™ T ™ 



Figure 16. — Screw press, 1822, for expressing vegetable oils, such as 

 linseed. Restored patent drawing in Record Group 241 , National Archives. 



these wrought iron rest bars, was a slight groove. 

 From end to end in this groove was rolled a button 

 end hand tool with so long a handle that the operator 

 could rest it on his shoulder. I was often astonished 

 at seeing the long curled shaving turned off in this 

 primitive manner, and at the accuracy of the bolt 

 turned, when tested by straight edge and calipers. [13] 



After a number of bolts of the same size had been 

 turned, came the thread cutting, and this may be 

 considered an advance or evolution from haphazard 

 hand chasing and die cutting to the present engine 

 lathe work, and even at this day will be looked at as 

 an ingenious device. On the 3 inches of the over- 

 hanging back mandrel was slid up against its collar 

 what Mr. White called his "screw guide"; it was a 

 template screw of the diameter and pitch of the 

 screws he was about chasing, of about 4 inches in 

 length on its thread; the portion projecting beyond 

 the 3-inch overhanging mandrel was closed to a 

 square hole in its center, into which the tit heretofore 



described on the end of the screw bolt would loosely 

 fit. The carrying center of the back mandrel was a 

 round steel rod about 8 inches long, perfectly straight 

 beyond its pointed end. This center rod fitted in the 

 center of the back mandrel, and was driven forward 

 and held to its work by a wedge-key through a slotted 

 hole in the mandrel. When the bolt on which the 

 screw was to be chased was put in the lathe, the back 

 head was driven forward by the wooden keys so as to 

 bring it and the template firmly together; the back 

 center was then driven forward by the key through 

 the mandrel. By this arrangement the guide tem- 

 plate was made to revolve with the screw bolt. 



The chasing tool— or, rather, tool carrier — was 

 wrought iron, in form of a cross, with very short, 

 broad arms — in fact, they did not project more than 

 half an inch beyond the body. These arms were 

 grooved to carry the cutting tool and guide. The 

 end of this carrier next the work was much lighter 

 than the body, and was shaped so as to pass under the 



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