concentr

www.pennstateind.com

Whiteside Pro Pen Mandrel #2 MT | Woodcraft

Buy the Pro Pen Mandrel #2 MT for sale online from Woodcraft. Visit us to order online or find your local Woodcraft store today!

www.woodcraft.com

 

[EricRN]

There is obviously a wobble somewhere, I'm guessing in the headstock. Believe it or not, it could be as simple as a dirty Morse taper. It's happened to me. Try cleaning all the internal and external surfaces of both tapers with a little solvent and see if that helps. By the way, which mandrel system are you using?

Yup--This happened to me too. Small piece of swarf got stuck in the taper and caused all my pens to be slightly off. If you sand longitudinally and radially, I've also oversanded longitudinally before causing the pen to be off center. Finally, if you are using kits that have pieces that thread-onto delicate threads (like a finial), don't press directly on the threads when assembling the pen. Either screw the finial on and press it in as one unit, or use a slightly oversized tube to press on the area outside the threads, if that makes sense.

Finally, I've just had mandrels get out of whack even with a mandrel saver. So you might test that your mandrel is running true with a dial indicator and, if not, replace it and don't tighten it down so tight.

 

[Mortalis]

If you are using bushings on a mandrel, you may have the thumb nut over tightened. This will actually cause the mandrel to bend, causing what is called out of round (OOR) There is a certain spot in snugness with this thumb nut. That is, too loose, the blank will stop turning when you touch the turning tool. Too tight, the mandrel bends. Best solution is turning between center bushings (B2B) , that eliminates the use of a mandrel. Some of our vendors supply these bushings.

IMO the mandrel bending is actually caused by the tail stock and a live center in the end of the mandrel and the tail stock is too tight. The thumb screw will tighten the bushings to the blank and does not alter the mandrel. This will also show up if the blanks are not square to the tubes.
Since the OP is using a mandrel saver the mandrel should not be bending. I would say the ends of the blank are not perfectly square or there is build up of CA glue or the Morse taper is not fitting properly.

 

[leehljp]

https://www.penturners.org/search/46688/?q=Mandrel+saver&o=relevance

TWO excellent mandrel savers manufactured with very tight tolerances: Woodpecker and Whiteside. Woodpecker has a fine finish too; Whiteside is just manufactured with industrial standards that high quality industrial needs expects (No bling).

Eliminating the most fittings eliminates the most problems - TBC (Look up / Search "TBC")

 

[RobS]

I have a 1221vs, I have discovered that if the lathe is not on a flat even surface, the slight bow in the table will translate to deflection and bow in my pens. You would not think it would, but the minute I put it on a true flat surface that problem went away.

However, the mandrel saver I used had some play in it, and although it turns true, I have to lightly sand the tailstock end of the turned barrel, its not the smooth finish i get on the head side, when I'm turning acrylic acetate or alumilite

 

[magpens]

I agree with Hank above.

Learn to do your turning with TBC ..... Turning Between Centers ..... doing things this way GREATLY IMPROVED my results !

 

[Paul in OKC]

also how do you square the ends?

 

[Dalecamino]

IMO the mandrel bending is actually caused by the tail stock and a live center in the end of the mandrel and the tail stock is too tight. The thumb screw will tighten the bushings to the blank and does not alter the mandrel. This will also show up if the blanks are not square to the tubes.
Since the OP is using a mandrel saver the mandrel should not be bending. I would say the ends of the blank are not perfectly square or there is build up of CA glue or the Morse taper is not fitting properly.

Are you telling me I'm wrong?

 

[leehljp]

IMO the mandrel bending is actually caused by the tail stock and a live center in the end of the mandrel and the tail stock is too tight. The thumb screw will tighten the bushings to the blank and does not alter the mandrel. This will also show up if the blanks are not square to the tubes.
Since the OP is using a mandrel saver the mandrel should not be bending. I would say the ends of the blank are not perfectly square or there is build up of CA glue or the Morse taper is not fitting properly.

There was a discussion along this line a few weeks ago and the conclusion was, in general, those with the higher quality (and price) mandrel savers had less problems. This is what we ran into back 10 -12 years ago between commercial bushings vs custom made (Quality close tolerance) bushings. Play, slop, wiggle in bushings and mandrel savers lead to similar problems. Over tightening a mandrel nut to an unsquared blank end can cause mandrel stress and force it to bend when centrifugal forces come into play.

 

[Dalecamino]

Hank, I believe that discussion 10-12 years ago is where I got my information from. Before switching to B2B bushings from John Goodin, I tried backing off the thumb nut a bit, and it solved my problem. I know nothing about mandrel savers, because I've never owned one. Thanks for the reminder.

 

[Dalecamino]

Jon, here is a link to a site that makes TBC (Turning Between Centers) bushings I referred to. You put a dead center in the head stock, and a live center in the tail stock. The bushings go in each end of your blank, and mounted between the centers.

TBCBushings.com

Turn between center bushings for pen turners

www.tbcbushings.com

 

[Jon Nutting]

Jon, here is a link to a site that makes TBC (Turning Between Centers) bushings I referred to. You put a dead center in the head stock, and a live center in the tail stock. The bushings go in each end of your blank, and mounted between the centers.

TBCBushings.com

Turn between center bushings for pen turners

www.tbcbushings.com

Thanks Dale!