Motion Picture News (Jan-Mar 1917)

February 17, 1917 ACCESSORY NEWS SECTION 1111 iuiiiiiuiiiiioiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiuiiiiiiiiiiii^ THE CAMERA iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiHiiiiiniiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii^ The Manufacture of Cinematograph Film Stock (Continued from last week) THE methods of coating and drying cine films, as outlined in our previous chapters, are similar in all essential details, to those practised in preparing hand-camera films and photographic printing papers ; but when our roll of celluloid has been coated with emulsion and dried we come to a point of divergence from the procedure followed when preparing sensitized films and papers for ordinary photography. Following the removal of the coated and dried roll of film stock from the rewind of the take-down apparatus comes the operation of slitting up the large roll of sensitized film into narrow ribbons or strips of the dimensions required in the cinematographic processes. This is accomplished with speed and precision by the use of a " slitting machine," such as is shown in Fig. 3. The slitting machine shown in Fig. 3, is representative in appearance and operation, of all machines used in this class of work, and the machines used in slitting up the wide sheets of sensitive photographic film are similar or identical in design to those used in the paper-box industry for slitting paper into narrow ribbons. A study of Fig. 3, will readily make clear the manner in which a wide roll of coated film stock is divided into narrow bands by the slitting machine. After mounting the uncut roll on a suitable mandrel (or shaft) at one side of the apparatus the end of the celluloid sheet is passed between two rows of circular cutters, which latter are mounted on suitable spindles and revolve rapidly in opposite directions. Upon passing through these two rows of circular cutters or " roller shears " the film sheet is, of course, divided into bands or strips of desired width and then passes to the take-up (or rewind) spindles at the back of the machine. The slitting and rewinding machine shown in the illustration (Fig. 3) is the extremely efficient Knowlton slitter made by the M. D. Knowlton Co., of Rochester, N. Y. While designed primaril} for use in slitting paper the Knowlton machine (with some slight modifications) is also capable of high class results when used as a slitter for cinematograph film. There are numerous other slitting machines of high grade, but we have mentioned the Knowlton slitter because we are well acquainted with its capabilities in the particular line of work now being considered. Simple and automatic though it may seem, the operation of cutting a film roll up into cinematographic bands requires painstaking attention as do all other details in the manufacture of sensitized photographic materials. The rotary cutting wheels of the slitting machine must have their cutting edges prepared and ground to a different clearance (or bevel) than the cutters of a machine for slitting paper, and upon the attention paid to this seemingly small detail largely rests the accuracy and smoothness with which the film strips will be cut. Another item of importance is the temperature and humidity of the dark-room in which the film is slit, which must be so regulated as to minimize, as far as possible, the generation of static electricity by the frictional contact of the rotary cutters with the celluloid film. As will be readily apparent, considerable havoc would be wrought if any appreciable amount of sparking (due to static electrical discharges) occurred while the film was passing between the cutting wheels. Static troubles, incident to the slitting operation, are avoided by regulating the speed at which the coated celluloid sheet passes through the slitting machine, as well as by maintaining the darkrooms at a carefully regulated temperature and degree of humidity. Under favorable atmospheric conditions the film roll can be slit into ribbons at the rate of 25 feet per minute and if suitable precautions are taken a higher speed might be possible. As is generally known, the standard width for a cinematograph film strip is 35 mm., and when it is borne in mind that this strip must be capable of passing readily through the mechanisms of any and all of the numerous makes and models of cameras, projectors, and printing machines on the market it will be appreciated that cinematographic film strips must be cut with great accuracy from the parent roll of stock, otherwise troubles of considerable magnitude will ensue when the film strips are issued for use. Obviously, if there is any inaccuracy in the width of the film band it should be discovered before it leaves the manufactory, so all reputable makers of cinematograph film stock run the bands through a verifying machine as soon as they are received from the slitting room. Such a device is known as a " width testing machine " and is similar in appearance to that shown in Fig. 4. As will be appreciated after an inspection of Fig. 4, the width of the film is verified while the roll is being rewound on the device there illustrated. In Fig. 4, A is a support to which the roll of cine film is mounted by the removable spindle at its center. The end of the film strip to be tested is next passed through the device B and from thence to the rewind spindle E. The device B is so constructed that it touches the film strip only at its edges, and is so adjusted that it can detect a variation as slight as 1/2000 inch in the width of the film band. Attached to the width testing device B (Fig. 4) is a pointer C which plays over the face of an indicator dial D. When a film strip is being tested (as to its accuracy of width) the operator rewinds the film from A to E (Fig. 4) and watches the indicator dial D. The slightest variation in the width of the film from the 35 mm. standard would cause the rejection of the roll of film being examined.