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659 HANDBOOK OF PROJECTION FOR
which 8 is a pulley driven by a belt connecting with the projector mechanism, 1 is a shaft upon which this pulley rides. Pulley 8 is not attached to the shaft, but revolves freely thereon. Six is a cast iron disc attached to shaft 1 by means of a pin or set screw, so that the two must revolve as one member. Thirteen is the key which locks the take-up reel to shaft 1, and part 2 is the lock which holds the reel on the shaft. Between pulley 8 and disc 6 is a w*asher, 7, made of fiber. The action is as follows : Spring 12 is placed on the end of shaft 1 and against pulley 8. It is followed by collar 14 in which is a set screw. It will readily be seen that pulley 8, disc 6, and washer 7 will be clamped together by the pressure of spring 12, and that the amount of pull pulley 8 will exert on disc 6 through washer 7 before it will slip on washer 7 will depend upon the amount of pressure spring 12 exerts, which same may be altered by altering the position of collar 14.
This is the old style friction take-up; its trouble is that it must be set tight enough to revolve the reel under condition Y, which means that it will exert a very heavy pull on the film under condition X, Fig. 229. All the old style take-up did was to allow sufficient slippage between drive-wheel 8 and disc 6 to accommodate the slowing up of the reel as the film roll grew larger. This condition has the objections that it (a) tends to cause the losing of the lower loop, (b) it exerts an unnecessary and highly injurious strain on the perforations of the film, (c) it has a tendency to pull weak patches in two and (d) it has a very decided tendency to scratch the first hundred feet of film.
CAUTION. — Projectionists who are using old style takeups should be very careful to set the tension as lightly as is possible without danger of failure to rewind the entire film.
GENERAL INSTRUCTION NO. 24.— The projectionist will wish to know the exact ratio of intermittent speed employed by the various makes of projector, that being an important consideration when his opinion is asked by theatre management which proposes the purchase of new projectors.
Measuring the ratio of intermittent speed is not a very difficult matter, once the process is understood, but it nevertheless requires very careful, accurate work,, since a wrong conclusion, by even so much as two or three degrees, would be unfair to the projector or projectors it discriminated against unjustly.