Film-Tech Forum ARCHIVE: Threading up Simplex 35s - Proper Frameline Position on Holdback Sprocket

my profile | my password | search | faq & rules | forum home

»	Film-Tech Forum ARCHIVE » Operations » Film Handlers' Forum » Threading up Simplex 35s - Proper Frameline Position on Holdback Sprocket (Page 2)

This topic comprises 2 pages: 1 2

Author

Topic: Threading up Simplex 35s - Proper Frameline Position on Holdback Sprocket

Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

posted 11-02-2007 01:33 PM

Hmmmm.....stuff does pass from one generation to the next, but one never knows exactly if it is true or just the older generation's misinformation.

When I was being shown how to thread -- YEARS ago, I might add --I actually asked the old timer who, like many at the time, called it a "holdback" sprocket and like Michael, I asked why it is called the "holdback" sprocket. He told me because it dampens or "holds back" any irregularlities/vibrations/torque from the takeup reel from transfering back into the soundhead. If it and the small film loop it forms between it and the first sprocket drive weren't there, those takeup reel vibrations would be impacted on the film at the cell and heard on the soundtrack.

Fact or fiction? I have no idea. I haven't ever heard anyone else explain that as the reason or if it actually functions that way, but and have never had any reason to question it....until now. It sounds passably logical, but that doesn't make it so or that the old timer was right or just pulling it out of his ass. Alas, now I am the old timer. Do I pass this on or not?

| IP: Logged

Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 11-02-2007 04:25 PM

Actually,

The "holdback" sprocket is the last sprocket in any film projector/soundead. It does what its name implies...it holds the film back from the force of that which is pulling the film. That is true wether it be a take up reel trying to pull the film faster than the projector is allowing it to come out or a platter trying to do the same thing. The first sprocket is the feed sprocket because it is feeding the projector. It is all rather simple really and those names have been in use a long long time. I'll have to look at some of our old silent-era manuals and see if they use the holdback term on the last sprocket in the projector...particularly on the ones that had reels. Those that had "bags" may not have used the holdback term...since they were not holding anything back.

Note too, the pitch on the holdback sprocket was traditionally shorter to deal with the tension better...or so the idea goes. You can find that the original part numbers for Century, Norelco and I believe Simplex were different for the Holdback sprocket versus a feed sprocket. What I do know from experience is that on a Norelco, even a new holdback sprocket with an "H" on its face was more likely to "sing" than a feed sprocket when used in the holdback position so I'm not to sure on the facts backing up the theory. As most know, LaVezzi and other suppliers now only have the one type of sprocket (feed) for both positions on Century projectors and likewise for Norelco projectors....so it wasn't such a good idea that it has continued. It also never existed in the VKF variety of sprockets.

Steve

| IP: Logged

Robert E. Allen
Phenomenal Film Handler

Posts: 1078
From: Checotah, Oklahoma
Registered: Jul 2002

posted 11-02-2007 10:43 PM

You're absolutely right Steve. I started as a projectionist in 1950 and that was the name and stated purpose of the hold-back sprocket. The feed sprocket was also called the pull-down sprocket.

| IP: Logged

Monte L Fullmer
Film God

Posts: 8367
From: Nampa, Idaho, USA
Registered: Nov 2004

posted 11-03-2007 02:03 AM

..then you have Christie's "upper constant speed, middle constant speed", and "lower constant speed" sprocket terms.. being the belt driven assemblies in an all-in-one frame..

| IP: Logged

Louis Bornwasser
Film God

Posts: 4441
From: prospect ky usa
Registered: Mar 2005

posted 11-03-2007 07:54 AM

....and given the wow/flutter..."constant speed" is only just a name on the Christie. Louis

| IP: Logged

Robert E. Allen
Phenomenal Film Handler

Posts: 1078
From: Checotah, Oklahoma
Registered: Jul 2002

posted 11-03-2007 09:15 AM

Hey Louis!

The last house I worked (a CineMark 15 screener) our booth tech put rubber bands around the sound drum rollers to stop the wow and flutter. He said the company wouldn't put out the $2,000 per machine to correct the problem. But the rubber bands worked. He said the problem was caused by the fact the rollers worked against each other. Can you believe it? A modern 15 screen multiplex and the sound is assisted by rubber bands?

| IP: Logged

Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 11-04-2007 09:16 AM

quote: Robert E. Allen
Can you believe it? A modern 15 screen multiplex and the sound is assisted by rubber bands?

Kinoton and Ernemann both do the same thing... rubber bands on the sound drum!

quote: Steve Guttag
Note too, the pitch on the holdback sprocket was traditionally shorter to deal with the tension better...or so the idea goes. You can find that the original part numbers for Century, Norelco and I believe Simplex were different for the Holdback sprocket versus a feed sprocket. What I do know from experience is that on a Norelco, even a new holdback sprocket with an "H" on its face was more likely to "sing" than a feed sprocket when used in the holdback position so I'm not to sure on the facts backing up the theory. As most know, LaVezzi and other suppliers now only have the one type of sprocket (feed) for both positions on Century projectors and likewise for Norelco projectors....so it wasn't such a good idea that it has continued. It also never existed in the VKF variety of sprockets.

Thats because the VKF sprocket inherently generates LESS sprocket tooth ripple on its own. So holdback sprockets are not required. The rounded teth do make a huge difference. When we had the VKF's produced ffor the DP-70 we asked about having seperate holdback versions made up and their reply was that "it didn't matter any more, the VKF tooth design negates the need".

Mark

| IP: Logged

Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 11-04-2007 03:50 PM

Well, in all fairness, the Kinoton and Ernemann both use a loose-loop type soundhead. The use of O-rings allow one to decrease the amount of pressure the pinch roller must apply to prevent slippage. Kinoton, for the longest time did not use O-rings and I find it a welcomed change. One was often needing to increase pinch roller tension to the point that the film almost wanted to slip out in order to have flutter free sound at changeover. In fact, that is how I set the tension...not by any tensino gauge but by when the flutter was gone...it had to be gone in less than 7-seconds. With the O-rings, the tension dramatically reduced. Kinoton has also augmented their later soundheads with a damped roller too to minimize flutter.

Steve

| IP: Logged

Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 11-05-2007 08:02 AM

I think its easier to filter a loose loop sound reproducer than one with a tight loop for sure. The rubber "O" rings are fine till they wear or crack... a cheap replacement too. I'm surprised that Kinoton and Phillips before them didn't always have the extra damper in there as the FP-5 version of the Phillips sound head had the damper roller and its much lower in wow than all the others without it... FP7 and up.

Mark

| IP: Logged

All times are Central (GMT -6:00)

This topic comprises 2 pages: 1 2

Printer-friendly view of this topic

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.