Delamination of roughed bowl blank

Re:  Delamination of roughed bowl blank

John Jordan

Sounds like ring shake, which is common in cherry. Maybe had nothing to do with the drying. I would recommend he not turn it at least until he has more experience.

John

Re:  Delamination of roughed bowl blank

Mike Stafford

John, I considered ring shake but this is only one layer and only on one side of the bowl. It just doesn't look like any ring shake I have seen.

I don't approve of his drying method but he is convinced it does not harm the wood. Personally I think he is "case hardening" the wood.

I found this when I was looking for an answer for the condition his wood was exhibiting...

"Case hardening describes lumber or timber that has been dried too rapidly. Wood initially dries from the shell (surface), shrinking the shell and putting the core under compression. When this shell is at a low moisture content it will 'set' and resist shrinkage. The core of the wood is still at a higher moisture content. This core will then begin to dry and shrink. However, any shrinkage is resisted by the already 'set' shell. This leads to reversed stresses; compression stresses on the shell and tension stresses in the core. This results in unrelieved stress called case hardening. Case-hardened [wood] may warp considerably and dangerously when the stress is released by sawing."

Re:  Delamination of roughed bowl blank

john lucas

Ditto what John Said. I have seen it in Bradford Pear and some Cherry that I got. You can't see it from the outside but once you start turning it appears. Very dangerous. I had 4 bradford pear go down in a storm and every piece I cut from the trunk portion of the tree had it. When I was lucky I could see it from outside but other times didn't find it until I was half way through the bowl.

Wind shakes

jorge

Wind shakes is another name for it. In cherry I've seen it many times sometimes a whole ring about 2 inches around the pith

separates from shaking in high winds. Seen this also in ash and red oak from the wood around here

Also happens in lightning strike trees

Dick Coers

A lightning strike can cause the same issue. I think it’s a problem with the lignin being changed from the heat.

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

Im with John on this,

Keith Newton

If it followed the annual ring, that was already there. If it was from drying unevenly, those are perpendicular to the rings, or radially from the heart.

As for lightning, yes it can cause something similar, but there will always be a little crease where the scar tissue meets in the middle as it comes in from both sides capturing a little bit of bark.

Depending on the severity, some may heal over within the same year, but some may be 5-6” wide and take several years. In those you can see where the annual ring curves in and terminates against the year before, maybe several times befor it meets the new scar tissue from the other side.

Re:  Delamination of roughed bowl blank

Ric Taylor

I used to microwave wood but it has been a long time since I tried it. I only did small pieces, never a roughed bowl.

When something is microwaved, it is cooked/heated from the inside out, the center is what gets hot. What I did was a process that was mentioned on many forums at the time. I used the defrost cycle and turned it on for 20 seconds, then let it cool for at least 15 minutes, usually more. This required many cycles, and with other things going on it would usually take a couple of days. I had success but in the end I decided that it was too much hassle and I quit doing it.

My WAG is that your friend may have used a power setting that was too high, and didn't allow enough time between cycles for proper cooling.

Re:  Delamination of roughed bowl blank

Mike Stafford

He microwaves on high for 20 seconds. He says it is too hot to handle at the end of the cycle. I am still convinced his drying process damaged this wood.

I have seen wind shake, wood damaged by felling and a number of structural problems caused by the wind. We live in a hurricane zone so wind damaged trees is a common problem.

This looks different as it only affects one set of annular rings.

No answer....enough time wasted on this as I don't believe he will change. He is always in a hurry to turn....

Even leave  hoe out in the rain?

Bill Tindall, E.Tn.

Or a shovel, or any other wood handled tool? A few wet dry cycles and the wood delaminates at the growth rings. I suspect the dry/wet cycles accomplished the same thing. Some time during this course of events the outside was bone dry and the middle still wet. The outside was trying its best to shrink but the inside would not let it. The stress simply fractured the outside along the weak rays of the wood. Happens all too often drying oak (weak rays that easily fracture under stress) if the schedule is too aggressive. 60 microwave cycles was certainly aggressive.

Personally, I have seen a lot of cherry sawed and never seen shake in cherry. The heartwood of cherry is usually fractured but this is not the same phenomena as the ring shake common in hickory or hemolck, for example.

I don' t know anything about turning bowls. But end grain looses water around 10X faster than flat grain. I would think a bowl would dry sufficient in days with good circulation. The challenge would be keeping these things from drying too fast.

Re:  Delamination of roughed bowl blank

Ric Taylor

There it is, microwaving on high power is part of the problem. He should be using the defrost cycle or low power. And no mention of how long he waited for cooling between cycles.

Example

Bill Tindall, E.Tn.

Let me preface by saying I know nothing about drying bowls. But I have dried a lot of lumber for our former business. Round stuff dries different from flat stuff, and bowls may fall in the category of round stuff. Shown is a shovel handle that got wet too many times, and dried too fast in the sun. Note is it not split radially, like a board would split if dried too fast. Rather, it has split along the growth ring boundaries, perhaps like the bowl in question. Wet handles always split this way, not radially.

BTW, "wind shake" is more likely to be caused by infection or other factor that affects the adhesion between growth rings. See Richard Jones, "Cut and Dried" page 215, for example.