I use logs and site-milled timbers in my work, and as I search for which logs to use where, I study the logs for twist. A log or timber with grain that twists more than 1 in. for each 10 in. of length is used only in certain areas, such as the first couple of courses in a log house where the weight of the upper logs will stop the bottom ones from twisting. In critical areas such as roof systems, spiral grain must be less than 1 in. in 20 in.
To track the twist in a log's grain pattern, I use the grain scribe illustrated here. This simple tool starts out as a 4-in. strap hinge. I bend one end of the hinge so that it's perpendicular to the hinge knuckles. Then I run a bolt through the bent end and sharpen the bolt to a fine point. The other end of the strap hinge ends up inside a wooden handle.
To use the grain scribe, I snap a chalkline down the center of the log and place the scribe's point on the line at one end of the log. As I pull the scribe down the log, its point follows the grain. The hinge allows the point to follow the grain around knots and other imperfections. Measure down the log in multiples of 10 in., and then measure the distance from the chalkline to the point of the grain scribe. The distance from the line to the scribe point over the distance traveled is the ratio, or grain slope, of the log.
Mike Hoffman, 108 Mile Ranch, BC, ca
From Fine Homebuilding 120, pp. 32
January 1, 1999