By this method of balancing, the wheel will remain in true balance notwithstanding its wear, because the balancing proceeds equally from the perimeter towards the centre of the wheel.
Fig. 2017.
Emery Grinding Machines. (For grinding-lathes and roll grinding, see [article on Lathes].)—[Fig. 2017] represents Brown & Sharpe’s grinding machine. The bed, the table, and the cross-feed motion of this machine closely resemble those of the planing machine, but its work is far more smoothly and accurately done than can be performed in a planing machine. The table traverses to and fro, accurately guided in ways, and the revolving emery wheel takes the place of the ordinary cutting tool, being carried in a sliding head upon a cross slide or cross bar. The drum for driving the emery wheel is at the back of the machine, as shown in the cut.
Fig. 2018.
The vertical feed motion for adjusting the depth of cut of the emery wheel is capable of very minute adjustment, thus avoiding a difficulty commonly experienced in iron planing machines on account of the coarseness of feed-screw pitch, which coarseness is necessary to insure their durability. The means by which this capability of minute adjustment is effected is shown in [Fig. 2018], in which d is the cross head of the machine and c the sliding head having the arm c′, which provides at b a pivot for the wheel-carrying arm a. f is a stud fast in c and carrying e, which forms the nut for the feed screw. Outside this nut is the spiral spring s, whose force steadies the upper end of a.
Now suppose the feed wheel g be operated a full rotation, and the motion of that end of a will be that due to the pitch of the feed screw, but the motion at the centre h of the emery wheel will be the pitch of the screw divided by the difference between the length from the centre of h to the centre of the feed screw, and that from the centre of h to the centre of b. But even this diminished motion at h is still further reduced, so far as the depth of cut put on is concerned, because the motion of h is not directly vertical but an arc p, of which b is the centre.