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How do I tell if my wood is case hardened. I was reading baout it last night. This rough cut white oak I have I moticed is cracking on the ends in a few places. One small board has craks on one of the faces too.
Is it possible to still use the wood or will it continue to split and deform even after cutting and planing?
You cut two slits into the edge, so the cross section looks like the tines of a 3-prong fork.
If the tines curl inward, it's case-hardened.
I got that from the Bruce Hoadly book - Understanding Wood. He says this is the technique Kiln operators use.
Set your font to be mono-spaced, and not proportional. A font like The Courier or Typewriter font should work. Here is the edge view of a slice of wood.
+----+ +-----+ +-----+ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +-----+ +-----+ | | | | | +----------------------------+I'm not sure how much of a cut-off from the end you need. The picture in the book looked like it was about 1/4 inch thick. But if the slice was from the end of a board, I'm not sure if that would work the same as a slice inches in from the end.
You can see the three points, or "tines" above. If the left and right curl towards each other, it's case-hardened. The book doesn't say how long it takes to curl. I think Brian's message about the saw gripping the board suggest that it doesn't take long.
The problem with case hardening - according to Hoadly, is that the outside is stable, but the inside is under stress, and honeycomb cracks can form internally. This is the worst type of failure in wood, as the wood loses strength internally.
In order to conceal my ignorance, I've been waiting for someone else to ask, but I guess it's going to be up to me. To me, "case hardening" has always meant a process for adding carbon to the surface of steel. I have never heard the term used with wood, and I am baffled. What do it mean?
new to forks, too??
Mac
Hardening of the outside of wood, same as hardening of the outside of metal. We turners meet it commonly when we sand with excessive pressure. The surface hardens, leaving us with a slick-looking hardened surface which highlights the old scratches. We dampen the surface to break the hardening and sand with less heat generation to compensate.
Also happens in kiln-drying, where the normal process injects steam late to reverse the hardening.
Bruce Hoadley's book is interesting (I corrected my misspelling of his name). He says the wood drying process had three phases. As part of the process, wood drops to a point where water no longer passes through it easily. If this is done too fast, the outer part (shell) reaches this stage while the inner part (core) is still high in moisture content. So the inner core is swollen/larger that when it stabilizes. As it dries - checks form throughout the wood as the core shrinks yet the shell remains the same size. Any place you cut it, there will be small checks.
To duplicate it, take greeen wood, coat the ends, and pop it in a 212 degree oven. In a day or two, you will have a case-hardened board.
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