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Mechanical vs. Electronic Frictions - A differentiation should be given between traditional mechanical friction clutches and electronically controlled friction drives that can respond to reel mass and compensate accordingly. Kinoton's electronically controlled frictions are designed operate with cores as small as 2". The mass and hub size issues that make split reels ill-advised for mechanical frictions are less of a concern with electronically controlled frictions. The circumstances under which split reels may be used for projection should be added, along with the caveats necessary when using split reels (the flange attached to the hub should be placed on the inboard side of the spindle, a 3" or ideally 4" core should be used, the outboard flange may may need to be wound back slightly to prevent kissing, etc.).
Hub-to-flange ratio - In order to maintain appropriate tension over the course of a reel, the ratio between the diameter of the flange and hub should be no more than 3:1. For large reels where this ratio cannot be achieved, the use of a floating hub can help mitigate the issue because the weight of the flanges is less of a factor on the starting torque.
Reel Size Calculation The roll diameter can be calculated from the following equation:
D = Square root [ ( (48 x L x t) / Pi) + (C x C) ]
D is roll diameter in inches
L is length of film roll in feet
t is film thickness in inches
C is core/hub diameter in inches
Thickness - Triacetate base by itself has a thickness of about 0.0056", polyester base has a thickness of about 0.0043", and emulsion thickness will vary. Kodak 2383 on polyester has a total thickness of about 0.0053).