78 



At one end of the board forming the base of the machine is fastened, by 

 means of two hinges, a perpendicular piece of wood six and one-half inches 

 long, ciit so that there are three arms above. Each of two of these has an 

 opening at its upper extremity suitable for receiving the razor, and is pro- 

 vided with a set-screw for clamping the razor. 



To the third arm is attached a nut in which work the threads of a bolt, 

 which extends horizontally to near the axis. The head of the bolt is at- 

 tached to the centre of a wheel some four or five inches in diameter. The 

 bolt now forms the axis of this wheel and must be supported at the wheel 

 by an unyielding bearing. Turning this wheel once in the right direction 

 pulls the razor forward a distance equal to that between the threads, which 

 we shall suppose to be one-sixteenth of an inch. 



On the face farthest from the razor of the small wheel, about twenty 

 round brads are inserted near the circumference at equal distances apart, and 

 all the same distance fimn the centre of the bolt. If the wheel be rotated the 

 distance between two brads, the razor is drawn forward one three hundred 

 and twentieth of an inch. 



A small rectangle of tin or brass about three-fourths of an inch long is 

 bent at right angles, and one edge is cut to form a slightly concave set of 

 twelve vertical teeth of equal size, to turn the 4-inch wheel by pushing 

 against the brads. If ten of the teeth are used, one tooth will move the 

 razor forward one thirty-two hundredth of an inch. 



This ratchet is now fastened to the side of a long horizontal lever, which 

 is secured at one end to an upright support. The other arm rests upon an 

 eccentric on the square end of the axis of the 12-inch wheel. Turning this 

 wheel causes an up-and-down motion of the ratchet. The eccentric has a 

 rectangular opening so that it may be slipped upon the axis and made 

 more or less eccentric. It is held in any desired position by a set-screw. 

 A peg, or better a screw with the head removed, projects from the under 

 side of the lever just mentioned into a groove made in the circumference 

 of the eccentric. This groove must be so arranged, that when the ratchet 

 is rising, a tooth catches under a brad ; but when it ceases to rise, a short 

 oblique portion of the groove moves the tooth from under the brad. The 

 groove now resumes its straight course so as to prevent the next tooth 

 above from coming in contact with the brad as the ratchet descends. An- 

 other short oblique portion of the groove brings this tooth under the 

 brad. As one brad escapes from the top of the ratchet, another enters at 

 the bottom. 



