E will next consider the sash-bars which support the ridge of the roof and receive the glass. The total length which was required of these amounts to about two hundred miles; it will, therefore, be easily understood that mechanical contrivance for cutting them out became an absolute necessity; this Mr. Paxton appears to have discovered in his works at Chatsworth, as he mentions in his lecture.
MACHINE FOR CUTTING OUT SASH-BARS.
The sash-bars are one inch thick and one-and-a-half inches deep, and are grooved on each side, besides having all the four edges bevelled or chamfered; all which was done in one passage through the machine. The plank which was to form the sash-bars was passed in at one end of the machine, between pressure-rollers; it then passed between cutters placed both above and below it, which made about twelve hundred revolutions per minute, and hollowed out the different grooves; and, lastly, it passed between circular saws which divided it into separate sash-bars, after which they had only to be cut into their proper lengths.[[6]] The exact length of each sash-bar when finished is four feet one inch.
In this state the skylight bars were sent to the building, where they underwent several finishing operations, necessary to make the ends fit down into the notches prepared in the ridges and gutters. Thirty of the bars were first placed together in a horizontal traversing-frame on a saw-table, on each side of which circular saws were fixed at the distance of the required length of the sash-bar; the frame was then moved forward against the saws, so that both ends of the whole set of bars were cut off simultaneously, and at the same time a cut was made at one end half-way through the bar, in order to form the shoulder against the gutter. They were then removed to another bench, where the end of the bar was bevelled and the shoulder formed by means of a small instrument having a handle with two projecting jaws fitting into the ends of the glass grooves of the bars; between these there was a small blade which, being pressed down, cut out the shoulder which had been sawn through in the other direction, and another blade was placed at the proper angle to remove the bevelled piece at the end of the bar.
THE SASH-BAR DRILLING-MACHINE.
One more process made the sash-bars complete for fixing—this was the drilling a hole at each end to nail them down on the gutter and ridge; and this was also done by machinery, to insure all the holes being drilled at the same angle. On one side of a horizontal bench were placed a set of four-inch driving pulleys (a a), with as many horizontal drills projecting towards the other side of the bench; a wooden traversing-plate (c) opposite each drill, and working towards it, received one end of the sash-bar, while the other rested in an inclined position against a wooden rail (b) placed longitudinally above the pulleys, having as many sinkings thereon as there were drills. The traversing-plate being then pushed forward, the sash-bar was perforated by the drill; the plate was then drawn back, and the same operation repeated with the other end of the bar, which left it ready for fixing.
The action of the traversing-plate (c) is shown more distinctly in the second engraving.[[7]] One out of every nine of the sash-bars of the roof is stronger than the rest, to serve for fixing the ridge previous to glazing. These extra-strong bars are two inches wide and one inch and a half deep, and were formed by the same machinery already described, by an adjustment of the different cutters and saws.
