1895.] Cutting, Grinding, and Polishing Section-plates, $c. 327 



Three interchangeable cutting discs are supplied, one of the usual 

 thickness of a lapidary's cutter, and two somewhat thicker, which 

 are preferable on account of their greater rigidity ; their edges are 

 carefully squared and charged with diamond dust in the usual 

 manner. In order to protect the instrument from particles projected 

 during cutting, the disc is surrounded, except in the vicinity of the 

 crystal, with a readily removable guard n. A second larger guard 

 is also supplied in order to afford more complete protection to the 

 optical tubes ; it consists of a thin metal disc considerably larger 

 than the grinding table, upon which it is intended to rest, and fitted 

 round one-half of its circumference with a rim 1| in. high, sufficient 

 to protect the telescope and collimator, while not interfering with the 

 freedom of movement of the arm of the cutting apparatus. The 

 support upon the front pillar is removable when the cutter is not in 

 use, so as to leave room for grinding ; the pillar carries in front at 

 the convenient height a rectangular thickening o, out of which a 

 vertical dove-tailed recess is cut, within which a corresponding dove- 

 tail p, forming the back portion of the main casting of the attachment, 

 is capable of sliding until arrested at the proper height, corresponding 

 to the perfectly horizontal position of the cutter and its arm, by a stop. 



This attachment includes not only the supporting fork q for the 

 arm, but also the apparatus for directing and controlling the 

 cutting. The latter consists of a horizontal traversing bed r and 

 slider s, manipulated by the large milled head t of the traversing screw ; 

 the arm is attached to the slider by being gripped between a small 

 spring pistons and a hinged wedge-shaped hook w, the latter being so 

 shaped in order that it may be pushed out of the way while the arm 

 passes it, after which a spring x causes it to fall down behind the arm. 

 This gripping arrangement is carried by a much larger piston, retained 

 by a strong spring in a cylinder y fixed to the slider. The possibility 

 of undue pressure being developed between cutter and crystal, 

 owing to injudiciously rapid rotation of the traversing screw, is thus 

 avoided, the spring giving way before the pressure becomes danger- 

 ously great and the piston being pulled out of the cylinder. Two 

 inches of traverse are permitted by the length of the slot z of the 

 fork and of the traversing bed of the slider, an amount ample to permit 

 of the cutting through of a crystal an inch in diameter. 



This form of cutting apparatus is found to work admirably; 

 there is no tendency to jamming when once the operator has become 

 familiar with the rate at which the milled head of the traversing 

 apparatus can most advantageously be rotated, and the cutting is 

 more perfectly under control than when the pressure of the cutter 

 against the crystal is brought about by a spring or a weight hanging 

 over a pulley. 



The adjustment of the crystal, so that the direction of the desired 



