8mm Forum: Sproketless Projectors

This is topic Sproketless Projectors in forum 8mm Forum at 8mm Forum.

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Posted by Paul Adsett (Member # 25) on May 01, 2019, 11:20 AM:

The only sprocketless projector I have is the Eumig 926GL Stereo. Actually it does have a rear sprocket, but the all important feed sprocket, which isolates the feed spool tug, is absent, being replaced by a tiny flapper roller on a thin metal beam spring [Roll Eyes]

. This works fine with a rock steady picture up until the last few minutes of any reel, when the claw is tugging the supply film reel close to the center hub of the reel and the jerking force on the reel is much higher. This produces film unsteadiness and sometimes 'free running' of the film over that last couple of minutes. I have tried increasing the gate clamping force by stretching the gate springs a little, and that helps a bit but does not totally solve the problem, the root cause of which is the lack of a feed sprocket.
So my questions are this, are all sprocketless projectors subject to this problem of unsteady pictures at the end of the reels? And what are the advantages (if any) of no feed sprocket?

Posted by Nick Vermeirsch (Member # 4136) on May 01, 2019, 12:15 PM:

Hello Paul. I had the exact same problem with my Silma Delta projectors: a steady image, just the last minutes give trouble and jumping images, i really see the projector jerking the film into the machine, which of course are the reason for this problem, as you also describe. I may not say that all my projectors which lack these sprockets have given problems. My first projector was a Silma S222, also without these sprockets, and this one never gave me problems.

Posted by Dominique De Bast (Member # 3798) on May 01, 2019, 12:18 PM:

Those kind of projectors are not recommended to be used with Long Play Units.

Posted by Maurice Leakey (Member # 916) on May 01, 2019, 01:33 PM:

Paul
You recently said you had modified the feed on your Eumig 926.
http://8mmforum.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=012872

Posted by Tom Photiou (Member # 130) on May 01, 2019, 01:34 PM:

Do these rely on the claw pulling the film through? I wouldn't have thought that was good for the film, maybe im wrong?

Posted by Paul Adsett (Member # 25) on May 01, 2019, 01:52 PM:

On the Eumig 900 to 929 series none have a top sprocket and the claw has to take the force required to pull the film off the supply spool. This is probably the case for all other sprocketless machines as well.

Posted by Maurice Leakey (Member # 916) on May 01, 2019, 01:53 PM:

Tom
The answer is yes.
As Paul says, quite a few Super 8 projectors have this system of the claw pulling in the film from the feed spool.

Posted by Paul Adsett (Member # 25) on May 01, 2019, 05:37 PM:

Maurice, the two rollers that I installed on the top of the S926GL are very helpful in dampening the wild thrashing mode of the film coming off the supply reel, but unfortunately this still does not isolate the film tension load from the claw, so the film still tends to jump or skate through the gate towards the end of the reel.
And that's the bad thing about sproketless projector design- the behavior of the film is dependent on so many variables, spool hub diameter, friction coefficient of the film and gate, spring loading of the gate, flexibility of the film base etc. So some reels will run fine with no problems and others will be very unhappy towards the end of the reel.
All of which raises the question why would anybody(particularly 'The Wizard's of Vienna') design a sproketless projector in the first place?

Posted by Nantawat Kittiwarakul (Member # 6050) on May 01, 2019, 08:20 PM:

Some Fujicascope sprocketless projector does have sort of rubber FEED WHEEL to help pulling the film off the reel,which I found to work impressively well. Never have problem pulling film off the supply reel ever with that. [Wink]

Posted by Paul Adsett (Member # 25) on May 01, 2019, 09:26 PM:

I think that would work fine as long as it is powered, like a sprocket, to deliver film to the claw at the correct rate.

Posted by Maurice Leakey (Member # 916) on May 02, 2019, 10:14 AM:

The main problem of the Eumig 926GL is its design with the two spools in a concentric formation. This is OK for the take-up, but the feed spool's position means that the film has a somewhat abrupt 90 degrees turn to get into the gate.
In my Agfa Sonector LS2 (also claw pulled) the film comes down from the feed spool in an almost vertical position to get to the gate, it's not ideal but does seem to work OK.

