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Probably a simple answer... (Read 815 times)
Andy Mauger
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Probably a simple answer...
Aug 7th, 2016 at 10:29am
 
Hi all,

Been getting myself confused over the last couple of days: Decided that I wanted to do a "box making" session as I had a fair few offcuts/scrap lying around but..

As the pic shows, I am getting an odd "gap" between the lid and base.
I have made sure that both the lid and base have slight "inclines" from outer edge-in and that the lid fits (with no obstruction) inside the base.!

I have this issue with both hard and soft woods, so I am starting to think its my tooling.

Any ideas more than welcome.

Many thanks in advance,

Andy.
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Re: Probably a simple answer...
Reply #1 - Aug 7th, 2016 at 11:02am
 
It may simply be warping.
Set the pieces on a known flat surface and see where the gaps are.
You may just need to let the pieces rest and acclimate to the ambient climate after you cut them (separate the lid from the box).
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robo_hippy
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Re: Probably a simple answer...
Reply #2 - Aug 7th, 2016 at 11:15am
 
It could be wood movement, and/or run out in your lathe. Looks like that box is in the 3 inch diameter range, maybe more. Boxes that size will move more than smaller ones. I always rough turn mine first, and then let them sit a month or six to let the wood adjust, meaning that even if the wood is kiln dried, the inside is usually a bit higher in moisture content, and it will 'adjust' to having mass removed. It looks like the box is turned end grain, which will be more stable, but that will still go oval. Not sure why this one curled up though. I have had hollow forms where the bottom when roughed dead flat will warp convex. Just because I guess.

robo hippy
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Ken Vaughan
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Re: Probably a simple answer...
Reply #3 - Aug 7th, 2016 at 2:41pm
 

Andy,

Aligning the grain between the top and bottom will help keep the identification of the relative wood movement balanced. 

I am used to a "box" having the grain running parallel with the ways of the lathe and the hollowing is end grain cutting.  The end grain of the "box" is at the top and bottom.

Your turning, especially the lid, suggests end grain at the side of the lid.  Something that might be termed "lidded bowl"   and the opening warp is more expected with a lidded bowl.

The wood looks like a Philippine Mahogany labeled wood I see here at the  vendors supplying the marine trade.  I find it soft and a challenge to turn.  I like a tighter grained, more dense wood for end grain boxes, but one uses what they have. 

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Re: Probably a simple answer...
Reply #4 - Aug 7th, 2016 at 3:21pm
 
Ken Vaughan wrote on Aug 7th, 2016 at 2:41pm:
I am used to a "box" having the grain running parallel with the ways of the lathe and the hollowing is end grain cutting.  The end grain of the "box" is at the top and bottom.

Your turning, especially the lid, suggests end grain at the side of the lid.  Something that might be termed "lidded bowl"   and the opening warp is more expected with a lidded bowl.



Not to get caught up in semantics but it's my understanding that the way to determine whether something is a lidded box, lidded bowl, lidded dish or lidded jar is to look at it without the lid to see what it best resembles (regardless of grain direction)
Just my two cents
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Ken Vaughan
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Re: Probably a simple answer...
Reply #5 - Aug 7th, 2016 at 5:58pm
 

Andy, the classic Ray Key style end grain boxes never get the gaps because the wood movement is very small along the grain and quite uniform as compared to movement across the grain. 

Bonnie Klein turned green holly to grain matched ends consistently.  She did acknowledge that the end grain boxes moved and could bind.  They moved laterally as she turned and one can hear the change. 

Turning side grain, design the joint so that the movement is less obvious.

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Andy Mauger
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Re: Probably a simple answer...
Reply #6 - Aug 9th, 2016 at 4:46am
 
Hi,

Many thanks for the replies..

Well, I have tried both end and side grain with the same results: Mini gap on opposite sides.! Even tried a simple (very simple) test piece with some old wood which must have been about 5+ years old: Same thing.

However: Cleaned my old CL2 yesterday and found that the main spindle was indeed loose-ish, so that has been tightened and seems to have helped a bit.

It doesn't help that my CL2 is a swivel head lathe that never seems to be lined-up exactly between centres no matter what I do..

Anyway, more trial and error Smiley

Again, many thanks.

Andy.
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Re: Probably a simple answer...
Reply #7 - Aug 9th, 2016 at 7:55am
 
Curious, if you rotate the top 90 degrees does the gap go away?  And if you rest the piece without a tenon on a known flat surface, is there any gap?
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Andy Mauger
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Re: Probably a simple answer...
Reply #8 - Aug 9th, 2016 at 8:09am
 
Hi,

Ok, just tried the suggestion and:

Rotating the top, the "gap" stays on opposite sides (regardless of rotation" and if I sit the top on a glass desk (fully flat) it rocks side to side.

Tried this with a few items and it's the same.

Could it just be the wood flexing? Just seems odd that it's basically identical for any piece I try.

Cheers,

Andy.
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Re: Probably a simple answer...
Reply #9 - Aug 9th, 2016 at 9:01am
 
Andy Mauger wrote on Aug 9th, 2016 at 8:09am:
Could it just be the wood flexing?


When you cut the lid free from the box, the combination of 1. releasing internal stress in the wood and 2. the change in moisture content due to the ambient humidity can and usually does warp wood.
This is why some will cut the lid free and rough out the box and then let sit for a period of time (all depends on your conditions). Once everything has reached equilibrium, you can then final turn will little potential of the wood moving any further.
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Re: Probably a simple answer...
Reply #10 - Aug 9th, 2016 at 2:15pm
 
Andy,

How dry is the wood?
Is it still green?
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Andy Mauger
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Re: Probably a simple answer...
Reply #11 - Aug 10th, 2016 at 3:41am
 
Hi,

Most definitely not green/wet.

The wood in the picture I have had since before I moved to where I am (5 nearly 6 years) and it was only a 3x3x3 cube..

I'm going to try it (another test piece) with some wood that I bought from a local woodturner back in Guernsey 7 years ago and see what happens I think.
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Re: Probably a simple answer...
Reply #12 - Aug 10th, 2016 at 8:04am
 
Andy Mauger wrote on Aug 10th, 2016 at 3:41am:
The wood in the picture I have had since before I moved to where I am (5 nearly 6 years) and it was only a 3x3x3 cube..

Was the wood sealed?
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Andy Mauger
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Re: Probably a simple answer...
Reply #13 - Aug 10th, 2016 at 3:35pm
 
It was, once upon a time. If I remember correctly, I turned a few blanks down to size ready for a project, then moved house and forgot all about it.

When I did the "test piece" the other day though, that specific bit of wood had no sealer on it at all.

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