Effects of knife jointing and wear on the planed surface quality of sugar maple wood

Jointing is a common practice required to produce the same cutting circle for all knives mounted in a cutterhead of a peripheral knife planer. Initially the jointed land at the cutting edge has a 0 degree clearance angle, which becomes negative with the workpiece motion relative to the cutterhead and as the cutting, edge wears. Jointed knives could crush a thin layer of the planed board and affect the wood quality and performance. Sugar maple wood gluing properties were evaluated in samples that had been planed using one of four jointed land widths, each tested at four states of wear. With increased jointed land and planing length, the damage to the surface and subsurface of wood increased, but the gluing strength and percent wood failure decreased. The depth of this damaged layer was positively correlated with the magnitude of the normal cutting force. In samples where moisture content had fluctuated, the effects of jointing and wear on gluing were more pronounced. The results suggest that a jointed land of 0.9 mm may be used as maximum allowable width for planing sugar maple wood. Also, the planed surface quality of this wood may be negatively affected using a knife with 45 mum of rake face recession and 60 mum of clearance face recession, which results in a damaged layer 0.20 mm thick.