Journal of the Society of Motion Picture and Television Engineers (1950-1954)

from defects. Two bands were left on the sides of the disk for removal of material to correct unbalance. These bands were not utilized, however, because balancing equipment sensitive to an unbalance of 0.1 oz-in. showed no sign of unbalance. The calculation of disk stresses was in accordance with the method outlined by Timoshenko. Computations started with the centrifugal force exerted by the prisms, and worked back toward the axis in six concentric bands. These calculations showed that the tangential stress at the bore, which was the maximum stress, was 25,000 psi for a spin rate of 12,000 rpm. Two critical speeds were determined mathematically, at which forward or retrograde precessions should have rates identical with the rate of spin of the disk. The results indicated a critical speed for forward precession of 41,200 rpm, and a critical speed for retrograde precession of 4165 rpm. Although the critical speed of 4165 rpm for retrograde precession is within the operating range of the camera, no difficulty has been encountered upon acceleration of the disk through this speed. No difficulty, in fact, was expected. The photosensitive film is held in proper position, on each side of the spinning disk, by a series of 50 aluminum pegs, one for each tenth perforation of the film. An overlap of several frames is allowed when the film is cut to proper length in the darkroom. The strip of film is brought to the camera coiled in a light-tight container, and is placed in the camera through handholes in the housing few the spinning disk. The disk is readily turned by hand as the film strip is fed through a handhole and pressed onto the pegs one at a time. The direction of loading is the same as that of operation, so that the trailing end of the film overlaps the leading end. Centrifugal force ensures that the emulsion is in the focal plane during exposure. The disk is mounted on the over hanging end of a 2-in. shaft. It i: pressed onto a taper, is secured by twq nuts, and is driven by a face-type key The shaft rotates in a pair of Class "/ precision ball bearings. The preload in these matched bearings is produced by clamping with inner and outer spacers of identical length. Service is so intermittent that no heating problem is involved. Adequate lubrication is provided by three drops of high-speed bearing oil inserted into the vacuumtight oil tube each morning. Labyrinth seals prevent passage of oil into the housing of the spinning disk. Ground helical gears are used between the hydraulic piston motor and the shaft of the spinning disk, and between that shaft and that of the tachometer generator. The housing for the hydraulic piston motor and the tachometer generator was fabricated of Meehanite castings. It is vacuum-tight and is pierced by the hydraulic lines, electrical leads for the tachometer, an access plug for lubricat-l ing the tachometer, and a tube for I insertion of gear grease. The housing j for the spuming disk and its cover were) cast of an alloy steel with a yield strength of 100,000 psi. Alignment of the! bearing housing and of the optical mounting pads at the periphery of this housing is ensured by five deep ribs. The peripheral surface of the housing is 1 in. thick, to provide some protection against possible failure of the disk. All of the optical components excepting those on the spinning disk are mounted in the housing or upon brackets attached to the housing. The cover of the] housing of the spinning disk will serve as the principal support for the second optical system. Meehanite castings form the brackets for mounting of the mirrors in the optical systems. The top bridge supports the focusing mount for the objective lens, the external mirror for horizontal viewing, and, on its underside, the mirror located in the optical path from^ 140 February 1953 Journal of the SMPTE Vol. 60