Film-Tech Forum ARCHIVE: 24" reel holds how many ft. of film?

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Posted by Don E. Nelson (Member # 1049) on 07-18-2003, 10:30 AM:

How many feet of 35mm film fit on a 24" reel? And what is the largest reel made for a vertically mounted pedestall projector?

Posted by Gordon McLeod (Member # 33) on 07-18-2003, 11:36 AM:

4000' feet of acetate on a 5" core and about 5800 feet of estar
The largest on board reel was the cinemecanica with 36" reels on vic8's

Posted by Stephen Furley (Member # 1277) on 07-18-2003, 11:37 AM:

It depends on the size if the core, the thickness of the stock and, rarely now, whether the print is mag striped.

For triacetate stock, without stripe, on a five inch or thereabouts core, you should get about 5000 feet. Somewhat more with polyester, and somewhat less on a spool with the larger size core.

It also depends on how far you are prepared to fill it, I've seen film wound about four inches beyond the flanges. [Eek!]

The largest spools I've used, on towers, are about 37 inches, with a core about ten inches, and hold about 1200 feet of triacetate, or closer to 1500 feet of polyester.

There is a Fedi projector at Bletchley Park Museum which takes large spools on the base of the machine itself. I think they are somewhat larger, maybe 40 inch or so.

Posted by John Pytlak (Member # 331) on 07-18-2003, 11:59 AM:

The roll diameter can be calculated from the following equation:

D = Squareroot [ ( (48 x L x t) / Pi) + (C x C) ]

Where:
D is roll diameter in inches
L is length of film roll in feet
t is film thickness in inches (about 0.0053 for Kodak VISION Color Print film)
C is core/hub diameter in inches

For example, for a shipping reel with a 4-inch core, and a film thickness of 0.0053 inches, 2000 feet of film will have the following diameter:

D = Squareroot [ ( (48 x 2000 x 0.0053) / Pi) + (4 x 4) ]

= 13.3 inches

Posted by Ken Lackner (Member # 1002) on 07-18-2003, 12:56 PM:

If something seemingly insignificant as film thinckness makes a difference when calculating the diameter, then wouldn't the diameter also depend on how loosly or tightly the film is wound?

Posted by Bill Gabel (Member # 1105) on 07-18-2003, 01:15 PM:

Our two Cinemecanica Vic 8's in the GCC AVCO Theatre main house (Westwood, Ca.) could handle 12,000 reels and were auto change-over.

They cut the house into two a few years ago. [thumbsdown]

Posted by Evans A Criswell (Member # 381) on 07-18-2003, 01:18 PM:

How tight the film is wound could be modeled in the formula by slightly changing the value for film thickness. You have to remember that the formula gives you a value, but the real life value could be slightly different.

Posted by John Pytlak (Member # 331) on 07-18-2003, 01:19 PM:

quote:
If something seemingly insignificant as film thinckness makes a difference when calculating the diameter, then wouldn't the diameter also depend on how loosly or tightly the film is wound?

Yes, a very loosely wound roll will be larger, but you should not wind it too loose anyway. SMPTE Recommended Practice RP106 specifies a tension of 6 to 16 ounces (1.7 to 4.4 Newtons) for 35mm films.

Posted by Stephen Furley (Member # 1277) on 07-18-2003, 01:37 PM:

Gordon wrote:

quote:

4000' feet of acetate on a 5" core and about 5800 feet of estar
The largest on board reel was the cinemecanica with 36" reels on vic8's

Gordon, spools of the same nominal size or capacity can vary considerably, nominally 24 inch ones were often listed as being nominally 6000 feet, in the days when triacetate prints were the norm. In my experience this is over optimistic, but your figure of 4000 feet seems rather conservative. Running two 2000 foot rolls on a 24 inch spool was quite common at one time, partly because the spools would have been over full if a third part was added, and partly because many lamps would not burn for long enough on a single trim of carbons. Such a spool would be far from full, though if a third part would not fit, then 4000 feet was the practical limit, unless you added a few adverts or trailers on the beginning if the first spool, or had a short part somewhere in the print.

Or is print stock over there somewhat thicher than it is here?

Ken wrote:

quote:

If something seemingly insignificant as film thinckness makes a difference when calculating the diameter, then wouldn't the diameter also depend on how loosly or tightly the film is wound?