Posted by Maurizio Di Cintio (Member # 144) on May 02, 2019, 04:02 PM:

To answer Paul's question, which I have been turning in my mind for a long time as well, the possible solution I came up with is quite simple... Economy: fitting the upper sprocket requires machining or mould printing the sprocket and the cog/wormgear which will later make it rotate. That's at least three more parts plus miscellaneous bits and bops (am I right?) such as springs, washers circlips etc. When Eumig designed this assembly they probably had in mind the number of units they sold of the projectors from the previous Series 800 which had sold in hundreds of thousands (I recall model 810 alone sold over 200.000 units). This never was the case for any of the later series models. So the scale economy they were presumably expecting based on those numbers, was never achieved; in fact the reverted to a regular two reel-arms plus two sprocket wheels right after the end of Model 926's production: model 932 and subsequent ones have all more traditional designs with the 800' spool upgrade. Other than that I cannot see any real advantage with a single sprocket film drive over a two sprocket system, except - maybe - for esthetic reasons: this may be debatable but IMHO indeed all the former Series 900 projectors have a point of distinction under this respect and certainly they stood out in any high street shop windows as opposed to their competitors' products... Just my toppence...

Posted by Paul Adsett (Member # 25) on May 02, 2019, 05:34 PM:

To Maurice's point: yes the film coming off the supply spool of the 926 is essentially reversed in direction (180 degrees) when entering the feed slot at the top of the projector. In addition to that the film also has to be displaced sideways because of that coaxial reel arrangement. This is all accomplished before the film enters the gate by a molded plastic piece with 3 tiny rollers and a flapping roller on a metal beam spring, to help absorb the tug of the film on the claw. Its all a very complex and tortuous film path and a real nightmare for the film, although in all fairness, as bad as this design is, amazingly I have never scratched any film on my 926. So Eumig did a great job on a rotten design concept! [Big Grin]

But all this complexity just to make a projector look novel and different from the competition was a very bad decision indeed. I am sure there were engineers at Eumig ( particularly those who had designed the prior superb 800 series projectors) who hated this coaxial single sprocket design, and surely knew of its peculiarities and fussy operation, but were in all likelihood overruled by the demands of the marketeer's and bean counters.

Posted by Shane C. Collins (Member # 5641) on May 02, 2019, 07:44 PM:

The Sankyo 2000H projector I have is sprocketless. It uses a rubber feed roller, that I assume, helps with applying the proper tension to the film. I've never experienced issues with the film jumping at the end of the reel.

Posted by Paul Adsett (Member # 25) on May 02, 2019, 08:21 PM:

That's useful information Shane. Do you know if that roller is spring loaded in any way? Can you post a photo?

Posted by Nantawat Kittiwarakul (Member # 6050) on May 03, 2019, 01:16 AM:

Shane's Sankyo is probably the same design as my Fujicascope. [Wink]

So I know how it works out.

Nope,there's no spring-loaded design there. The film is just loosely wrapped around that feed wheel which is a bit over-spinning,to assure that the film will not be directly "pulled" from the feed reel by the claw in any way. But since the film is not in solid contact with the wheel,the film will simply "slip" before the upper loop size goes too big. The upper loop former helps keeping the upper loop in proper size too.

Ah,I should have uploaded the video of my projector when running. Would be much easier than this lengthy explanation. [Embarrassed]

Posted by Maurice Leakey (Member # 916) on May 03, 2019, 02:36 AM:

The Sankyo 2000H is a dual gauge model which uses rubber rollers in place of conventual sprockets, this avoids a change of sprockets for each gauge.
https://www.filmkorn.org/super8data/database/projectors_list/projectors_sa nkyo/projectors_sankyo.htm

Posted by Brian Fretwell (Member # 4302) on May 03, 2019, 02:48 AM:

The Eumig 510D and 610D (possibly the P8 Dual too) silent projectors had a completely sprocket-less film path but both had conventional front feed spools. I haven't used one recently but think they also suffered from unsteadiness on the last few feet, especially with a small centered spool.

Posted by Shane C. Collins (Member # 5641) on May 04, 2019, 08:20 PM:

I mainly use the Sankyo 2000H to preview movies that come back from the processing lab. Even with a small 50 ft reel there is no jumping or unsteadiness. My impression is the rubber feed wheel has something to do with this.

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