CHAPTER XII.

GRINDING THE ACCURATE AND RAPID GRINDING OF TOOLS AND SMALL MACHINE PARTS-EMERY WHEELS.

Cutter and Tool Grinding.

A subject germain to the treatment of steel is that of grinding, as in most lines of steel working it occupies an important position. In the following are shown illustrations of approved machines for the grinding of fine tool work and accurate small machine parts. Descriptions are also given of the correct methods of grinding the different tools and parts.

The machine illustrated in Fig. 146 is of a type used extensively for general toolroom work and is one of a class of universal cutter and tool grinders which has been greatly improved and developed during the last few years. It may be used to grind accurately and rapidly work of the following kinds and sizes:

Milling machine cutters 12 inches in diameter when not more than I inch wide.

Work 14 inches long held between centers when the diameter of rotation is not more than 8 inches. These dimensions are given as the limit for irregular pieces and not for heavy, solid cylinders.

Work 14 inches long can be ground by using an emery wheel on each side of the head.

Reamers and shell counterbores of large or small sizes.
Gear cutters and formed cutters of every description.
Flat surfaces, such as shear plates, dies and gages.

Hardened bushing and other pieces to be ground internally. Conical surfaces, such as taper bearings and mandrels, and small cylindrical machine parts which are to be finished with extreme accuracy.

The foregoing list does not give the limit of the capacity of machine, but rather indicates in a general way what is possible in its use.

For a more particular presentation of the kinds of work which can be and are actually ground on such machines, reference is made to the following pages.

Prominent Features.

Those familiar with grinding the side teeth of side milling and angular cutters are aware that the tooth rest must be set to the exact height so as to bring the cutting edge of the tooth to be ground in an exact parallel line with the slide. In some machines

this adjustment of the tooth rest for this grinding is complicated. The difficulty, however, is overcome in this machine, as no attention is required to adjust the tooth rest, since it is centrally fixed for all diameters of cutters. The tooth rest travels with the cutter, except in the grinding of spiral mills and large saws.

GRINDING.

3

The side teeth of angular and side milling cutters are ground off with practically a straight line clearance. This is done with a cup-shape emery wheel 3 inches in diameter on the left side of the machine. The advantages of grinding side teeth with a fair size emery wheel, and at the same time grinding a straight line clearance with an accompanying strong cutting edge, are known to those who have heretofore been compelled to use a small wheel grinding a hollow clearance and weak-cutting edge. (See Fig. 149.)

To prevent the drawing of the temper from cutting edges of side mills and the side teeth of angular cutters, etc., which have a

FIG. 149.-GRINDING SIDE TEETH.

broad surface, it is important that the heel of the tooth be stocked out first at a sharp angle, and only a small portion left to be ground at a different angle. The change from stocking out to the grinding of the cutting edge is quickly made by moving the knee a few degrees around the column.

This feature of revolving the knee around the column has also the following advantages:

Work can be brought in contact with the emery wheels on either side of the wheel without rechucking. Also the article to be ground can be brought in contact with the emery wheel in the most favorable position to either wheel for rapid grinding. For an example, a side milling cutter may have the outer teeth ground off on the straight face emery wheel on the right side of the ma