The pith.....

[sdb777]

I know what it is...

I was just wanting to know why I can't leave it in when turning? Not like I'm not going to finish the surface of the wood, thereby sealing it.....


I'm asking cause I've got about 30-ish cedar blanks I cut up that have the pith still in them. I don't want to send them out to people and get one of those 'bad names', but I can't bring myself to just throw them out.



Scott (what says the forum) B

[admin]

It can cause splitting if left on. Mr. Cody or Mr. Tim can elaborate further. I just know when I quit leaving pith on, I stopped losing bowls and spindles to splitting. (It's most prevalent with spindles, if ya just take a slog, put it in the lathe and turn it with the pith in the center, it'll split pretty much every time. If you split the piece into quarters, it normally doesn't. It's been months since I lost a spindle to splitting. )

[Doug B]

With dry wood it is probably not a problem...any splitting caused by the pith is going to have already happened if it was going to. The pith has virtually no water content, so the difference between it and green wood is significant.

For green wood that you want to prevent from splitting, you really do need to cut the pith out.

[Mark]

Scott,

Good explanation already started, but I'll add my observation. It depends on the species as well. Oak is notorious for warping anyways, and if the pith is left in, it's gauranteed to split. On the other hand, I've left the pith in on Juniper turnings, without problem.

Your cedar may be closer to Juniper than to oak, so I'd suggest taking a couple of those blanks, and laying them in a sunny windowsill for a week or so. If they're going to split, it won't take long. The mechanical forces inside the wood created from differential shrinkage while drying, may overpower the strength of the fibrous structure of the wood, causing it to fail. But then again, it might not.

Thanks,
Mark

[oakridgeboy]

It's a well-known fact that you should always put the pith in a near-by pot--assuming of course that one has a pot to pith in ;D ;D ;D
Mike

[Doug B]

That was a pith poor reply Mike ;D

[imahic]

Hope he don't get pithed off with thoth thmart ath amtherth.

[Doug B]

;D ;D ;D

[Ruffnek]

Yes, the pith is prone to cracking...in fact, it almost always will.

However, I've turned many bowls and vessels with the pith left in. If it's turned thin and the pith is then sealed with CA glue, there will be no cracking beyond what has already occurred in the pith before turning. It's really no different than a knot which is nothing more than the remains of a limb which also has a pith.

The pith can be cut out and a stable plug of the same or contrasting wood glued in place. I've done that a lot, too.

Now, even though I do it myself, I don't think I would sell bowl blanks with the pith left in them, unless it was stated up front.

[TDHofstetter]

Gotta' love them pithy comments up there ^^^...

The biggest factor is wood species. Some woods that don't move much are perfectly happy with the pith left in place, while other woods really give ya fits if you get anywhere near it - ring shakes, radial shakes. Sometimes inner radial shakes, sometimes outer radial shakes, depending on how that species of wood moves as it dries.

Most species of wood have two distinct movement characteristics - radial movement and circumferential (sometimes imporperly called "tangential") movement. In most species, those two directions of shrinkage occur at different rates. If the two shrinkage rates are very closely matched to each other, or if both rates are very low (certain mahoganies, for example), there's no problem leaving the pith in place.

[triplefreak]

I think this post is pithyful. Bwhahahahaha. ;D