736 THE KAMSDEN DIVIDING ENGINE. 



" Several different arbors of tempered steel are truly ground into the 

 socket in the center of the wheel. The upper parts of the arbors that 

 stand above the plane are turned of various sizes, to suit the centers of 

 diiferent pieces of work to be divided. 



" When any instrument is to be divided, the center of it is very exactly 

 fitted on one of these arbors, and the instrument is fixed down to the 

 plane of the dividing wheel by means of screws, which fit into holes 

 made in the radii of the wheel for tliat purpose. 



" The instruments being thus fitted on the plane of the wheel, the 

 frame which carries the dividing point is connected at one end by finger 

 screws with the frame which carries the endless screw ; while the other 

 end embraces that part of the steel arbor which stands above the instru- 

 ment to be divided by an angular notch in a piece of hardened steel ; 

 by this means both ends of the frame are kept perfectly steady and 

 free from any shake. 



" The frame carrying the dividing j^oint or tracer is made to slide on 

 the frame which carries the endless screw to any distance from the cen- 

 ter of the wheel as the radius of the instrument to be divided may re- 

 quire, and may be there fastened by tightening two clamps, and the 

 dividing point or tracer being connected with the clamps by the double- 

 jointed frame admits a free and easy motion towards or from the center 

 for cutting the divisions without any lateral shake." 



ENGINE BY WHICH THE ENDLESS SCREW OF THE DIVIDING ENGINE 



WAS CUT. 



The machine constructed by Eamsden for cutting the screw, and 

 used to cut the 2,160 teeth in the circumference of the circle of his 

 dividing engine, is of the greatest interest, for it is one of the earliest 

 applications of the principle of changing the lateral speed of the tool 

 in cutting a screw by differential wheels; — the method now used in the 

 slide rest of a lathe. 



Plate III is from a photograph of this machine deposited in the U. S. 

 National Museum by Dr. Morton. 



It has not been found practicable to letter the various parts of this 

 machine to correspond with those referred to in Eamsden's description. 



It is believed however that the reader will find more interest in 

 following the original description in the words of the celebrated 

 mechanician than in reading an explanation of the construction of the 

 machine couched in modern terms. 



Ramsden describes his machine thus : 



A represents a triangular bar of , steel, to which the triangular holes 

 in the piece B and C are accurately fitted, and may be fixed on any 

 part of the bar by the screws B. 



J5 is a piece of steel whereon the screw is intended to be cut, 

 which, after being hardened and tempered, has its pivots turned in 

 the form of two frustrunis of cones, as represented in the drawings of 

 the dividing engine (foot-note Fig. 5). These pivots were very exactly 



