on the keys are quite sufficient to rupture them.

Mr. Brunel, in the government saw-mills at Woolwich, adopted a method
of hanging saws by means of a weighted lever, like a Roman steelyard.
A cross-shaft affixed above the saws to the cornice of the main frame
carried a lever, weighted at one end and provided with a hook or shackle
at the other for engagement with the saw buckle. In using this apparatus
the blades were strained one at a time by linking the lever to the
buckle and then adjusting the movable weight until the desired tension
was acquired, after which the key was inserted into the mortise and the
lever released. This arrangement is not now in common use on account of
the trouble attending its employment, and at present the saws are merely
strained by hammering up the keys. The saw blades had usually a tensile
strain of upwards of one tun per inch of breadth of blade. It is to
be further observed that the cutting edges of the saws are not quite
perpendicular, but have a little lead, or their upper ends overhang the
lower about three eighths of an inch or one half of an inch, according
to the nature of the material to be sawn. The object of this is that the
saws may be withdrawn from the cuts in the ascending or back stroke, and
allow the sawdust free escape. The eccentric actuating the mechanism for
advancing the timber to the saws is generally set in such a manner that
the feed commences just at the moment when the frame has attained half
its ascending stroke, and continues until the entire stroke has been
completed. By this regulation the saws are not liable to be suddenly
choked, but come smoothly and softly into their work.--_Worssam's
Mechanical Saws_.

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