22 TRUE SURFACES AND ACCURATE MEASUREMENTS ROBE. 



pressure of the upper plate is not sufficient to overcome the 

 capillary attraction, and force the oil out. It will at once be 

 recognized that this is the principle upon which all lubricated 

 bearings or journals of machinery, whether flat or round, are 

 constructed. This somewhat minute and elementary explanation 

 is given in order to show the importance of truth in the surfaces 

 of the bearings of machinery, to have flat bearings truly flat 

 and round bearings truly round. If such surfaces are uneven, 

 as they will be when made by the ordinary method of turning 

 or planing, owing to the springing of the cutting tools and 

 uneven texture of the metal, lumps will be produced which will 

 project through the oil, and the metals will touch each other 

 producing, when moving past each other at a high rate of speed, 

 friction and wear so common in machinery. But it has been 

 proved by experiment that, if the surfaces be made nearly true, 

 so that the lubricant will completely separate the metals, and 

 the bearing sufficient in area to withstand the weight imposed 

 without forcing the oil out, such journals may be run without 

 wear, and that the rate of speed, within practicable limits, makes 

 no difference. The question will at once suggest itself : Why 

 not make all the bearings of machinery perfectly true, suffi- 

 ciently large in surface, provide continuous lubrication, and 

 prevent wear entirely ? I may say that a very great advance 

 has been made in this direction. In the higher grades of 

 machinery, manufacturers use delicate grinding and scraping 

 processes to produce smooth and true surfaces, with the result 

 that many machines, such as electric dynamos and steam engines, 

 which run at a high rate of speed, have practically no wear in 

 their journals, but it is just here the mechanic learns how hard 

 it is to obtain absolute perfection. He may be able to produce 

 a sufficiently true surface, but he finds he cannot overcome the 

 distortion of metals, due to unequal pressure, or heat. As he 

 approaches greater refinement in producing true surfaces, he 

 will learn that it is impossible to get them to remain true when 

 subjected to the strains incident to the conditions under which 

 they work. He finds that, if he lifts his surface plate by one 

 corner it is less true, if I may be allowed the expression, than 



