Tag Archives: lumber twist

A Miracle Cure to Prevent Twisted Timber Columns

A Miracle Cure to Prevent Twisted Timber Columns

In 1960 Chubby Checker did a cover of Hank Ballard and the Midnighters 1959 song “The Twist”. Checker’s cover reached Number One on Billboard’s Hot 100 both in 1960 and again in 1962, becoming the only single to reach number one in two different chart runs.

While “The Twist” was a musical hit, twisting in lumber poses concerns, if not panic.

It would be all well and good if trees could be trained to grow so as they only produced straight-grained lumber. Fat chance of this happening.  In fact, straight grained lumber is by far an exception, rather than a rule.

Instead, spiral grain is an expected pattern – where this term describes a helical orientation of tree fibers giving a log a twisted appearance after bark has been removed. This twisted appearance is even more highlighted by surface checks, following grain of fiber, making spiral grain very obvious in some standing dead trees and on utility poles and posts.

This spiral may be in either direction, be fairly constant in any one tree or may change with tree age. In some trees, there may even be a reversal of spiral in successive zones of growth forming an interlocking grain. Lumber twist is a function of the degree of Greater spiral increases chances you will see lumber twist.

Most typically prevailing spiral orientation is in a left direction near a tree’s pith, with angle increasing sharply in first-formed rings in juvenile wood. This gradually decreases to a straight-grain then is followed by a gradual change to a right-angle spiral. Trees with left spiral do tend to twist more with changes in moisture content, than those with both left and right-spiraled grains.

Spiral grain may seriously reduce strength and stiffness of lumber milled from a given tree.  This “slope of grain” in sawn lumber is considered as a defect, and is a resultant of natural spiraling.

For purposes of visual lumber grading rules, slope of grain is wood fiber deviation from a line parallel to edges of a piece. This deviation is expressed as a ratio such as a slope of grain of 1 in 8, 1 in 10, 1 in 12 and 1 in 15. Slope of grain as measured is representative of general fiber slope and local deviations are disregarded. Bigger bottom numbers would express straighter grain. Less lumber twist gives you stronger boards.

Typical No. 2 grade framing lumber allows for a slope of grain of up to 1 in 8 (an inch of slope for every eight inches of board length). This consideration takes into account how this defect accordingly adjusts allowable strength values used in engineering design.

Now – a “miracle cure” for twist!

In this article’s photo, a builder has convinced his client by taking an inch off each corner of his building’s posts (at a 45 degree angle full length) it would somehow keep them from twisting. 

And his client not only believed it to be true – so much so as to help his builder cut off each corner!

Do the Lumber Twist

Let’s start in the forest…

When David Friss of Anchorage worked for NOM ‘s Environmental Research Labs in Boulder, he was once asked why lightning sometimes spirals down the trunk of a tree. While the answer was not proven, we observed the path of least resistance might follow the spiral grain of the wood. He eventually found a tree with a spiral lightning mark and it followed the spiral grain exactly.

“But why should the tree spiral? Larry Gedney, a seismologist at the Geophysical Institute, University of Alaska Fairbanks, speculates: Foliage tends to be thicker on the south side of the tree because of better sunlight. Prevailing winds, in most of the tree-growing northern hemisphere, are from the west. Combine these factors, and the westerly wind pushing on the thicker south side of the tree, year after year, causes an asymmetrical wind loading which slowly twists the tree around in the observed direction.

Lumber wants to do the twist

Professor Hans Nielsen of the Geophysical Institute thinks the matter can be related to the Coriolis effect of the earth’s rotation. In the northern hemisphere, all moving objects are diverted ever so slightly to the right. (This is why hurricanes rotate counterclockwise–air moving toward the storm is diverted to the right and thus imparts a counterclockwise spiral to the storm at the center.) Nielsen thinks that possibly when a tree is rocked by winds, the tip might tend to rotate in a counterclockwise circle when viewed from above. This would lead to a clockwise spiral twist. That sounds like a contradiction until you think about it for a while.

Granted, not all trees exhibit the same lumber twist, but the majority of them do. The phenomenon can be likened to the claim that water will always spiral out of a drain in a counter-clockwise direction in the northern hemisphere.

So…take a log and cut it into nice, new boards. The log goes straight through the saw, but the “helix” of the grain, is not straight. Lumber does have a memory, and if the moisture content of the wood is changed, the cut piece will do the “lumber twist” and try to “become a tree” again!

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