Film-Tech Forum ARCHIVE: Film loosing tension around sound drum

This is topic Film loosing tension around sound drum in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=007779

Posted by Ian Bailey (Member # 1752) on 01-27-2006, 01:47 AM:

Hi
This problem is happening on a Monee(all in one projector).
I'll wait 5 minutes for you all to stop laughing!!!!
Thread the machine up and start the show and at some stage the tension on the sound drum is lost.The amount of film between the intermittent and the bottom sprocket in the sound head appears to increase.Sometimes it doesn't get any worse and the sound is still ok but it has got to the point where the analogue sound was affected so had to stop the show and reset the tension.
This was only happening on one print but now has happened on another one.
I have had a bit of trouble with the bottom sprocket and layover.With the layover adjusted to 2 thicknesses of print, when you were threading up,the film could pull back off the sprocket as if the layover wasn't holding the film against the sprocket.So I adjusted the layover a bit closer.
The film travels half way round the sprocket on it's way out of the projector so I can't see that the sprocket and layback is part of my problem.
Help!!
Ian

Posted by Monte L Fullmer (Member # 2797) on 01-27-2006, 02:07 AM:

Hi Ian..

..got a bad gear on the middle constant speed sprocket assembly, which is after the intermittent assembly on the back side? Sounds like a gear tooth is beginning to hop from the vertical shaft causing you to loose that tension. Or, it could be the lower assembly's gear doing the same as well. Also,the nylon or fibre on the gears could be getting tired and worn itself.

Also, how are the bearings on the vertical shaft itself? If the bearing are getting weak the vertical shaft could begin to wobble out of round and not turn true vertical, and with this wobble, the vertical gears may be missing the sprocket's gears and causing the mesh not to be constant. Are the bearing brackets tight against the frame casting as well so the shaft is vertical and not at an incline?

Also, are the two assemblies tight against the frame casting? I've seen the assemblies get loose somehow and the teeth aren't meshing against the vertical shaft too well and this could also cause loop loss.

Good luck on this. thx-Monte

Posted by Mark Gulbrandsen (Member # 72) on 01-27-2006, 08:19 AM:

Its most likely a sound head to projector drive belt thats too loose. If they are too loose the soundhead sprocket will start turning just before the bottom projector sprocket does and may cause the filmto slop like you are seeing. Or you may have a bad belt idler. Is the pad roller worn? Is the sprocket a VKF?

Mark

Posted by Richard Fowler (Member # 893) on 01-27-2006, 08:45 AM:

Mark,
it is a one piece Monee...more like a direct drive Century.

Posted by John Eickhof (Member # 323) on 01-27-2006, 09:49 AM:

sounds like pad roller adjustment or damage on film.....adjust pad roller clearance from sprocket at 2 thicknesses of film. Also check steel roller below lower sprocket and see if it has not frozen up and is still turning, if it stops the film can slack against the sprocket and tension will be lost in the sound head.

Posted by Louis Bornwasser (Member # 3063) on 01-27-2006, 11:15 AM:

Remove old sound sprocket; install junk sprocket. Turn junker sprocket with pliers and you will find that it moves in relation to the lower feed sprocket in the projector. You will know what to do.

If this were "a standard drive" on a Century for example; the only spot that is not KEYED is the lower belt sprocket on the projector drive. Very common.

If on a "direct drive;" you will just have to observe where the "slippage" is. Louis

Posted by Monte L Fullmer (Member # 2797) on 01-27-2006, 12:53 PM:

..like a sloppy coupler between the two heads?

Posted by Pete Naples (Member # 761) on 01-27-2006, 04:44 PM:

Tha pad rollers on Monees LOVE to wear in odd ways, couple that to sprockets made from paper mache, and slippage over the sprockets is common. Quite possibly replacing hte lower hold-back sprocket and it's pad roller will sort it. (Don't replace with monee, replace with Century or equivalent)

Posted by Ian Bailey (Member # 1752) on 01-29-2006, 06:01 PM:

Thanks guys
Sorry it's taken so long to reply.
Monte-the possible causes you have stated for this problem are the same as what a local repairer felt could be the problem.If it is worn gears below the intermittent do you think that I should just replace these gears or the whole shaft complete.
I am having a problem with the bottom sprocket and pad roller,as Pete said the pad rollers wear in odd ways and this one is definitely worn to the point that it is difficult to adjust properly.As the film wraps half way round this roller on it's way out of the projector I just can't see how the film could jump back off the sprocket as the projector is running unless the layback arm and pad roller are being affected by a splice passing through causing the layback arm to open a bit momentarily.
Louis,I'm absolutely confused with your explanation could you give me a bit more information as to what you mean-sorry for being a dummy!!!
Ian

Posted by Monte L Fullmer (Member # 2797) on 01-29-2006, 06:22 PM:

Basically, what Louis is giving you is that the lower sprocket is actually in a separate drive than the upper assembly. Put on that old sprocket on that middle shaft, crank it around with a pair of pliers, and see if the upper mechanism turns exactly with the lower sprocket.

Put a mark at 12 o'clock on the middle and the lower sprocket. Crank that middle sprocket and see if the two marks rotate exactly the same and return to the same point when you stop.

Or, see when you crank that middle sprocket if the bottom sprocket moves exactly with it, or is there some delayed rotation of that bottom sprocket - or even any jumping is noticed.

-Monte

Posted by Ian Bailey (Member # 1752) on 01-30-2006, 06:59 AM:

Thanks Monte- now I understand.
Ian

Posted by Jean-Pierre Van Hoof (Member # 2063) on 01-30-2006, 02:08 PM:

Hi Ian,

Had a similar problem on a Phillips cp20.
It came out that for some kinda weird reason the last sprocket,
that is made up of two halfs, was misaligned for just a few mm.
That made the film jump between the two sprocket halfs and decrease the loop after a while.

<S>

Posted by Monte L Fullmer (Member # 2797) on 01-31-2006, 02:17 AM:

quote: Ian Bailey
If it is worn gears below the intermittent do you think that I should just replace these gears or the whole shaft complete.

..I'd do just the gears if the shaft bearings isn't showing any excessive wear, noise and wobble. Your call on this one if you want to replace complete.