90 FOREST UTILIZATION 



B. ' Durability. 



The durability is said to be for : 

 White pine rived, 20 to 35 years. 

 White pine sawn, 16 to 22 years. 

 White pine (sappy) sawn, 4 to 17 years. 

 Chestnut rived', 20 to 35 years. 

 Cedar sawn, 12 to 18 years. 

 Spruce sawn, 7 to n years. 



C. Specifications. 



The usual size of sawn shingles is: 16 inches or 18 inches long; 

 4 inches wide; 1-16 inch thick at small end; l /2 inch thick at 

 butt end. A bundle of shingles contains 250 pieces, is 20 inches 

 long and has 24 tiers. 



A carload of white pine shingles, weighing 22,000 pounds, contains 

 70,'ooo i6-inch shingles; a large car of red cedar shingles con- 

 tains 170,000 pieces. 



One thousand shingles cover 100 square feet of roof, each show- 

 ing 14.4 square inches to the weather. 



A rule for the number of shingles required for a roof is: ascertain 

 number of square inches in one side of roof; cut off the last 

 figure, and the result is the number of shingles required for 

 both, sides of the roof. In this case, each shmgle shows 20" 

 square inches to the weather. 



Shingles are usually laid to show 4 inches of their length, which 

 arrangement yields, in i6-inch shingles, a quadruple layer of 

 shingles on the roof. The higher the grade of the shingles, the 

 larger is the weather face permissible. 



D. Machinery. 



The machinery used in A shingle plant consists of : 



I. Drag saw, either driven from a countershaft or acting 

 directly from the piston, cutting the logs into shingle 

 lengths. 



II. Bolter, a circular saw cutting the round blocks into bolts, 

 the thickness of which equals the width of the shingle 

 Bolts split with an axe yield a better grade of shingles 

 but cause a large waste of timber. A knot saw may 

 be used after bolting to remove knots, rot, sap etc. 

 III. Shingle machine, constructed in a variety of forms : 



(a) A knife is spanned in a sash frame moving up 



and down and severing a shingle at each stroke 

 from steamed bolts. This system, furnishing 

 "cut shingles," is not much used. 



(b) The shmgle saw machine uses a circular saw 



lacking the loose collar and screwed onto the 

 fast collar. The gauge at the center of the 

 saw may be very heavy while the gauge at the 

 rim is from 15 to 20 only. 

 The shingle blocks are fastened into either a slid- 



