2O8 SCIENCE OF SUCCESSFUL THRESHING 



be allowed the shaft, to prevent danger of heating from 

 the pulley rubbing too hard against the end of the box. 

 A key that is too thin, but otherwise fits properly may be 

 made tight by putting a strip of tin or sheet-iron between 

 it and the bottom of the way in the pulley. 



Fitting Keys. Coat the key with some pasty sub- 

 stance, such as thick paint or heavy grease, and then rub 

 it off so that only a very thin coating remains. Then try 

 the key in place and drive it in lightly. Next withdraw it 

 and the high points at which it bears will be indicated so 

 that they may be filed off. The key should then be re- 

 coated and tried again, this operation being repeated until 

 the key is a good fit its entire length. When the marks 

 indicate that the key fits properly, it may be driven in 

 permanently, but a properly fitted key requires but a few 

 blows with a light hammer in order to remain in. A key 

 should never be left projecting beyond the end of a shaft, 

 as it is liable to catch clothing and injure someone. 



Drawing Taper Keys. A taper key can usually be 

 removed by driving the pulley toward the thin end of the 

 key. Often, however, the pulley cannot be driven a suf- 

 ficient distance to loosen the key because of its coming 

 against a box or another pulley. If the end of the key 

 projects beyond the hub, it may be removed by catching 

 it with a pair of key-pullers or horse-shoe pinchers and 

 prying with them against the hub, at the same time hitting 

 the hub with a hammer so as to drive pulley on Some- 

 times the end of a key may be caught with a claw hammer 



