iJSErf. 
1(;5 
( nier3^-wheei companies are prej^ared to make, I ran not do better 
than to mention AA'hat I saw and what was tohl me at the works of the 
Xorton Emer}^ AVlieel Company, at A^^orcester, Mass. The wheels are 
manufactured for the special work for which they are intended, and 
N'ary in shape, in bond, and in grain of corundum. The sizes of 
corundum that are used are Nos. 12, 14, 1(), 20, 24, 80, 80, 40, 50, 54, 
CO, 70, 80, 90, 100, 120, 150, 160, 180, 200, and G grades of flour corim- 
dum. The bond has 26 degrees of hardness, represented by the letters 
of the alphabet, although a bond is seldom used softer than E or 
harder than M. There are 408 different sizes of circular wheels, 
so that the diiferent grades of wheels possible are almost unlimited. 
(See figs. 25 and 26.) 
Fig. 25. — Emery and corundum wheels and stones adapted for all kinds of abrasive work. 
There are three types of wheels known to the trade — vitrified, 
chemical, and cement — the names being derived from the process by 
which they are manufactured. In the manufacture of all, the corun- 
dum or emery used is in grains of uniform size, but varies with the 
grade of wheel that is to be made. The vitrified wheel is the most 
important and most generally used, although for some work one of the 
others is preferable, and for very large wheels the chemical is espe- 
cially adapted. 
VITRIFIED WHEEL. 
In the manufacture of this wheel more care is necessary in the 
selection of the corundum, for in the vitrification of the bond foreign 
minerals containing water are very likely to cause the wheel to burst. 
