The S shape

[woodrat]

Here is a question that I have been mulling over for a good while. I would like to know if this is a common phenomena and what others have done to either counter it or work with it. When resawing backs I find that some of the slices that come of well quartered billets decide to cup and other sslices from other billets stay dead straight . This is probably due to the release of tensions in the tree but why does it happen with dead quartered stuff? Recently I sawed some Brazilian Mahogany that had been sawn , dried and stored for more than 8 years and it cupped upon being sliced off a dead quartered billet and yet the PNG rosewood that I sliced at the same time stayed laser straight.
Also I would like to know if in others opinions the timber is still useable. When joined at the edge in a bookmatch for backs it can resemble an S shape which at its rough dimension 3.5 to 4 mm is still quite stiff but becomes much more flexible at its final dim of 2.5mm or 100 thou. I feel that it is still usable but I would like some other points of view.

John

[Bob Connor]

By the time you get that wood down to a little over 2mm it'll sit on your back braces quite nicely and hold it's shape.

It's very usable.

If you want to straighten it out a bit, spritz it with water and clamp it between a couple of thick pieces of MDF.

[Localele]

Partly due to releasing the tension and partly due to moisture gradients in the timber . Even after sitting for 8 years when you open it up it can still be marginally more moist and will equalize after a while.As Bob said dampen them all and glut them for a week with some weight on top and they will probably be fine . That N G Rosewood seems to give up all its moisture evenly and is very stable as dry material. Radial and tangental shrinkage rates of 1% and 2% from memory.Lovely stuff.Cheers.

[J.F. Custom]

Micheal and Bob are right - still very useable.

Wood can often move when it is changed dimensionally, no matter how long it has 'sat there drying' for. As Micheal said the release of tension, the moisture change etc. It's just that it's more noticeable and pronounced in it's effect on thin dimension timber - which can move all over the place day to day if the humidity levels change dramatically. Freaks you out if you're not aware or prepared for it! Larger pieces such as neck blanks can move and twist too if dressed down to size, just usually not as much.

NGR is as Micheal said (is there an echo in here?) a very stable timber. Even in its burl form, Amboyna, which is one of the busiest burls, it tends to stay perfectly flat when re-sawn dry.

Cheers,

Jeremy.

[woodrat]

Thank you , gents, for your thoughts. I was of the opinion that it was still very usable so it is good to have confirmation of this. After all we ask it not to stay flat but to bend itself to our will when we strap it down to a curved brace.

Regards to all

John

[Tom West]

John: Don't know if this wood was kilned or not but faulty kilning can cause similar problems. Think you will be fine after working to thickness and bracing. Cheers,Tom.