Film-Tech Forum ARCHIVE: Bumping reel

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Posted by Demetris Thoupis (Member # 833) on 11-14-2002, 02:04 PM:

Hi again,
One of my V 5 can take huge reels which can fit a whole feature on. The problem I have is that when the reel becomes a bit loader (half or a bit more) then after it completes a circle in bumps and the machine shakes and therefore the picture shakes. Any ideas what I can do?

Posted by John Pytlak (Member # 331) on 11-14-2002, 02:16 PM:

Tension control with large reels can be problematic. If the feed reel has just a friction brake to provide holdback tension, try increasing the tension. The "reel" solution is a torque motor holdback that maintains constant film tension as the roll diameter changes from a full reel to near the hub.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
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Posted by Daryl C. W. O'Shea (Member # 1303) on 11-14-2002, 02:17 PM:

Do you mean that the reel's inner flange hits the arm? Does it do this on all reels or just some warped ones? If only one side of a reel is warped enough to cause a problem (and isn't too bad to cause winding problems) try turning it around.

Edit: John, beat me. If it's a bounce, lightly drag your finger on the reel flange. If the bounce goes away you'll know that it is the clutch tension. Watch out, if the bounce gets 'too large' it could pull the top loop out. Not as much a problem with the V5's large sprockets, but it could still happen.

Posted by Joe Beres (Member # 678) on 11-14-2002, 04:23 PM:

I would guess that John and Daryl are on the right track, but there might be (at least) one other possibility. How are you loading the film onto the large reels? It sounds like a potential problem is that the film is not tightly wound onto the reel. Is this a possibility? If that is the case, the loose film can drape a bit on the hub and then cause the reel to spin unevenly. This can also cause some severe tension or cinch scratches on the print. Make sure that the film on the feed reel is wound evenly and and tightly as weel as following the instructions that John P. and Daryl provided. Hopefully some of the advice will help. Good luck.

Posted by Gordon McLeod (Member # 33) on 11-14-2002, 05:44 PM:

The clutch on your upper arm may have the felt pad dry. It is important that you take that clutch appart periodicaly and soak it in the clutch oil that Cinmecanica provides (if none is available a very heavy oil should do
Adjut the tension so it keeps it from just overshooting as if you have too much it will strain the perfs when it gets to the centre hub and the reel is spinning fastest

Posted by Kenneth Wuepper (Member # 1174) on 11-14-2002, 09:46 PM:

I recall that RCA made a "fluid Clutch" for their 1600 series 16mm projector takeups. This was a clear plastic housing with fins inside and contained Silicon fluid.

The clutches worked very well and the takeup tension was proportional to the speed of the spindle. Too bad there is not a version of this available for the payout spindles.

KEN

Posted by John Pytlak (Member # 331) on 11-14-2002, 09:53 PM:

Ken: I'm not familiar with the takeup clutch you mention, but it would seem that a holdback spindle that used a turbine in a viscous fluid to provide drag would be an excellent idea! A principle kind of like the "Air Dyne" excercise bikes:
here

Posted by Kenneth Wuepper (Member # 1174) on 11-15-2002, 06:55 AM:

John,

The way that the "fluid clutch" worked was uncanny. When the reel and shaft turned at nearly the same speed, the clutch was almost locked but as the film takeup reel filled, it became active and applied the right tension for the takeup.

We had little trouble with the ones I serviced (about 150). The only one I ever replaced had a cracked case and the 'fluid' leaked out. In cleaning it up we found out it was a Silicone substance.

In a payout situation, the tension would be greatest when the reel is turning slowly and then decrease as the speed of the rotation increased near the center of the reel. Seems like the ideal mechanism to me.

When running 6,000 foot reels on the Zeis Favorite 16B, it is necessary to adjust the tension of the payout once during each showing to minimize sprocket tension during the second half of the show.

KEN

Posted by Demetris Thoupis (Member # 833) on 11-15-2002, 07:12 AM:

Sorry,
Should have mentioned it before.
We are not talking about the upper arm reel but the bottom one. The one which the "played" film is put on. It does it with all the reels which I have.
Demetris

Posted by Scott Norwood (Member # 30) on 11-15-2002, 08:22 AM:

The Concept 2 rowing ergometer ( here ) uses the air resistance principle, too. Supposedly, it is the closest possible simulation of actual water resistance without using real water.

Posted by Kenneth Wuepper (Member # 1174) on 11-15-2002, 01:11 PM:

Demetris,

This sounds like a classic case of bad or broken bearings. The shaft is undoubtedly supported in bearings and if they are ball bearings which are worn they can run loose in the race and make this thumping effect. I would think that the bearings are of the roller type to carry the heavy load and these can also become worn and cause the shaft to move off its axis.

KEN

Posted by Daryl C. W. O'Shea (Member # 1303) on 11-15-2002, 03:50 PM:

If it 'bumps' exactly once per rotation I would expect a bent shaft.

Posted by Gordon McLeod (Member # 33) on 11-15-2002, 04:59 PM:

Ken said"When running 6,000 foot reels on the Zeis Favorite 16B, it is necessary to adjust the tension of the payout once during each showing to minimize sprocket tension during the second half of the show."
Never had that problem and we have a lot of 16Bs up here. If that is the case I would tend to believe the felt in the clutch is dry or the plates are worn

The 1/2" spindles on most of the Vic5's drive the reel by a dog that goes into one of four holes . Often the pin will get a grove in it and as the reel passes dead centre it will jump ahead making a clunk

Posted by Demetris Thoupis (Member # 833) on 11-16-2002, 04:31 AM:

Yes Gordon. That is exactly what it does. Now. Is there something that can be done for it? Or am I in the mercy of the painful shaking picture?

Posted by Gordon McLeod (Member # 33) on 11-17-2002, 03:39 PM:

Replace the shaft if it is worn also check th hole is the reels that they arn't egg shaped