One of Mr. Brunet's saw-mills was constructed by Mr. Maudslay, for the arsenal at Woolwich. It is driven by a steam-engine; and the whole is considered as a pattern of the best, as well as the most elegant workmanship.
In this machine leather belts arc substituted most properly in place of cog-wheels; and in order to equalize the motion of the cranks in the most perfect manner, each crank has a fly-wheel attached to it, in dependent of the great fly-wheel of the steam-engine.
In the construction of the saw-frames Mr. Brunel has shown much ingenuity. They are all made of iron, but the sides arc left hollow, and are filled up with wood, in order to diminish the weight.
As it is of essential importance that the saws be placed parallel to each other, and stretched with the very same degree of tension, Mr. Brunel has effected this in the following ingenious manner. The saws are fitted into the frame, so that they can be quickly removed and replaced by sharp ones. Each saw has a piece of metal livened to each end of it, and formed like hooks. The hook in the lower end is hooked into a suitable recess in the lower cross bar of the saw frame, and the hook at the upper end seizes the hook of a shackle or link which hangs upon the upper cross bar, and has wedges through it, by which it can be drawn tight to strain the saw. As there is nothing to determine the parts of the cross-bars, where the hooks of the saws may hang, the saws can be set at any required distance from each other; but in order to retain them, pieces of hard wood are put in between the blades of the saws at the upper and lower ends; and '.-hen the spaces are thus filled up, they are kept tight by screws tapped in the sides of the saw-frames. Each saw is strained in succession by a steel-yard, con structed as follows: A strong axis goes across the fixed frame in which the saw-frame slides; and above the top of this frame from one side of this axis pro ceeds a lever, which has a weight fixed at the end, and from the opposite side of the axis proceed two short levers, which are connected by links with a strong cross bar, situated immediately above the upper cross bar of the saw-frame, when it has reached its highest elevation. Upon the steelyard cross bar is a shackle
or link, which can be united by a key with any of the shackles on the upper cross bar of the frame, which shackles, as we have already said, are united by their hooks with the upper end of their corresponding saws. By this means the lever with its weight becomes a steeelyard, by which any one of the saws may be drawn up with a given force.
In order to apply the steelyard, the frame is raised to its greatest height, and wedges are then put in be tween the top of the saw-frame and a fixed part of the stationary frame, so that the saw-frame may be kept fast when the steelyard is applied. The sharp saws are now put into the saw-frame by hooking them on the lower cross bar, and uniting the upper hooks to the shackles on the upper cross bar. The pieces of wood are then introduced between the saws, accord ing to the size of the wood, and they are bound fast by screws. The loaded end of the steelyard is now lifted up by a rope going over a pulley, su as to allow the link in the cross bar of the stcel-yard to be united with the shackle of one of its saws by its keys. The steelyard being now allowed to descend, it stretches the saw with a force depending upon its load. The 'wedge of the shackle for the saw is then thrust in by the hand as far as possible, so as to retain the saw at the tension given to it by the steelyard. The shackle of the steelyard is then disengaged from the saw and removed to the next, which is stretched in a similar manner.
In this saw mill, there is a contrivance by which each saw frame is allowed to retreat a small quantity in its ascent, in order that the teeth of the saws may keep quite clear of the wood when they ascend and do not cut.
Circular saws, or saws of a circular form, which cut during a continuous rotatory motion, have been used for cutting the teeth of watch and clock wheels since the time of Dr. Hook. They have been long used in Holland for cutting veneers, and they are said to have been introduced into this country by General Bentham. Mr. Taylor of Southampton, and Mr. George Smart, had the merit of introducing them very early; but we do not know the exact dates.