Force and Work to Shear Green Southern Pine Logs At Slow Speed

Logs of three diameter classes and two specific gravity classes were sheared with a 3/8-inch-thick knife travelling at 2 in./min. Shearing force and work averaged greatest for dense 13.6-inch logs cut with a knife having a 45? sharpness angle (73,517 lbs.; 49,838 ft.-110.e). Force and work averaged least for 5.1-inch bolts of low density when cut with a knife having 22-1/2? sharpness angle (9,975 lbs.; 2,885 ft.-lbs.). Values for 9.7-inch bolts were intermediate. At a cutting velocity of 2 in./min. and with cutter thickness constant at 3/8-inch, shearing force (Fr, lbs.) of green southern pine at 60 to 80?F. p can be expressed in terms of bolt diameter inside bark (in.),. sharpness angle (beta, deg.), and wood specific gravity (ovendry weight and green volume). For green southern pine logs sheared with bark in place: Fp = 76,268. ,173 (dia.) 104,4.85 (sp. gr.) +373 (sharpness angle) (1) Within the range of the factors tested, equation: (1) accounted for 81 percent of the variation. Standard error of the estimate was 9,680 lbs. Work to shear (ft.-lbs.) is expressed: Work = – 71,538 4,048 (dia.) 102,589 (sp.gr.) 171 (sharpness angle) (2) Within the range of the study, equation (2) accounted for 93 percent of the variation. Standard error of the estimate was 4,500 ft.-lbs. When sheared logs were viewed in radial section, each annual ring showed a check at the earlywood-latewood boundary. Checks were least severe in small logs sheared with the 22-1/2? knife; they were most severe in large logs of low. density sheared with. the 45? knife. Each sheared log generally also had one to several rather lengthy checks that formed just prior to emergence of the knife. Average check depth (in.) of green southern pine sheared at 60 to 80?F. can be expressed in terms of bolt diameter inside bark. (in.) and sharpness angle (beta, deg.). Wood specific gravity proved to be not significant. Average check depth = 0.411 0.0147 (dia.) 0.0172 (sharpness angle) (3). Within the range of factors tested, equation (3) accounted for 55 percent of the variation with standard error of the estimate of 0.19 inch. In an equation for maximum check depth in inches (ignoring the large splits occurring near knife emergence), only sharpness angle was significant: Maximum check depth 0.0944 0.0588 (sharpness angle) (4) Equation (4) accounted for 39 Percent of the variation with standard error of the estimate of 0.85 inch.

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