22 BULLETIN 118, U. S. DEPAETMENT OF AGBIGULTURE. 



continuous; it is not us capuble of control us is steam, and in most 

 cases it gives low speed and low capacity. Decriptions of various 

 types of water wheels will be found in the Appendix. 



BELTING. 



Belts transmit power from the engine to the saw. The heavier the 

 belt the more power it transmits. Belt tighteners are required when 

 a belt itself is not heavy or long enough to cause sufficient sag. The 

 sag should alwa3^s be on top, in order to increase the arc of contact 

 Avith the pulley. Belts are made either of leather, rubber, or 

 fabric. Leather belts are sold either single or double. The trans- 

 mitting power of a single belt is only TO per cent of that of a double 

 belt. Rubber belts stand moisture better than leather and are cut 

 from -J to ^ inch shorter per foot than the circuit on which they run. 

 The}^ are run with the seam side out, while leather belts are run with 

 the grain side in. Rubber belting is sold as 2, 4, 6, and 8 ply, the 

 4 pl}^ being equal to single leather belting, the 6 ply to light double 

 leather belting, and the 8 ]Aj to heavy double leather belting. Small 

 mills are usually equipped with either fabric or rubber belting. 



When ordering belting of any kind it is necessary tO' specify 

 (1) diameter of driving pulley, (2) its revolutions per minute, 

 (3) diameter of driven pulley, (4) distance of pulley centers, 

 (5) horsepower to be transmitted, and (6) width of pulley face. 



Leather belting is spiked or joined either by studs or by belt 

 cement. Next best to the cemented joint in a leather belt is that 

 made with a rawhide or other lace. But this joint in a leather or any 

 kind of belt must be made properly. Large lacing holes and a big 

 bunch of lace may be almost as harmful and cause as much " jump " 

 in the belt as a double row of studs. Where leather belting is ex- 

 posed to moisture and waterproof cement is not accessible, lacing 

 may be resorted to; but, as a general rule, all leather belts should be 

 cemented. 



In lacing a fabric belt never use a hollow punch, because it cuts 

 the stitches and weakens the belt. Use a pointed awl. Cut the ends 

 of the belt perfectly true with a try-square and punch or bore two 

 rows of holes in each end. The holes in the second row should be 

 punched directly back of the holes in the front row. The holes in both 

 ends of the belt should also be directly opposite. No hole should be 

 less than one-half inch from either edge or end of the belt. The holes 

 should be spaced three-fourths inch from center to center. "\¥lien 

 an odd number of holes are to be laced, begin with the center hole ; 

 and when an even number, start with either of the two center holes. 

 The straight stitch and hinge are the two forms of lacing in most 

 general use. Other methods of splicing fabric and rubber belting 



