THE 181
Tlie Shake.—For the purpose of closing up the fibres into a compact sheet
it is necessary to impart a sideways shake to the wire. This is accomplished by
a crank and shaft driven through cone pulleys so that the speed may be adjusted
to suit the stuff On old machines the frame of the wire at the breast roil was
supported on rocking standards.' The fault of this arrangement was that the
brasses of the crank, etc., had to withstand the shock of changing the direction
of the throw very suddenly and soon wore down and developed a knock.
An excellent shake motion (Fig. 64) is now manufactured by Messrs. James
Bertram and Sons Ltd.; in this the eccentric runs entirely enclosed in an oil
bath, and the wear in consequence is practically nil. This shake motion has
no cone pulleys, as it is driven by a variable speed motor.
On modem machines the frame is hung or supported on flexible steel
hinges or springs, so that the action becomes a soft swing, instead of a hard
jerk. About 1 to A- inch is an average length of throw, but it is a great advan-
tage to have an arrangement to allow of the length being altered, when running,
to suit different papers. A loose pulley or clutch is necessary to stop the shake
when the wire is not running.
The level or slope of the wire from the breast roll to the suction boxes
depends on the speed of the machine, and in some degree also on the quality
of the paper made.
Machines for high-speed work have the wire frame supported by adjiistable
standards, to alter the slope of the wire as the speed is put up. A machine
making newsprint at 1000 feet per minute may require a slope down from the
breast to the suction boxes of as much as 18 inches.
Slow-running machines making strong ledger papers from rags, with a
4O-Łeet wire, may need a rise of 2 inches from the breast to the boxes. A rise
of I to 11 inches on a 4O-feet wire making good-class water-marked papers
up to 120 feet per minute would be about right.