nearly all head-blocks there is provision for holding the balk or cant by its side at several places in its length. The " mill-dogs" II, fig. g), or devices by which the log or cant is firmly held to the head blocks, are so called because they hold by teeth or tooth-like projections, which bite into the timber, being either driven in by a maul or pressed in by a lever, cam, eccentric, or screw. Frozen logs require specially strong dogs.
Saw saw and its arbor may have as accessories the devices for giving " lead "—that is, a slight angle between the plane of the saw and the line of motion of the carriage—guides, to keep the disc from swerving, and the spreader or splitter, to keep the board just cut from touching the disc and to lessen friction. Lead is best given by adjusting the bearings of the saw-arbor.. The guide should have rapid adjustment for saws of different dimensions, and its jaws should be movable independ ently of each other and while the saw is in motion and the mill running. The mandrel should have its end play regulated from the middle. The splitter-wheel should not be upon any axis which bears a roll on which the lumber rests. There should be opposite and nearly touching the saw-plate cast-iron bearers or supports, to hold short pieces as they drop from the saw, and to prevent bits of bark, splinters, or slabs from wedging in against the saw. In gigging back on band-saw mills the saw may be deflected automatically or by a foot-lever. The mandrel should have one collar fixed and the other removable; these collars prevent end-wise mo tion. The saw or plate is held between two flanges, through which and the disc pass two bolts. The boxes of the mandrel should be of great length. To cool the saw or to prevent it from heating, the mandrel is sometimes made hollow, so that a current of water can be passed from one end to the other and ejected through the collar. Sometimes one end of the mandrel of a small machine is arranged to receive an auger-bit.
The Resaw, which is used for dividing thick boards into thinner ones, should be very thin, that it may cut a narrow kerf; for this purpose it is often made segmental, thin rim-segments being screwed to a thick centre piece and dovetailed to one another. The feed is by vertical rolls, which should be so arranged that if desired they will bring all the pressure to bear upon either side of the board. To prevent the collar from splitting the lumber ahead of the saw, a board of the requisite width, on top of which the lumber may be fed, may be put between the rolls before the saw is ranged, so that only enough of the disc shall be presented to make the cut. Resaw frames are best made with the ends open, so that the plate may be rolled out instead of being lifted.
saws may move either the saw and its mandrel or the stock; in the former case the saw may be swung, or it may be on ways. In the latter case its path is usually horizontal, and such machines arc commonly called " railway " saws. They may be mounted in a regular frame or may he hung in brackets, as is most convenient. A very useful and popular machine is the carriage cut-off, which has a stationary table at the left of the saw and a travelling carriage at the right, for emitting Some cut-off saws are swung in loops, and these arc best bored and fitted carefully upon each end of both the counter-shaft boxes, by which mean,; the cause of wear upon the counter-shaft is removed and the shaft relieved from the weight of the swinging frame.
Circular " edger " is a gang-ripping circular saw for putting clean edges on boards which have been sawed from round cants, and for ripping wide unedged boards into- narrow ones. This machine is a potent factor in saw-mill economy. A wide board may have in it two grades, and the edger-operator may by good judgment so divide it as to give two boards (one of high and the other of low grade) worth more than the one wide board. In gang edgers of recent construction (/5/. 12, fig. 2) the saws are moved upon their arbor b•hand-wheels at the front end of the table, convenient to the operator, and are so arranged that two saws may be locked together 6, 8, to, etc., inches apart, and so move together or separately as desired. With the most recent power-feed single saw edger the operator may send stock past the saw and return it without changing position or leaving his place. Where only wide boards are sawed, edgers should have rolls of the full width of the machine. For narrow stuff the rolls are broken in their length, whereby two boards of different thicknesses call be handled at once without difficulty. An effective edger for straight work should be provided with two sets of live feed-rolls, and also with hack feed-rolls. Some not only have their feed-rolls grooved lengthwise, but also have the back roll cut on its periphery, so as to form a kind of teeth, which serve to keep the lumber straight as it goes through, thus avoiding the tendency to follow the grain. In some gang edgers all the rolls are driven, the return roll upon the top having a reverse inotioi#, thereby feeding instead of shoving back the lumber. There is a rack upon the front extension, between the two front rolls, to prevent the boards returned over the top of the machine from getting down under the rolls. In one form of this machine one end of the arbor is carried in a bridge-tree, which may be readily removed, so that all the saws may be slid off.