Cutting "shake" out of logs

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What is shake, why does it occur, and how can it be removed? April 29, 2003

A guy who wants to buy my redwood timber has asked me to cut the shake out of the boards so that we'll get the high value lumber. What is shake? How do you trim it out of the wood/log?

Forum Responses
(Sawing and Drying Forum)
When I think of shake I think of "ring shake" where wood has separated between the growth rings in a vertical direction and with some amount of width going around the tree. If it's small enough you can put it horizontally in your cant and isolate the bad spot in one or two boards, hopefully.

Virtually 100% of the shake (separation in wood that runs parallel to the rings) is due to the weakening of the wood due to bacterial action. In addition to the separation, there is also a higher MC, more collapse likelihood, smell, poor color, and generally lower strength.

Lumber is sawn from a log so that the shake is confined entirely within one quadrant of the log, if possible. In this way, only 1/4 of the lumber will have shake (maximum). Because shake moves slowly up the tree only a few inches per year, shake can be eliminated from lumber by trimming the piece shorter.

Gene Wengert, forum technical advisor

From contributor R:
Picture it like this... a straw inside a bigger straw. If you stood it upright sometimes it just falls out the bottom, leaving a perfect hollow tube.

I run into this death trap just about every day. A log with any taper being cut on a circular is real scary. You can only cut parallel to the shake twice, then the fun begins. When cutting across the shake, the loose wood inside the cut (ends up shaped like a wedge) likes to jam between the saw and the board or between the saw and the offbearer, or sometimes it will come shooting out of the cut like a rocket. The logs with shake that I saw are usually full length and full circumference. I've had numerous centers fall out of the log that look like a perfect fence post. Shake just plain sucks, so be careful.

From contributor J:
I have had ash and E. hemlock boards literally fall apart out of logs that have shake. It usually runs full length of the log and you end up with very few usable boards.

Shake moves about 1 to 1-1/2" up the tree every year, so it takes well over 75 years before the shake is 6 feet up the tree. That is, shake is confined to the lower part of the butt log, unless you have a very old tree (or if the logs have been ponded for a long time in stagnant water).

Shake bacteria also enter the tree through the root system, which means that the shake is usually confined to a small zone which will occupy no more than 1/4 of the circumference. (Not true for E. hemlock, which often can have shake totally around the stem. With E. hemlock, the concept of a straw inside a straw idea is okay, but typically not in other species.)

Gene Wengert, forum technical advisor

From contributor R:
Gene, I see a lot of red oak with shake 3/4 of the circumference. A lot of ash that is 1/2 to 100% around the circumference. And quite a bit of soft maple. When I said a lot of logs, I meant 500'-700' of logs per 10,000' sawed. And hemlock is the worst.

But the way our mill works, is... We have 8 logging crews cutting, 3 log truck drivers hauling 6-7days a week. When the logs get here in the yard, we have 4 different veneer buyers pick through the logs, and then 3 other buyers take export and sawlogs. I get left with the crap logs that didn't sell. So I guess my statistics are a little skewed, with all the logs I cut being slightly better than firewood. But on occasion I do get a few veneer rejects (then I feel like a kid at Christmas).

Note that I said "usually confined..." Sometimes it does indeed go further, but not too often.

Gene Wengert, forum technical advisor

I'm a little lost here... I thought shake or ring separation was caused by wind damage. I always noticed that it happened in specific areas, and was worse on certain species.

The bacterial action weakens the wood. Then when there is a wind storm, the tree fails. The defect is called shake or wind shake. The bacterial damage is typically much wider spread than just the shake area.

I should have added that the bacteria that enter through the roots will be more often found in rocky soil and wet soil. They prefer older trees and some species more than others. They prefer sites where there has been soil disturbance, such as previous logging or cattle grazing. Hence, you will find bacteria and shake in some sites and not others.

Gene Wengert, forum technical advisor

Can all trees become infested?

From contributor J:
I have a 16' ash log that has shake from one end to the other. It was harvested from woods on shallow ground with only a foot of soil to the bed rock.

I have also had a hard maple log with shake. The wood had that characteristic smell of infection. Total loss on that log as the shake went through the whole thing and every board fell apart.

Any species is a candidate, but the soil and weather must be proper, along with root damage.

Contributor J, the comments I made are for the typical. There will always be one case of untypical. Of course, if the wood has been in a tornado, it might develop shake without a bacterial presence. It would be nearly impossible for shake to go 16 feet in a log (require over 150 years), so you must have shake caused by something else. As the bacteria involved is anaerobic, it would not be found entering a wound in the tree above the ground.

Gene Wengert, forum technical advisor

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
Here in England shake is a problem in some of the oak that we see. As well as ring shake we get occasional star shake, which is like far-reaching drying cracks that radiate from the pith. The story goes that European Oak (Q Robur) that grows on sandy soils is far more susceptible to shake than those grown on clay soils, where they grow a bit more slowly and without the summer dry spells found on lighter soils.