The Working Line is a line on the side of the 

 rafter parallel to the top and lower faces, and passing 

 through the heel of the lower cut. See Cut No. B.M.-8. 

 All length measurements for rafters must bo made on this 

 line. To try to work without this line will land you in 

 certain trouble. 



To get the length and cuts of e common rafter - 



(1) Decide upon the pitch to be given the roof. In 

 the following examples this is assumed to be 1/3. If you 

 are not familiar with the computation of pitch from the 

 carpenter's square, refer to Cut No. B.M.-7 and you will 

 find that 12 inches on the tongue and 8 inches on the 

 blade of the square will give you this pitch. 



(8) You must know the width of the building. In 

 the following example this figure is assumed to be 24 feet. 



(3) Lay off the projection and mark a square line 

 across the side of the rafter at the upper end of the pro- 

 jection. As a general rule for rough building the pro- 

 jections will be GS follows: 



-Roof -of 1/4 pitch 18" 



* u 1/3 " 15" 

 ti Ti 1/2 u 12 it 



* s i 5/e H 9 



I 



(4) Mark off the bottom cut. In doing this remember 

 that the rafter should have a seat as wide, or nearly as 

 wide as the plate, or sey,' 4 inches. Now place the square 

 on the rafter with the 12 inch and 8 inch marks as shown in 

 Cut No. B.I.1.-7 for 1/3 pitch, on the lower edge of the rafter 

 and the 16 inch mark on the cross line at the upper end of 

 the projection. This will give the line of the bottom cut 

 as in Cut No. B.M.-8, Fig. 8. 



(5) Lay off the work line through the point "A" at the 

 heeJL of the bottom cut. See Pig. 7, Cut No. B.M.-8. 



(6) To find the length of the rafter place the square 

 on the rafter in the position shown by Fig. 7, Cut No. B.M.-8 

 and mark the point where it crosses the work line. Slide 



B.M. (S3) 



