A study is described, carried out on specially prepared specimens, that specifically examines the effect of slope of grain on the bending strength of scaffold boards. Each specimen was visually graded and both the modulus of rupture and modulus of elasticity in bending determined. From the effect of slope of grain on the reduction of bending strength revised visual grading rules have been suggested that include a slope of grain limit of 1 in 12. It has also been demonstrated that machine grading is as effective at determining the adverse effect of slope of grain on board strength as it is for other defects such as high rate of growth and knots.
Pope, D., Marcroft, J. P., & Whale, L. R. J. (2005). The effect of global slope of grain on the bending strength of scaffold boards. European Journal of Wood and Wood Products, 63(5), 321-326. https://doi.org/10.1007/s00107-005-0010-y