Turning

Subject:
Re: Delamination of roughed bowl blank

John K Jordan
Mike,

It sure would be nice to see and touch it. Is the delaminated part still tightly bound everywhere except for the very edges or will it come loose if you pull on it?

The rapid drying defects I'm familiar with don't separate along the rings but small areas collapse inside a thick piece, for example a type of severe internal checking called honeycombing. I've seen it in kiln-dried Oak and Maple. From what I've read about case hardening it causes severe stresses in the dried wood (under tension on the outside and under compression inside) that can, for example, pinch a saw blade when cutting, but not cause separation or internal checking.

Without seeing it, when I read your description my first thought was like the other Johns, ring shake. I've seen it in walnut, chinese chestnut, cherry, and even once in mesquite. The delamination can be severe - all the way around the ring in multiple layers, just a single tiny portion, or anything in between. It is not unusual for it to be on one side of the log and not the other.

Ring shake is in the tree when cut but may be tight and not evident until dry.

In some cases I've had chunks of wood fall apart while chainsawing. Others don't show up until the wood is cut into turning blanks and have dried some. It is not unusual for the wood appear to be OK at first with the rings tight then separate during drying. Just recently I sliced a piece off the end grain of mostly dry blank - it had a check from the side that went about an inch radially following a ray before it turned and followed a ring maybe 20 degrees or so. I threw the whole blank away.

One question about the microwaving - is this the first time he's done this and were past dryings successful? How long was a typical cycle? I've only dried small pieces with a microwave, 1"x1" spindle blanks and it did take a lot of cycles. I'd run the oven for just 20 seconds or so until the outside felt warm, not hot. Let cool then weigh. Repeat. Seems like it only took 15-20 cycles for that size of wood.

Does he still have scraps from cutting out the bowl blank. I'd want to get those and cut and examine thin transverse slices by bending. I test every blank this way that I process from green wood.

JKJ

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