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[QUOTE=Alan Carruth]The splittyness is a real issue, and about all you can do is realize that it is and take precautions. Mostly, avoid shock loads, such as sawing a thin top with a skip-tooth blade.
Ken Parker used redwood as a cor material in the early 'Fly' guitars. He said it tended to have a real split personality: some pieces were fine, and others were unstable, splitty and all in all hard to work with. He switched to spruce, iirc, and never had any more problems of the sort. I've noticed the same thing. When redwod is good, it's very good, but when it's bad, it's terrible.
One issue: trees put on their new wood in tension trelative to the layers underneath. This, of course, puts a compression load on the inside of the tree. On big trees the compression and the weight of the tree can combine to exceed the compressive strength of the wod, and it will microfracture. You can't see this, but the wood will tend to fail catastrophically in bending. I've seen other types of flaws in redwood that could be related to this as well. [/QUOTE]
I had two redwood tops split unexpectedly. I had resawn them from a nice qs plank. They were adjacent cuts, too. So, I went back and looked at the tops that were adjacent to these two and noticed a very fine light colored line right where the splits occurred. Not a crack. The only reason why I noticed it as being slightly different at all was because I was able to stack the tops together and examine the end grain, comparing the split pieces with the ones still intact.
So I tested the next top set in the stack, flexing it moderately, and bang. It busted into two pieces, right on that line.
Something I discovered when I resawed my first sets of redwood was the wood can develop internal cracks that are not necessarily visible until you start resawing. I was using a friend's bandsaw to do the resawing at the time (a big honking 21" Felder), and showed him the cracks that became uncovered after resawing a few pieces. He called them -- I forget the term he used now -- something like "wind splits." He explained that, when the tree was young and flexible, it had probably been subjected to high winds, causing it to bend to the point of splitting internally.
So, I got to thinking that, if this is true, then possibly the light colored lines I observed were close to where splits had developed further into the tree. I would check through my stash to see if there is any veracity to this, since I've kept some of the tops that have the cracks in them, and see if the light lines might coincide with the splits. But I can't right now. I'm in Connecticut as I type this, about 1700 miles from home. (I'm here for the 2nd Annual International 10-string Guitar Festival, held in Faifield, CT this year. I'll post pics later. Just got in about an hour ago.)
Also, I've also had splintering issues when trimming tops to approximate shape. For me, a jig saw I used to use for this was the worst culprit. To eliminate this from happening anymore, now I always cut the tops to shape before I thickness them. Even when using a 4tpi bandsaw blade (not a skip tooth, though), it isn't a problem anymore.
Best,
Michael
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