742 JOURNAL 01- FORESTRY 



up of wood fibers arranged in annual layers it is evident that there are 

 two principal ways in which cross grain may occur. 



(a) The annual layers may not be parallel to the' axis of the piece. 

 This results in diagonal grain. Diagonal grain is most readily deter- 

 mined by inspection on quarter-sawed surfaces, that is, surfaces which 

 are radial to the direction of the annual growth rings. 



(b) The wood fibers instead of being vertical in the tree may wind 

 around it in a cork-screw curve or spiral. This is natural spiral grain. 

 If a piece from a tree which is free from natural spiral grain is cut in 

 such a manner that the wood fibers as observed on a flat-sawed face are 

 not parallel to the axis of the piece a phenomenon somewhat similar 

 to natural spiral grain is produced and the piece may be said to be 

 artificially spiral-grained. 



In order to correlate cross grain in timber' with its strength prop- 

 erties, it is necessary to have some measure of the cross grain. This 

 is furnished by the angle between the direction of the fibers and the 

 edge of the piece. This angle is usually expressed as a slope, for in- 

 stance 1 in 15, or 1 to 15, means that in a distance of 15 inches the 

 grain deviates 1 inch from the edge of the piece. 



Because of the dif^culty of getting comparable material with natural 

 spiral grain of various slopes, tests were made on sticks containing 

 artificial spiral grain. The standard size of stick for these tests was 

 2 by 2 by 48 inches. Sticks from each plank were made straight- 

 grained and with various slopes of spiral or diagonal grain. This 

 provided specimens which were inherently similar except for the dif- 

 ferent slopes of grain. Approximately one-half of the sticks of each 

 slope of grain were tested in static bending and the remainder in im- 

 pact bending. Following the bending tests a piece for test in com- 

 pression parallel to grain was cut from each stick of ash whenever 

 sufficient uninjured material remained. Tests were made on about 

 1,800 sticks of Sitka spruce. 900 of Douglas fir, and about 1,800 of 

 commercial white ash.^ 



Sticks were cut with as near as possible predetermined slopes of 

 grain but in order to avoid mistakes in slope classification all sticks 

 were examined after test and the slopes of both diagonal and spiral 

 grain at the point of failure determined. When a piece had both 



'This material is termed commercial white ash because although the exact 

 species were not known it was all from species classified in the market as white 

 ash. 



