THE TECHNOLOGIST. [Sept. 1, 1864. 



60 ON THE MACHINERY FOR 



tioa clutch for throwing in and out of gear. On the top of the spindle 

 is a wrought-iron arm or crank carrying a movable stud, which works 

 with a bush in the centre of the fly frame. Round the centre spindle 

 are also four other spindles equidistant from the centre spindle, and 

 from one another, each carrying on the top a wrought-iron arm or crank 

 with movable stud, similar to the centre one ; these studs severally 

 work in bushes at each corner of the fly frame. Hence, when motion 

 is given to the centre spindle, the fly frame is carried round by the stud 

 on the crank arm, while its sides are always kept parallel to their 

 original position by the four corner cranks. The two runner frames 

 being connected by their central stud to the arms of the fly frame, 

 receive the same circular motion as the fly frame ; but at the same time 

 they are left free to revolve round their own centres, which they do in 

 a greater or less degree, according to the varying friction of the grind- 

 ing surfaces. The grinding motion being thus obtained, sand and water 

 are constantly applied, until the surface of the glass is found upon 

 examination to be free from all defects ; the sand is then washed off 

 the glass, and the first stage of the smoothing process is commenced on 

 the same machine by substituting the coarser qualities of emery in 

 place of the sand. The plate of glass is then removed from the bench, 

 turned over and replaced on the bench, and submitted to the same 

 process on the other side. The speed at which the fly frame is driven 

 is about forty revolutions per minute. As the runner frame is not suf- 

 ficiently large to act upon the entire surface of a large plate of glass at 

 one time, it is therefore necessary to divide the operation, and shift the 

 position of the runner frame as the work requires it, by inserting the 

 centre stud of the runner frame into a different portion of the slot 

 between the fly frame bars. 



Until the last few years the principal part of the operation of 

 smoothing was effected by manual labour, the operation being per- 

 formed by rubbing two pieces of glass together, and applying emery 

 powder between them. Great care is requisite as the work approaches 

 completion, that no scratching shall take place ; and it is on this 

 account that hand labour is considered absolutely necessary for finish- 

 ing the process, the slightest scratch being immediately felt by a prac- 

 tised hand, whilst a single stray particle of grit on a machine would 

 spoil the whole surface before it was perceived. About 1857 Mr. Cross- 

 ley introduced a machine for smoothing the plates of glass, which so 

 far succeeded that the nicety of the hand touch is only required for the 

 final part of the operation. This smoothing machine is exceedingly 

 simple and inexpensive, consisting of a long wooden bar connected at 

 one end to a crank, or an upright spindle, and extending over the stone 

 bench on which the plate of glass is laid : two runner frames of wood 

 are attached to the bar, and on the underside of each frame is fixed 

 another plate of glass ; these are then laid upon the glass on the bench. 

 In this case the runner frames are only allowed to partake of the 



