LAPIDARY.

745

617

V

c

sSe

4r

i^fxF

u

*

a

"dth the one placed opposite on the other parallel face. These two pieces are calledsummers (lintels); the one placed at d is the upper; the one at r, the lower.

In fig. 617 this face is shown inside, in order to explain how the mill wheel is placeda ftd supported. The same letters point out the same objects, both in the preceding anddie following figures.

In each of these summers a square hole is cut out, exactly opposite to the other; in

__tl which are adjusted by friction, a square piece of oak a, a, fig.

617, whose extremities are perforated with a conical hole,which receives the two ends of the arbor H of the wheel i,and forms its socket. The square bar is adjusted at a conve-nient height, by a double wooden wedge b b.

The cross bar in the middle e supports the table c c, astrong plank of oak. It is pierced with two large holes whosecentres coincide with the centre of the conical holes hollow-ed out at the end of the square pins. These holes, of about6 inches diameter each, are intended to let the arbor passfreely through, bearing its respective wheel. (See one ofthese holes at i, in fig. 621 below.)

Each wheel is composed of an iron arbor h, fig. 618, of agrinding-wheel i, which differs in substance according tocircumstances, as already stated, and of the pulley j, furnish-ed with several grooves (see fig. 619), which has a squarefit upon the arbor. The 'arbor carries a collet d, on which\ are 4 iron pegs or pins that enter into the wheel to fastenit.

The wheel plate, of which the ground plan is shown at K,is hollowed out towards its centre to half its thickness ; whenit is in its position on the arbor, as indicated in fig. 619, awasher or ferrule of wrought iron is put over it, and securedin its place by a double wedge. In fig. 619 the wheel-plateis represented in section, that the connexion of the wholeparts may be seen.

A board g (see fig. 616 iinilfig. 624), about 7| inches high,is fixed to the part of the frame opposite to the side at whichthe lapidary works, and it prevents the substanc# made useof in the cutting and polishing, from being thrown to a dis-tance by the centrifugal force of the wheel-plate.

Behind this apparatus is mounted for each grinding-plate,a large wheel l (see fig. 616), similar to a cutler’s, but placed— horizontally. This wheel is grooved round its circumfer-

to receive an endless cord or band, which passes round one of the grooves of the^ lle y J, fixed below the wheel-plate. Hence, on turning the fly-wheel l, the plate re-f e * Ves w *th a velocity relative to the velocity communicated to the wheel l, and to the dif-. fence of diameter of the wheel l and the pulley J. Each wheel i, is mounted on an°,2 ar t>or, with a crank (see m, fig. 620:)

the lower pivot of that arbor h is conical, and turns in a socket fixed in the floor. The^ eat wheel i, rests on the collet i, furnished with its 4 iron pins, for securing the con-Xton. 'Above the wheel an iron washer is laid, and the whole is fixed by a double wedge.

w hich

enters into the mortise /, fig. 620.

Fig. 621 exhibits a ground-plan view of allthis assemblage of parts, to explain the structureof the machine. Every thing that stands abovethe upper summer-bar has been suppressed in thisrepresentation. Here we see the table c c; theupper summer m; the one wheel-plate 1, the otherhaving been removed to show that the endless corddoes not cross ; the two large wheels l l, presentin each machine, the crank bar n, seen separatein fig. 622, which serves for turning the wheel l.

622

bar is formed of 3 iron plates, n, o; p, q; and q, r; (fig. 622.) The first is