112 



ENGINEERING ON THE FARM 



to dimensions and grade, are taken from the table by labor- 

 ers, placed on hand carts, and piled for curing in a place 

 convenient for shipment. The lumber as it comes out of 

 the sawmill is usually wet, green, rough, and cut to ordinary 

 stock sizes only. 



Defects. The defects that occur in lumber may be inci- 

 dental to the growth of the tree or due to improper handling 

 and sawing. Sapwood is soft, and usually it will shrink, 

 warp, and crack in curing. The pith or center wood may be 

 rotten, soft, and cracked. Pitch pockets are irregular open- 

 ings filled with pitch which may occur anywhere and weaken 

 the piece. Ringshake is a lack of bond between the annular 

 rings which permits them to separate easily (Fig. 113). 

 Heartshake is a series of radial cracks (Fig. 114). Knots 

 are formed by limbs which start their growth near the 

 center and may, have been alive at the time the tree was 



cut or may have been dead and healed 

 over by sapwood and bark. The saw 

 may have cut across these knots, leaving 

 an irregular defect circular in shape, or 

 lengthwise, leaving a pyramidal-shaped 

 defect called spike knot (Fig. 115). Well- 

 formed knots that have been dead for 

 some time become loose and fall out on 

 curing. Green knots are usually tight 

 and remain in place, but frequently exude 

 pitch or sap. Knots greatly decrease 

 the tensile and bending strength of a 

 timber, but tight knots are not a serious 

 defect in compression. The defects that 

 occur in some woods which give it the 

 name of curly or bird's-eye are due to 

 buds that form each year in the sapwood 

 and never develop. These are not truly defects, as they 

 do not injure the timber and usually give it an increased 

 value for ornamental purposes. Worm holes and dry rot 



Fig. 113. Ring or 

 ivindshake 



Fig. 114. Heartshake 



