1034

THEORY AND PRACTICE OE ENGINEERING.

Book II.

guns, as the gun moves round, its exterior surface is turned quite true by means of a lathe.Musket barrels are similarly bored and turned bythe several motions of the common turning lathe,one machine finishing three barrels per hour.

The vertical boring machine, now generallypreferred, has the motion given to the uprightor drilling bar by three driving pulleys shown atc y the speed of which is regulated by the spur-wheels and pinions at d. When the drilling baris required to be lowered or raised, it is effectedby the spur gear at/, immediately above the nutt/y in which the screw works.

The plan of the machine shows a slide at ;n,which carries the work, and the table upon whichit rests is raised or lowered at pleasure by the racksand pinions at h,h, worked by the handle at o,which communicates with the spur-wheel andpinion p : within this is a ratchet-wheel. Inthe elevation at l, is a small lever or handle,for throwing the small clutch at k in and out ofgear, and the drilling bar is marked by e, t beingthe boring part of the bar, which can be made tobore a cylinder to the depth of 24 inches from£ an inch up to 14 in diameter. In some machinesan alteration of speed is obtained by means of twoshafts, one of which has a wheel working in apinion, and the other a pinion on a wheel.

A boring machine may be defined as con-trived for working a borer or tool, which, by arotary motion on its axis, cuts out a hollow’ cy-linder in any substance it is applied to; the whim-ble, the drill, the pulley, and the bow, are all ofthis class, but we now only use the term toan apparatus for boring large cylinders moreaccurately, and in shorter time than can be per-formed by manual labour. The method formerlyadopted for boring cylinders for pumps wasan horizontal axis turned slowly round by amill, at the end of which the borer was attached;the cylinder fastened to a carriage, made toslide in the direction parallel to its axis, wasdrawn forwards by means'of a weight that coulddescend. The defect of this system was theliability that the rectilineal motion of the carriagewould be transferred to the cylinder, and cause itto be bored improperly. Smeaton remediedthese evils to a certain extent, by introducing asteel-yard mounted upon a movable wheel car-riage, which traversed with the cylinder, and bysuspending the weight of the cutter and boringbar from it.

Machines for punching Boiler Plates with thegreatest possible accuracy are now made use of,instead of the ordinary punching machine, whichrequired the rivet holes to be marked out by atemplate with white paint, and afterwards broughtunder the punch : the plate is now affixed to the top of a movable table, ana when it isadjusted to the distance required between the rivets, the rest of the work is performedby machinery. In the Royal Dockyard at Woolwich, several of these punching ma-chines are at work in the shop where the steam boilers are wrought

The plate to be punched being laid upon the movable table at k, and secured by clamps,is brought over the die frame at i, where it is also directly under the influence of thepunch ; the whole of the machinery is mounted within a strong iron frame, and motion isconveyed to it by the tight and loose riggers at a,a, at the side of which is a fly-wheel forregulating it; on the spur-wheel at m is a tappet or pin, which, coming in contact with asmall lever, as the spur-wheel turns round, advances by a connecting rod the table shownat k , which runs along a railway provided for it by means of two carriages attached to the

Fig. 1584.

SIDE ELEVATION*