Film may be only a few thou thick, with dhe difference between triacetate being only a fraction of that, but there are many thousands of layers of film on a full spool, and it all adds up. The difference in thickness, as a percentage, is significant.

A slack wind would increase the size of the roll, but incorrect tension, either too high or too low, is likely to cause damage to the film, and within the small range of tension which might be considered 'correct' the difference in the size of the roll would also be small.

Posted by Gordon McLeod (Member # 33) on 07-18-2003, 01:41 PM:

The nominal norm was 2 full reels almost filled on 24" reel with a 5" core
The 25" reel was the standard 5000' 3d reel
26" was the norm for 6000'

Posted by Brad Miller (Member # 2) on 07-18-2003, 04:11 PM:

Am I going to have to take a frame counter to this??? A 24 inch reel will hold a LOT more film than 4000 feet, even of acetate.

Posted by Gordon McLeod (Member # 33) on 07-18-2003, 04:27 PM:

You may be right since off the top of my head I was thinking of mag fullcoat and a 24" reel full to the edge here is 52min of estar mag stock
But I would have assumed that mag estar stock would be about the same thickness as acetate print stock

Posted by Scott Norwood (Member # 30) on 07-18-2003, 08:45 PM:

My favorite configuration is 26" reels with 7" floating hubs. These will each hold the equivalent of four not-quite-full shipping reels' worth of ESTAR-base film. Most features will fit onto two 26" reels, while many would require three of the 24" reels (example: "LA Confidential" is eight reels long, but fits on two 26" reels with room to spare). The 26" reels also fit nicely onto standard Kelmar reel arms (the only enclosed reel magazines that I've dealt with only have 2000' capacity).

Posted by Steve Kraus (Member # 476) on 07-19-2003, 11:00 AM:

Ken asked:
If something seemingly insignificant as film thinckness makes a difference when calculating the diameter, then wouldn't the diameter also depend on how loosly or tightly the film is wound?

Seemingly insigificant? Perhaps you want to rethink that as I do believe I can fit more turns of hair-thin audio tape onto a reel than inch thick garden hose!

But the second part of your comment is correct, the wind tension will matter although how much I'm not sure. But I would suggest that the thickness be derived empirically (that means from real world experimentation) than from some official figure. Like take a reel wound at whatever tension you have in mind, mark two points on the edge of the pack a certain distance apart, and then unwind counting how many turns of film were in that distance. Divide and there is your real world thickness value.

Back when I was in college I spent some time pondering the question of reel diameters and footage and came up with some formula based on an average turn or some such while my roommate the Nuke E. did something with limits and the end result was the same. Much later I realized that the whole thing could be considered as a measure of areas. Areas as viewed from the side of the reel. The area of a circle is pi * radius squared so the area of the film pack would be the area of the outer radius minus the area of the inner radius. The film itself can be viewed as a rectangle whose area is length times width, width being the thickness since we're talking about film viewed on edge. So divide the area of the film pack by the tiny edge thickness of the film and you get the length. I believe crunching these formulae will result in the same as John's.

Posted by Ken Lackner (Member # 1002) on 07-19-2003, 01:19 PM:

Okay, people. I know that the thickness isn't insignificant. Poor choice of words. I just meant that if you hold a piece of accetate next to a piece of polyester, you can't tell the difference because it's so small. The difference becomes apparent when you wind them on to spools, however. That's why I said "seemingly insignificant." The difference may seem insignificant at first, but it adds up.

Posted by Steve Guttag (Member # 268) on 07-20-2003, 02:53 PM:

This may stike some of you as odd but reels are listed in their unfinished sizes like wood (ever measured a 2 x 4?). A 24 inch reel is slightly less than 24 inches in diameter.

My personal favorite "6000-foot" reel is the 25" x 7" hub. It rarely if ever has take up issues and will fill all MUTs and rewinders I've tried. 26" reels can not make that claim.

Steve

Posted by Brian Guckian (Member # 1678) on 07-20-2003, 06:19 PM:

Cinemeccanica's 6000ft reels (24.25ins dia. with a 5.75ins dia. hub) appear to have a safe operating capacity of approx. 6400ft for polyester film, and a maximum capacity of approx. 6500ft (to the start of the bevelled rim).

BTW are these easily obtainable in the States?

Posted by Don E. Nelson (Member # 1049) on 07-21-2003, 02:53 PM:

Brian, I get mine on E-Bay occasionally.