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Turnings coming out oval shaped

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Forum topic by JADobson posted 12-25-2013 05:47 PM 899 views 0 times favorited 18 replies Add to Favorites Watch
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JADobson

370 posts in 831 days


12-25-2013 05:47 PM

Topic tags/keywords: oval pen turning

So I turned a pen for a Christmas present and once I put it together I noticed a problem. Here is the photo:

As you can see the wood is not flush with hardware. When it was on the lathe it matched the bushings perfectly and it matches the hardware on the opposite side of the pen perfectly. It appears that the blank is being turned in an oval shape so that one side matches the hardware and the other is elongated. Any ideas how or why this might be happening? It only happened on one of the blanks, the other one turned out just fine. Any help is appreciated. Here is the whole pen:
Click for details

-- James


18 replies so far

View bondogaposis's profile

bondogaposis

2689 posts in 1072 days


#1 posted 12-25-2013 06:47 PM

The wood you used must not have been completely dry. Because wood shrinks about twice as much in the tangential direction than in the radial direction round turnings will dry somewhat oval.

-- Bondo Gaposis

View Jesse.R's profile

Jesse.R

50 posts in 1646 days


#2 posted 12-25-2013 06:52 PM

your pen mandril could be bent. happened to me once with the 7mm pens same result.

-- jesse

View Dark_Lightning's profile

Dark_Lightning

1796 posts in 1829 days


#3 posted 12-25-2013 09:43 PM

You can bow the mandrel slightly if you clamp it too tightly in the lathe. I can spring back, or may stay bowed. Roll it on a flat surface to check for bending.

View Rick M.'s profile

Rick M.

4327 posts in 1100 days


#4 posted 12-26-2013 04:42 AM

I agree with Bondo, it lost moisture and went oval.

-- http://thewoodknack.blogspot.com/

View Marcus's profile

Marcus

1077 posts in 740 days


#5 posted 12-26-2013 01:34 PM

I would guess Bent mandrel based on my experience as well.

View Rick M.'s profile

Rick M.

4327 posts in 1100 days


#6 posted 12-26-2013 06:18 PM

If you bend the mandrel wouldn’t it be lopsided like an off center turning?

-- http://thewoodknack.blogspot.com/

View WibblyPig's profile

WibblyPig

168 posts in 1995 days


#7 posted 12-26-2013 08:40 PM

You may have tightened you mandrel too much. One way to check is after you finish turning, loosen it a bit and turn the bushings 90 degrees or so. Does everything still line up? If so, then you should be good.

What did you finish it with? If something water-based; WTF or the like, one side may have absorbed more than the other.

My newest favorite is turning between centers. All you need is a live center and a dead center. You turn one side at a time and you don’t have to worry about mandrels, over-tightening, etc.

-- Steve, Webster Groves, MO "A society grows great when old men plant trees whose shade they know they shall never sit in."

View Wildwood's profile

Wildwood

1172 posts in 855 days


#8 posted 12-26-2013 10:24 PM

Several things can contribute to out of round pen barrels pretty much up to you to figure it out and correct.

Bent Mandrel
Over tightening tailstock, or mandrel nut
Bad bushings or pen tubes not fitting squarely or too loose on bushings
Head/tailstock not aligned
Run out at headstock, bushings on mandrel
Pushing too hard while turning with dull tools

-- Bill

View Drew224's profile

Drew224

25 posts in 1043 days


#9 posted 12-27-2013 03:54 AM

[quote]

Several things can contribute to out of round pen barrels pretty much up to you to figure it out and correct.

Bent Mandrel
Over tightening tailstock, or mandrel nut
Bad bushings or pen tubes not fitting squarely or too loose on bushings
Head/tailstock not aligned
Run out at headstock, bushings on mandrel
Pushing too hard while turning with dull tools

—Bill
[/quote]

I agree with this 100 percent. wood would only crack if it was wet. the biggest culprit is the bent mandrel rod and an over tightened tailstock

-- "...Be sure to read, Understand & follow the manufactures safety rules... And there is never more importaint rule than wearing safety glasses."

View REO's profile

REO

647 posts in 794 days


#10 posted 12-27-2013 04:24 AM

possibly wet wood. bent mandrel is a good possibility. out of line centers can bow the mandrel but the uneven cutting is from flutter that develops from the mandrel being bowed allowing the workpiece to oscillate up and down from cutting pressure. If you set up the mandrel in the headstock does the tailstock engage cleanly with out shifting the barrel of the mandrel to seat?

View JADobson's profile

JADobson

370 posts in 831 days


#11 posted 12-27-2013 05:13 AM

Thanks for all the answers guys. I’m not at home right now so I can’t check anything right now but I think a bent mandrel might be a possibility. For some reason as soon as I turn on the lathe the mandrel comes loose from the morse taper causing the blanks to loosen. To counter this I was clamping down on my tailstock to keep everything tight (it didn’t help). I thought I might try some loc-tite on those threads to keep it from loosening. I don’t think it was wet, I’d had the blank for a year and I got it from a guy who had had it for a long time as well. Dull tools could be a problem too (Wolverine grinding jig for Christmas!!).

-- James

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REO

647 posts in 794 days


#12 posted 12-27-2013 03:29 PM

I wouldn’t use the lock tight on the mandrel that is just a bandied and could cause permanent damage to the threads.

View Underdog's profile

Underdog

552 posts in 756 days


#13 posted 12-27-2013 11:21 PM

I could never get anything perfectly centered on mandrels. There’s too much play between the rod, the bushings and the pen tubes…. (not to mention all the other things that have been mentioned.)

My advice?

Turn with the pen tubes between centers and ditch the mandrels.
Dead center in the headstock and live center in the tailstock.

Go!

View JADobson's profile

JADobson

370 posts in 831 days


#14 posted 12-28-2013 04:34 PM

When you turn between centres do you just use callipers to check for the proper width? Or can you get or need special bushings?

-- James

View lumberjoe's profile

lumberjoe

2847 posts in 969 days


#15 posted 12-28-2013 05:46 PM

Your tubes are loose on the inside. If you have enough play to be able to get thick CA or epoxy on the tubes and not push it all off when inserting in the blank, this will happen. Your blank is perfectly round, the tube isn’t centered.

-- www.etsy.com/shop/KandJWoodCrafts

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