Before the log is put on, the travelling table is moved back, as shown in Fig. 1, 2, and the log is laid free of the saws on the batten, one end pressing against the head-stock, and the grapple teeth driven firmly into it. These keep the log steady under the action of the saws. The workman then moves the travelling table forward against the saws, till they have run through the log; he then returns the table to the position shown in the figures, removes the slabbed log and outside cuts, and is ready to begin to a fresh log.
The distance between the saws can be indefinitely varied between the width of the batten, which is the minimum, and the space between the side planks, which is the maximum.
The axle DKE, Figs. 5 and 6, is turned accurately cylindrical, and the 'launches, A, B, C, are drilled through in the centre, so as to allow them to be moved along the axle and no more. When the saw is placed at the desired point, a key is driven tightly in to a taper mortice made through the Haunches at K, which prevents the saw from shifting its position. The saws can also be changed by the same contrivance, and it is adapted to all the circular saws in this mill.
The next operation is, converting the slabbed log into deal. The slabbed log is laid flat on the side B (Fig. 6.) of the travelling table ABCD, the end of it against the head-stock H, from whose face a few sharp points stick out, which enter the end of the log, and keep it firm. For the first saw draft which takes off the round back, the log is set by the eye. The travel ling table is moved forwards as before, the back taken away, and the table returned to the position in the figure.
On the side D of the travelling frame is placed a guide G a few inches high, moving on parallel points, as shown in the figure, so as in every situation to con tinue parallel to the saw. This guide is set by the hand to the distance from the saw, equal to the in tended thickness of the deal, and kept in this situation by a ram's-head nut, as it is termed, screwed down tight on one of its points. The log is then placed with its face against the guide, and its end fixed to the head-stock as before. The table is moved forwards, and a deal of equal thickness cut off.
The way in which the saws are put in motion is shown by Fig. 7.
ABC is the spur-wheel, hung on the same axle with the water-wheel. The water-wheel is not shown. This spur-wheel works in a pinion BDE, on the same axle with which are hung as many drums as there are saw axles to be put in motion. Only one is shown in the figure, GEH. This drum turns by a strap, an inter mediate drum IKLM, which by another strap turns the pulley P of the same size, placed perpendicularly over it, on the axle of the saw.
The intermediate drum is hung in a frame, which is raised or lowered by means of a rack and pinion, worked by the hand in the mill above. The use of
this is to stop any of the saw axles, without stopping the machine; and the contrivance is very simple.
When the intermediate drum is raised to the situa tion i k l 7n, it is evident the strap NCLMI will only touch the intermediate drum in the points I.; and i, and consequently will not be put in motion by it; and the pulley P, together with the saw axle on which it is hung, will stop. The other strap GKLMII suffers so slight an alteration in tightness by the motion of the intermediate drum, that it turns it as before.
Fig. 8 shows the intermediate drum, its frame, and rack. The shaded part of the figure shows the grooved posts between which it moves. The pinion that works in the rack is not shown. It is put in mo tion by a capstane at the other end of its axle, and kept in the desired situation by a common catch.
Fig. 9 shows a contrivance for returning the travel ling table by the machine, which is more expeditious than the hand. AB an axle, set in motion by a strap from the principal drum axle on the fast pulley F. L a loose pulley on the axle AB, round which a rope is wound, passing over the roller R, at the end of the frame of the travelling table T, to which the rope is fastened. The loose pulley, when out of gear, as shown in the figure, allows the rope to be unwound freely as the table is moved forward. When it is to be put in gear, it is moved by the levers, C, D, E, G, H against the fast pulley, which carries it round by means of the iron knobs shown in the figure. The rope is then turned round the pulley, and the frame dragged back.
An improvement in the mode of fitting up circular saws was made by Mr. Maudslay. When the pivots at the end of the axle were conical, or when there were conical hollows on the end of the axles working upon fixed cones, the oil was always carried up the cone by the centrifugal force, and the sharp point being left without oil, soon heated, and caused the metal to be come soft. In order to avoid this, Mr. Maudslay made his saw spindles with double conical sockets, and the oil was introduced by a small hole into the smallest part of the double cones where they join. By this means the centrifugal force draws the oil into the fitting.
In order to prevent thin circular saws from bending, or buckling as it is called, they are confined between two flat circular plates: but in place of doing this, the bending is now confined to a more narrow ring near the rim of the saw. By this contrivance, the saw re volves with such truth and accuracy, that it is fit for the nicest operations, such as cutting the teeth of the finest cones. It is considered advantageous to soften circular saws when the teeth require sharpening, and to temper them only to a yellow colour. See Dr. Brewster's Journal of Science, No. III. p. 151.