cracking, splitting

[Max Taylor]

I offer this question as something to start a discussion: Since the pith is the culprit in the cracking and splitting the wood, why not seal just the pith at both ends instead of all over the cut ends? Inquiring minds want to know. Max, disguised as dustpan

 

[hockenbery]

As wood grows is has 3 dimensions

Verticle - the long grain
Radial - across the growth rings cennter of the tree to bark
Tangential - around the growth rings

When wood dries it shrinks in the radial and the tangential directions from 6-12 percent depending on the species. It doesn't shrink at all in the vertical. This is what post and beam construction with green logs relied on.

Moist loss is most rapid through the endgrain.

The pith is problematic because the wood wants to shrink radially whch means from the center of the tree to the bark. this causes the wood to pull from the center toward the bark. This makes cracks in the pith open up.

the wood also wants to shrink around the growth rings. This causes the long splits to open up in a round log.

Cutting through the pith releaves these stresses.

hope this helps
Al

 

[MichaelMouse]

You can get away with it sometimes. Better to use shape to help than just mechanical means though. That way the wood helps control itself. Give a glance at http://www.fpl.fs.fed.us/ and download and read at least the first three chapters of the Wood Handbook.

Woods like yellow birch, elm, aspen (poplars) are almost gimmes, others need a bit of help allowing the outside to shrink and control the interior. Problem is, we all want that 100% guarantee, and that's just not going to happen, even with the friendliest of woods. Staying thin and concave into the heart will improve your chances over coatings alone.

A lot of times there are cracks in the heart area before we even begin to turn. It's very important to detect and avoid including them in a piece, in my opinion. I've never had much luck treating a known split. Detect with a wipe with some mineral spirits. Watch for wicking into the cracks.

 

[TurningDog]

unless the cracking and spitting are going to be dangerous to turn, it don't get concerened about them. Cracks on the outside get a little ca while I rough the inside and anything apprent on the inside gets the same thing. Bigger cracks, voies etc usually get epoxy and an filler. Dangerous looking things just get tossed in the burn barrel, for I have too much wood to worry about turning something dangerous.

 

[Hugh]

If one want to turn a bowl with the pith in it, one can. But the wall thickness needs to be uniform and it is best to seal the pith with CA glue or something like that. Then dry slowly and you can use the pith in you bowl. Some woods work better than others though. Then there are the problem woods that have the crack in the pith when you cut the tree down. I know this is a bit off subject of the original thread - but it is what I thought of when I read the thread. I have done this with vessels as it eliminates all but the pith in the bottom of the vessel. If I remember right - John Jordan used to turn with the pith in the center of some of his vessels and then just drill out the pith and plug it when it was dry.
Hugh