78 H. J. Grayson .• 



on enamel (which binds the diamond dust) to a thin vitreous coating 

 on the edge of the Avheel. The fusing process requires care, skill 

 and judgment. The wheel during the process is slowly revolved 

 and kept under observation with a magnifier. More than one coat- 

 ing of enamel will usually be required to ensure an enduring result. 

 It will be understood that this treatment does not injure or fuse the 

 diamond fragments, which, if small and uniformly graded, remain 

 .securely embedded in the enamel, filling the minute cavities of the 

 wheel edge. As the thin outer skin of the enamel wears away when 

 the wheel is in operation the diamond particles are exposed; hence 

 after a little preliminary use, the wheel edge when used for cutting 

 or grinding purposes which require prolonged endurance and i^er- 

 manence of shape, becomes the equivalent of. a diamond wheel. It 

 is, however, important that during is use, either upon hard steel, 

 glass, or any similar substance, the precaution not to overfeed or 

 force the rate of cutting be strictly observed. With due attention 

 to these precautions the " life " of the cutting edge of the wheel 

 may be greatly prolonged. The art of using such a wheel correctly 

 and effectively can only be gained by experience. 



The method of mounting and moving the ratchet head had next 

 to be provided for. The arrangements made for this purpose, also 

 for supporting and revolving the graduated circle and for main- 

 taining in a rigid position the two reading microscopes used upon 

 the circle, are sufficiently illustrated in the photograph, PI. XV. 

 This photograph, if carefully examined, is self explanatory in 

 respect to almost every detail. Some of the principal features 

 «hown therein, apart from the lathe and its fittings, are, first, the 

 «teel rod forming the spindle on which are mounted from left to 

 right in order — the ratchet wheel, next to this the tangent- wheel and 

 its fittings for moving and clamping the whole system during work 

 upon the ratchet. Finally the Watts divided circle for spacing and 

 controlling all angular movements upon the ratchet. The ratchet 

 wheel and divided circle were most carefully centred and correctly 

 related to each other by grinding the spindle on " dead " centres 

 and making full use of the two microscopes in the adjustment of the 

 reading circles. Once these adjustments were effected the ratcliot . 

 and divided circle were never displaced relatively to each other 

 during subsequent grinding operations upon the teeth. The micro- 

 scopes were securely mounted upon the tla-ust bar or socket of the 

 back centre which also provided for rotary swing and rough focus- 

 sing adjustment. Fine adjustments of the microscopes were effected 



