1030

THEORY AND PRACTICE OF ENGINEERING.

Book II.

block under the bed of the lathe, where its end, with a screw cut upon it, receives a nut:the rest may be turned in any direction, but is fixed in its place in a similar way to theback puppet; the front puppet is also securedby a screw and nut, and has a motion along thebed when required: the chucks, formed of brass,are tapped and screwed on to the mandrell, witha hole in each to receive the wood to be turned.

Previous to the application of the slide restto the lathe, the tool was held by the work-man and entirely guided by his skill, and inturning the shaft of a column, it was scarcelypossible that his unaided efforts could bring thewhole into the true frustum of a cone, or thathe could set out the swell or entasis at a certainportion of its height with the requisite precision:but when the principle of sliding the rest whichheld the tool for cutting was introduced, theshaft could be turned with extraordinary correct-ness: the cutting instrument in this new arrange-ment is held firmly and securely, and made toprogress in a definite direction by means of aslide, the motion being communicated by ahandle that turns a screw : two such slides pro-duce a motion along as well as across the work,and so nicely is this arranged by turning thescrew handles, that it is scarcely requisite tolook at the operation as it goes on.

Mr. Henry Maudsley contrived a self-actingslide rest , which has produced great improve-ments in every kind of machine : a piece of ironis attached to the work at one end, and turnsround a star wheel at the end of the screw that moves the rest, which at each revo-lution of the lathe turns the screw and moves forward the slide rest, which carries the

Fig. 1577.

Fig. 1578.

SLIDE BEST,

tool onwards by degrees until the whole is very accurately turned, without the constantattendance of the workman. This ingenious contrivance has been applied, as we shall here-after see, to a variety of other purposes.

Drilling machine is far more serviceable than the ordinary bore, and indispensable whenthe heavier kinds of iron work are to be drilled. The winch or handle is carried by twostandards, and may be turned by three men ; this, by means of a bevelled wheel, turnsanother placed horizontally, through the centre of which the drill shaft passes freely, anddescends as the drilling proceeds. The drill at top, surrounded by a collar, is worked bya rack and small pinions attached to another wheel, over which passes an endlesschain, which when pulled raises the rack and drill shaft; it is supported by a ratchet-wheel