Figure 20. — A hob-grinding machine patented in 1932 and incorporating the master-screw 

 principle. Carl G. Olson's U.S. patent 1874592. 



new but had hitherto been solved by increasing the 

 size of the parts, an avenue of limited utility to de- 

 signers in these fields where total weight as well as 

 the effects of mass and inertia are so important. By 

 making these parts of heat-treated steel, the strength 

 could be made suitable while the size and mass of the 

 parts were kept within bounds. The necessary proc- 

 esses of heat-treating were not always applicable to 

 finished parts as they sometimes destroyed both finish 

 and accuracy. Grinding, which was well developed 

 for the simple plane, cylindrical, and conical surfaces 

 so widel) used in mechanisms, had to be extended to 

 threads and gears so that they could be finished after 

 heat-treating. Sometimes the gear teeth themselves 

 were ground; for other applications it was sufficient 

 to improve the accuracy of the gear cutters. 



Attempts to produce gear hobs free of the imper- 

 fe< tions and distortions introduced by heat treatment 

 I'll to another return to the use ol ilie mastei lead 

 screw. Figure 20 illustrates a machine having this 



feature which was patented in 1932 by Carl G. Olson. 6 

 In speaking of the spindle-driving mechanism dis- 

 closed in earlier patents, the patent goes on to say: 



I his driving mechanism includes an integral spindle 

 20, one extremity thereof being designed for supporting 

 a hob 22 and the other extremity thereof being formed 

 so as to present a lead screw 24. I he spindle 20 is 

 mounted between a bearing 26 and a bearing 28. the 

 latter bearing providing a nut in which the lead screw 

 24 rotates. . . . From the description thus far given it 

 will be apparent that the rotation of the lead screw 24 

 within the bearing or nut 28 will cause the hob to be 

 moved axially, the lead of the screw 24 being equal 

 to the lead of the thread in the hob. 



Claim 8 which concludes the descriptive portion of 

 the patent states in part : 



In a hob grinding machine of the class described, a 

 rotary work supporting spindle, means for effecting 



6 U.S. patent 1B7 1 r><>2, filed June «, 1929, issued to C G 

 Olson of Chicago, Illinois, August 30, 1932, and assigned to 

 the Illinois Tool Works, also of Chicago. 



1,1 III ll\ 240: CONTRIBUTIONS FROM Mil, MI'SFI'M OF HISTORY AND TFCHNOLOGY 



