ENGINES, MOTORS AND TRACTORS 751 



of belting is laced as tightly as possible upon the surface. The size of the 

 pulley has now been materially changed; therefore, the effect upon other 

 machines must be corrected. 



Pulley Fasteners. — Pulleys may be fastened to line shafting either 

 by a key fitting into a key seat both in the pulley and the shafting or 

 by means of a set screw. The set screw arrangement is convenient and 

 is often used where light work is to be done. The set screw may be a 

 source of danger, especially in machines run at a high speed and where 

 they are exposed and likely to catch the clothes of an operator. Also 

 if the set screw once slips and grooves the shafting, it becomes necessary 

 to shift the pulley to a new place. 



BELTS AND BELTING 



About 90 per cent of all the power transmission in the United States 

 is accomplished by means of belts. 



Advantages of Belts. — In the first place, belts are noiseless. Energy 

 may be transmitted by them at a much greater distance than by direct 

 gears. There is less risk of accident than by any other means of trans- 

 mission. They are simple and convenient and are applicable to a great 

 many conditions. In case of breakage they can easily be repaired, and 

 in case machines are moved this means of transmission is the most con- 

 venient. For these reasons belting is especially adapted to farm uses. 



Disadvantages. — Belts are expensive because they wear very easily. 

 They are not always economical of power and unless carefully adjusted 

 and of ample size they are likely to slip. 



Essentials of a Belt. — If a belt has strength, durability, the absence 

 of stretch and pulley grip, it has four very valuable qualities. Other 

 qualities, such as flexibility and resistance to moisture, should also be 

 considered. 



Leather Belting. — The oak-tanned leather is the best material for 

 belting. It has strength and durability, but has a disadvantage in that 

 it comes to the manufacturer in short lengths and if especial care is not 

 taken in cementing the ends together, it goes to pieces very early. It has 

 been found by experience that as high as 25 per cent more power and 

 greater wear may be obtained from a leather belt by running it with the 

 grain or hair side next to the pulley. That is to say, there is a rough and 

 smooth side to leather belts. The smooth side should be run next to the 

 pulley because this side would crack more readily if placed outward, 

 especially in passing over smooth, small pulleys. 



Rubber Belts. — Rubber belting is manufactured by placing several 

 layers of cotton duck and rubber alternately together and vulcanizing 

 the mass into one. The strength of this kind of belt depends entirely 

 upon the quality of the fabric which goes into its make-up. This belting- 

 has the advantage of being waterproof and may be made endless and in 

 any length. Endless belts are not always best in a power house where 



