Sensitivity to Grain Angle
in the
Metriguard
The Metriguard Model 7200 High Capacity Lumber Tester (HCLT) and the CLT Continuous Lumber Tester properly respond to the effects of grain angle (slope-of-grain) in lumber, and therefor the visual graders do not have to consider these effects when they make their final grade determination.
Grain angle produces a profound effect on E and strength because of the strong anisotropic nature of wood. Tensile strength is some 20 to 50 times higher along the grain than in the radial or tangential directions in the softwoods used for structural dimension lumber.
Grain angle is very difficult and sometimes impossible for the visual grader to determine accurately, particularly when the wood is going by at 50-60 lugs/minute. Knots, on the other hand, are relatively easy to see.
A number of years ago a group of well-recognized wood industry experts, including a grading agency check-grader, stood for about an hour examining a dozen pieces of 2x4 lumber. The question of the day was just what was the slope-of-grain in the worst cross section of these pieces. They used a scribe, examined resin streaks and growth rings, probed with pocket knives, and looked at the pieces with a magnifying glass. In the end they agreed only that even under ideal observation conditions grain angle is very difficult to determine visually.
There is a profound grain angle effect on both E and strength. A direct measurement of E using the Metriguard Model 7200 HCLT or the CLT Continuous Lumber Tester provides an excellent estimation of the effects of grain angle, or slope-of-grain.
In fact, if you use the Model 7200 HCLT or a CLT Continuous Lumber Tester, you cannot avoid determining the effects of grain angle while producing MSR, MEL, MGP or E-Rated Lamination grades.
See For Yourself:
One of the wood specimens with this note is cut so the grain of the wood lies
substantially in the direction of the long dimension of the piece. This piece is marked
with a METRIGUARD stamp. The other is cut so the grain angle lies at 30-45 degrees to the
long dimension and is marked with an "X".
The two pieces are matched reasonably well in density because they were cut from the same piece of lumber. The grain angle is very different in the two pieces because of the way they were cut.
Run This Test:
Please Be Advised:
The CLT and HCLT properly respond to the effects of grain angle through the direct measurement of lumber stiffness. Use a Metriguard 7200 HCLT or CLT for machine processing MSR, MEL or E-rated lam grades to ensure that this vital strength reducing characteristic is properly accounted for in your grading. The "X" piece would be rejected.
X-ray testing misses this essential strength-determining characteristic whenever changes in grain angle are not accompanied by changes in density as in the presence of a knot. X-ray measurements do NOT respond to either the grain angle or its effects, so it cannot be relied upon to make an accurate strength estimation when excessive grain angle is present. Both pieces would receive the same grade by the X-ray systems.
For Further Information Contact:
Metriguard Inc
PO Box 399
Pullman WA 99163
PH 509-332-7526
FX 509-332-0485
e-mail sales@metriguard.com
Note - This paper is normally presented with two accompanying wood specimens - one with relatively straight grain and the other with grain at about 30 degrees to the long axis. Both are cut from the same piece of wood, so the density and moisture content are nearly the same. When you submit your request, please include a physical shipping address. One of the annoying limitations of the internet is its inability to actually ship wood.
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