ON CUTTING GLASS. 



267 



edges of the covers, whether circular or otherwise, are not cut 

 sufficiently well to allow of the fragments being separated 

 from them readily, but little pieces of glass are left behind, 

 a fine file rubbed over the edges, will make them smooth, 

 and any of the cements will adhere more firmly to them. 

 For this purpose the cover should be held between the thumb 

 and first finger, and only a small portion of the edge allowed 

 to project above the fingers for the file to act on at a time ; 

 by these means there will be but very little risk of fracture. 



The methods above described are very useful when the 

 operator is in possession of a writing diamond only ; but the 

 following very ingenious instruments have lately been con- 

 trived for the express purpose of cutting 

 circular covers. The first of these is the 

 invention of Mr. Shadbolt, and is repre- 

 sented in fig. 171. It consists of a cen- 

 tral stem of steel wire, a a, sliding freely 

 in a tube of brass, b. To the upper end 

 of the wire is attached a disc of ivory, c, 

 and to the lower a small cylinder of box- 

 wood, d; to the lower end of the tube, b, 

 is fastened a piece of brass, e, through 

 which is made to slide a small triangular 

 bar,^ carrying at one end a semicircular 

 piece of brass, ff, through which slides a 

 steel pin, h, armed with a diamond point; 

 j7i. V§>^ *^/ the pin may be fixed at any required 

 height by the screw, i, and the bar also 

 (when regulated for the size of circle to 

 be cut) by the screw,,/. The use of the 

 instrument is obvious, the cylinder, d, being placed in an 

 upright position upon the piece of thin glass, and the arm, /, 

 adjusted to the required size of the cover to be cut, a finger 

 of the left hand is to be placed upon the disc, c, and one of the 

 rio-ht upon the edge of the larger disc of wood, k ; if this last 

 be revolved, it wiU carry with it the arm, bearing the diamond, 

 and a little practice will enable the operator so to regulate the 

 pressure of the latter upon the glass, as to make a perfectly 



Fig. 171. 



