74
CONSTRUCTION OF TI-IE BUILDING.
“ of the Exhibition Building. The machine was first used in its present form in“ August 1838, and its original cost, including table, wheels, and everything com-“ plete, was 20/. The motive power is from a steam-engine employed on the“ premises for other purposes, and any well-seasoned timber may be used. The“ attendants required are only a man and a boy, and the expense of the power“ required for it when in use is comparatively trifling. The sash-bars may be“ made of any form, by changing the character of the saws. There is one par-“ ticular feature in working the machine, namely, that the bars are presented to“ the saws below the centre of motion, instead of above it, as is usual; and to the“sides of the saw which are ascending from the table, instead of those which are“ descending. These arrangements were necessary to suit the arrangement of the“ teeth to the grain of the wood; for when the bars were presented to the saws“in the usual way, the wood was crushed, instead of being cut and cleaned. It is“essential that the machine should revolve 1,200 times in a minute to finish the“work in a proper manner.”
SiLsh-bar machine We shall now proceed to describe the modification of this machine, which isBuilding. due to the inventive powers of Mr. Birch, of the Phoenix saw mills, near Cum-berland-market, Regent’s Park, with whom a contract was entered into byMessrs. Pox and Henderson for the supply of all the sash-bars for the roofthe upright bars for the vertical lights, and the ridges. Two of the principalpoints of difference between Mr. Birch’s machine and that described by Mr.PAXTON are, that revolving cutters arc substituted for saws, thus obviating diffi-culties incident to the grain of the wood; and that, by the addition of a second setof cutters, a plank passed between them is operated upon on its upper and undersurfaces at the same time. In fig. 25 is shown a cast-iron block (somewhat similarto those previously described in connection with the gutter-cutting machine), towhich are attached a variety of cutters. The rapid revolutions of the spindle (Afig. 26) operate upon the planks submitted to the action of the cutters, in themanner shown in fig. 28. bo soon as the plank, presented by the feed-roller, hasbeen operated upon by the rapid revolution of these miniature adzes, it is carriedon by the roller C, and is subjected to the action of circular saws of varyingdiameters, the lesser of which cut just sufficiently deep to form the groove for the