204 



Tables 166-168 



TABLE 166. — Friction 



The required force F necessary to just move an object along a horizontal plane =/W where TV is the normal pressure 

 on the plane and / the " coefficient of friction." The angle of repose * (tan ♦ = F/N) is the angle at which the 

 plane must be tilted before the object will move from its own weight. The following table of coefficients was com- 

 piled by Rankine from the results of General Morin and other authorities and is sufficient for ordinary purposes. 



* Quoted from a paper bv Jenkin and Ewing, " Phil. Trans. R. S.' - vol. 167. In this paper it is shown that in 

 cases where " static friction " exceeds " kinetic friction " there is a gradual increase of the coefficient of friction as the 

 speed is reduced towards zero. 



TABLE 167.— Lubricants 



The best lubricants are in general the following: Low temperatures, light mineral lubricating 

 oils. Very great pressures, slow speeds, graphite, soapstone and other solid lubricants. Heavy 

 pressures, slow speeds, ditto and lard, tallow and other greases. Heavy pressures and high speeds, 

 sperm oil, castor oil, heavy mineral oils. Light pressures, high speeds, sperm, refined petroleum 

 olive, rape, cottonseed. Ordinary machinery, lard oil, tallow oil, heavy mineral oils and the 

 heavier vegetable oils. Steam cylinders, heavy mineral oils, lard, tallow. Watches and delicate 

 mechanisms, clarified sperm, neat's-foot, porpoise, olive and light mineral lubricating oils. 



TABLE 168. — Lubricants For Cutting Tools 



Tables 167 and 1 

 Wiley and Sons. 



Smithsonian Tables 



Mixture = l{ crude petroleum, % lard oil. Oil = sperm or lard, 

 quoted from " Friction and Lost Work in Machinery and Mill Work," Thurston, 



