The Mystery of the Pith

[Jon Lanier]

I new it happened, but didn't know why it happened. Had to know the answer to: "Why does the pith cause cracking." Well here is what I found out.

The wood doesn't shrink evenly! It may shrink by 4% in the radial dimension, but 6% in the tangential dimension. If both shrinkage rates were the same, then you could dry a round without it distorting.

But back in the real world, the radius of the round has shrunk 4% and the circumference has decreased 6%. The missing 2% is the crack. If the pith isn't included in the blank, the effect is much reduced and the piece usually just pulls itself slightly out of square.

I'm sure this has been explained somewhere on this board, but I couldn't find it and thought maybe some other newbies (wood) be interested in the science behind the mystery of the 'pith'.

[John Hart]

Ya got it all wrong Jon. I know that all that scientific mumbo jumbo is easy to get sucked into....but the fact is....the pith is evil. Plain and simple. It looks for the nicest figure and sends a little lightning bolt through the wood, straight at the figure and destroys it. Sometimes it will watch you....following your eyes as you gaze at the possibilities...then when you're sleeping, it will chuckle softly as it sends more lightning bolts into the wood where you were looking. I hope I've cleared this up.;)

[Justin Bukoski]

John, you just described my ex-wife to the tee. She must have been made out of pith...

[Bernie Weishapl]

ROFLOL John that is good. I never knew that.:D:cool:;):rolleyes:

[Jason Christenson]

I hate the Drake! I mean the pith.

Jason

[Tom Sherman]

Jon's explanation would seem to appeal to the engineer types with its data, but I too like John's better seems to be more accurate.

[Jeffrey Fusaro]

Ya got it all wrong Jon. I know that all that scientific mumbo jumbo is easy to get sucked into....but the fact is....the pith is evil. Plain and simple. It looks for the nicest figure and sends a little lightning bolt through the wood, straight at the figure and destroys it. Sometimes it will watch you....following your eyes as you gaze at the possibilities...then when you're sleeping, it will chuckle softly as it sends more lightning bolts into the wood where you were looking. I hope I've cleared this up.;)

john--

your unique ability to make the complex 'simple' is precisely why you have been sorely missed over the past several months.

welcome back.

[robert hainstock]

Huh!:confused:

[William Bachtel]

The real reason the pith cracks is it loses water.

[Ed Scolforo]

Pith cracks because you can't make another word out of it.. :confused:

[joe greiner]

John's explanation is probably as good as any, as far as dealing with it is concerned. But I think the technical reason it causes trouble, is that it's harder than the sapwood and it has lower moisture content. As the sapwood dries, it shrinks mostly circumferentially; it tries to reduce its radius to accommodate the circumferential shrinkage, but has nowhere to go because the harder pith is in the way. The sapwood's only recourse is to crack; most wood has very little tensile strength across the grain, in contrast to other directions. I hope this doesn't spoil the fun.

Joe

[Sean Troy]

John, you just described my ex-wife to the tee. She must have been made out of pith...

I see you were married to my EX also.

[Roy Hatch]

And all the time I thought that pith was thomething you couldn't when you had prothtrate problemth. :)

[RL Johnson]

This discussion is begining to pith me off.:D

[John Hart]

You're too thensitive.