wheel is brought in contact with the surface of the hole to be ground by adjusting the orbit (in which it revolves, and which orbit revolves) to the necessary extent, which is accomplished by increasing the eccentricity of the spindles, by means of the hand wheel shown on the drawing as Fig. 8. These movements are combined with an adjustable vertical reciprocating motion of the whole system of spindles, actuated by the crank, rod, and levers (Figs. 10, 22, and 24) for the purpose of traversing holes of various depths. When lapping out holes, a grinding wheel should be used of such a diameter as will enable it to pass freely through the holes about to be ground.

The eccentric orbit, in which revolves the emery wheel, is adjusted centrally with the hole by means of the transverse adjustment on the headstock (Fig. 3), and longitudinal adjustment on the main table (Fig. 4), this table having a fine adjustment with worm and wheel (Fig. 5), which is actuated by a clutch (Fig. 6). The correct position is found by inserting the grinding wheel in the hole and revolving the main spindle (Fig. 7), while at the same time throwing the internal spindle (Fig. 2)fficiently out of centre to bring the emery wheel in contact with the sides of the hole all round.

The feed is obtained by carefully increasing the eccentricity of the grinder spindle by turning the hand wheel (Fig. 8) at the top of the main spindle, which should be then fixed in position by means of the lock nut (Fig. 9). When gauging work is fixed on the machine table, the emery wheel can be raised out of the hole by liberating the connecting rod (Fig. 10 on drawing).

Grinding Expansion Links and Blocks. To grind expansion links and blocks, the grinder spindle is set concentric with the main spindle, and is locked in that position by means of a set-screw Fig. 13, the mandrel used for lapping holes being replaced by one having an adjustable lower bearing (Fig. 14). The main table remaining stationary, the supplementary table is guided between vee strips which fit into the grooves of the main table.

In grinding radial links and blocks, the above-mentioned strips are removed, and the table is bolted to the radius arm (Fig. 18), which must be set to the exact radius required.

In either case the stroke of the table must be accurately adjusted to suit the length of the link or block by means of the horizontal disc and connecting rod (Fig. 19).

In grinding slide-bars, &c., the large emery wheel is used (Fig. 20), the work being fixed on suitable chucks mounted to the main table, the longitudinal traverse being adjusted by means of the spring stops (Fig. 21), to suit the work being ground. The axle boxes are fixed on a chuck which swivels on a centre, bolted to the table, and is set square to the same by taper blocks sliding in the table grooves, and fitting into recesses in the end of the chuck. When grinding, a constant stream of clean water should be forced on to the emery wheel by means of the pump attached to the machine.

Grinding Shafts of Steel.-Grinding is superseding lathe work in some cases by removing a small amount from steel shafts, axles,

spindles, etc. Although the roughing has previously been done in an ordinary slide lathe with a cutting tool, it is found an advantage to use a grinding machine to get a more accurate finish on the work. There are occasionally small chilled portions in castings of iron, especially when the work has cores (which have been held in their place in the mould with nails). These small, hard points resist ordinary turning or boring tools, and are a source of trouble and delay if they cannot be cut out with hammer and chisel. If, however, an emery wheel is used, the obstructions can be removed in a few minutes.

Circular-saw Sharpening Machines.-There are two kinds of saw teeth (Figs. 241, 242). The former has teeth cut at equal distance apart around its periphery with a saw file. An improved form is shown in the latter case, being spaced and cut with a coarser pitch. This leaves the teeth much stronger, and at the same time gives ample space for the cuttings to fall away. The makers, Messrs. Spear & Jackson, state that

the improved form of teeth gives very satisfactory results, as no clogging The teeth are too hard to be sharpened by filing, but are easily

occurs.

and quickly ground by an emery wheel.

An automatic sharpening machine is shown in Fig. 243 with circular saw under treatment. This is provided with an emery wheel which has a uniform reciprocating motion, the saw being thus moved one tooth at a time, which movement is identical with that of the wheel. Therefore the grinding is regular, as each tooth is equally treated. In this respect automatic sharpening is valuable, because each tooth cuts with the same pressure.

Swing-frame Grinding Machine (Fig. 244).—This machine is suspended from overhead, and is fitted with universal joints and telescopic rods, so that the wheel may be twisted to any angle, or swung into range to work on the surfaces of machine beds and other heavy castings in the fettling shop, instead of chipping and filing them. In some cases a circular wire-scratch brush is used in place of the grinding wheel,

which quickly cleans the sand away and shows any projections to be smoothened down.

It is the practice to prevent as far as possible any loose portions of emery doing damage by covering the discs with suitable covering. This is seen to the full extent on an emery tool grinder, as in Fig. 190A, where only a small niche is left for the rest on which to place the tool while it is being ground. It should be pointed out that the percentage of flying wheels is very small, but when they do burst, owing to their

centrifugal force, they may do considerable damage if allowed to get away.

Keeping wheels in true condition is another and an important help against breakage. A systematic overhaul of each disc is adopted in many shops. There is much to be said in favour of this practice, which will perhaps be better understood if the faults of an untrue wheel are considered. A dull wheel has little bite. An eccentric wheel does not cut evenly; it is more likely to burst, and destroys the evenness of the spindle bearings, causing it to vibrate, and therefore unduly wear

away.

Polishing and Buffing. Small work, such as cycle and sewingmachine parts, are sometimes ground and polished on an emery band machine, such as is shown in Fig. 245. The belt or band is emery

FIG. 244.-Swing-frame grinding machine.

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covered, and is kept uniformly apart by passing over guide pulleys. Several operatives may be working at the same time at this machine. After the articles are polished they are finally finished on 'mops' and brushes. A mop or "bob" is made by securing a number of sheets of calico between two small washers of leather. The calico sheets are