Janoaey 9, 1903.] 



SCIENCE. 



53 



The recent improvements in the manu- 

 facture of certain grades of tool steel have 

 shown indisputably that the present de- 

 signs of machine tools are not sufficiently 

 heavy to stand up to the work in order 

 to obtain the economy of operation which 

 results from the use of such steels. Higher 

 speeds, heavier cuts and greater feeds may 

 be obtained if the machines will stand the 

 strain, but in most cases the capacity of 

 the machine is not commensurate with the 

 ability of the tool to remove metal. With 

 cutting speeds of 100 to 200 feet per 

 minute, it is evident that the power re- 

 quirements will be much greater than for 

 the ordinary machines of to-day, which 

 have a cutting speed of from 10 to 30 feet 

 per minute. As an illustration of what 

 can be done with these new tool steels the 

 speaker was recently shown some steel 

 locomotive driving-wheels which had been 

 turned up in two hours and forty minutes, 

 whereas the regular time formerly re- 

 quired was not less than eight hours. In 

 this ease even better results could have 

 been obtained, but the belts would not 

 carry the load. 



Here then we find an interesting field 

 for the direct-connected motor with ample 

 power and speed variation for any work 

 which it may be called upon to perform. 



While the preference is easily given to 

 continuous-current motors for the pur- 

 poses of machine driving, yet we find al- 

 ternating current motors used to a con- 

 siderable extent, the proportion of motors 

 in service being about one to five in favor 

 of the continuous-current motor. Both 

 synchronous and induction motors are em- 

 ployed, but the advantages possessed by 

 the latter cause this type to be preferred, 

 although in long-distance transmissions, 

 both types should be used in order to ob- 

 tain satisfactory regulation. As shown by 

 Mr. H. S. Meyer,* the induction motor can 

 * London Engineering, April 19, 1901. 



readily be worked at variable speeds, which 

 is accomplished in three different ways: 

 (1) by rheostatic control, which is de- 

 cidedly the cheapest and easiest method 

 to manipulate; (2) by varying the im- 

 pressed voltage, which, however, necessi- 

 tates the use of a transformer or, compen- 

 sator with variable ratio; this is very in- 

 efficient at the lower speeds and can only 

 be used under certain conditions; and (3) 

 by altering the number of poles, which is 

 mechanically very complicated, but where 

 the speed variation is only one half or one 

 quarter, it may be used efficiently. 



One serious disadvantage met with in 

 all induction motors is the lag produced 

 by self-induction, and its reaction on the 

 circuit. This lag is particularly unsatis- 

 factory with intermittent service, such as 

 machine driving, where the motors have to 

 run under light and variable loads; in 

 such cases the power, factor is probably 

 not over 60 or 70 per cent. 



Reference has been made to the use of 

 compressed air and its facility of adapta- 

 tion to various requirements, but it is 

 evident from an inspection of some of the 

 devices in use that enthusiasm for new 

 methods, rather than good judgment, has 

 controlled in many of its applications. 



For some years compressed air was used 

 only in mines, where it produced marked 

 economies in underground work. Later, 

 compressed air was introduced into manu- 

 facturing lines, and to-day its use in rail- 

 road and other machine shops, boiler 

 shops, foundries and bridge works is being 

 widely extended. In the Santa Fe Rail- 

 road shops at Topeka there are over five 

 miles of pipe in which compressed air is 

 carried to the different machines and labor- 

 saving appliances throughout the works. 



In such shops air is used to operate rivet- 

 ing machines, punches, stay-bolt breakers, 

 stay-bolt cutters, rotary tapping and drill- 

 ing machines, flue rollers, rotary grinders, 



