The saw is here fed mechanically to its cut, whereas in some machines it is fed by its own weight, and therefore requires great care to be taken, when the saw is finishing its cut, in order to prevent it from falling after it has passed through the log.
[Fig. 3145] is a side elevation and [Fig. 3144] a plan of the machine, in which a is the frame of the machine on which are the bearings for the shaft b carrying the fast pulley c, loose pulley d and fly-wheel e at one end, and at the other, a crank disc f, whose pin is shown at g. This drives the saw k through the medium of the connecting rod h.
The saw is fast at the butt end to along slide j, j, which works in a long guide formed on the face of the swinging frame l, which pivots at one end on the shaft b and at the other is carried by a slide p, on the vertical slideway m, and is fed down the same to give the saw its cut by the screw whose hand wheel is shown at n.
v is a second guide for the saw, and being connected to the slide feeds down with the saw until it meets the log.
A counterweight w balances the weight of the slides and saw, so that there being a pit beneath the balance weight the saw and its guides may be raised so that the saw stands out of the way when not in use. y is a dog for holding the log, which is also blocked by the wedges z z′.
Fig. 3146.
The construction of the main bearing is shown in [Fig. 3146], in which it is seen that the hub or boss of the loose pulley is much longer than that of the fast one, thus providing a large amount of bearing surface, which is advantageous because the belt will remain longer at the loose pulley than it will on the tight one. The sleeves or bushes in which the shaft runs afford a simple means of renewal to restore the fit when the shaft has worn loose in its bearings.
It is obvious that as the guide frame l is pivoted to the shaft b, it carries the end of the saw (as it is fed down) in an arc of a circle of which the axis of b is the centre, whereas the slideway m is straight, and slide p therefore moves in a straight line instead of in the required arc. Provision however is made to accommodate these two motions as follows: