Film-Tech Forum ARCHIVE: Film start trips fail-safe

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Posted by Dan Chilton (Member # 2288) on 07-21-2007, 08:17 PM:

We run reel-to-reel, and lately when I start the projector, the take-up reel spins so that the film in the fail-safe slacks up and kills the motor. I've gotten to the point where I just hold my finger on the power switch until I know it's going to run without dying.

What do I need to do to remedy this? Do I need to tighten or loosen the spring on the back of the reel arm? Shorten the belt that runs the take-up reel? Any suggestions would be great.

Posted by Monte L Fullmer (Member # 2797) on 07-21-2007, 08:45 PM:

Sounds like it - the tension needs to be adjusted tighter somewhat on that takeup shaft. Dhes the reel 'bounce' around when it begins to spin?

Also, if you can disassemble that clutch assembly, see if the cloth friction pad had enough oil on it, otherwise a dry pad could cause the irratic takeup when the reel begins to turn.

Are your running 6k reels? If so, the tension really has to be up there, but not so tight that the film is 'singing' across the last holdback sprocket even when the takeup reel is full.

And if it's 'singing', even with low tension, I bet that the sprocket either needs to be turned around, or replaced due to the film creating small cavities at the base of each tooth on that sprocket and this condition is called "a hooking sprocket".

Posted by Dan Chilton (Member # 2288) on 07-21-2007, 08:54 PM:

We're running 6k reels. No singing, but the take-up reel does bounce when it starts. I'll tighten the belt and take a look at the pad. Thanks!

Posted by Jack Ondracek (Member # 1466) on 07-21-2007, 09:00 PM:

Just covering the obvious. Oil on the pads is one of them. When you finished taking up the leader, do you turn the spindle key clockwise until it stops? (runup would do the same). Slack there would that bounce you describe.

Fast starting machines?

Posted by Monte L Fullmer (Member # 2797) on 07-21-2007, 09:23 PM:

little thing though: you can tighten the belt as much as you want to, but the clutch still has to be adusted to have the close amount of rotation tension (in inch pounds - and there is a procedure in figuring inch pounds with a fish scale, cord wrapped around the reel and measuring the pull when the reel is rotating, but forgot how much inch pounds are required for that size of reel..) for smooth takeup reel starts..by adjusting that outer nut/collar for friction disk/pressure pad adjustment.

There was one trick to to have the takeup spindle properly snug on the reel that I've seen: with machine off, reach back and pull on forward side of the belt so the spindle would take up any film/reel slack before machine start.

..and yes, if you've got fast starting machines (like the old Motiograph Mirrorphonic 7400 soundhead units) where you hit the switch and the machine takes off instantly, you really have to make sure everything is very snug.

once again - good luck.

Posted by Steve Guttag (Member # 268) on 07-21-2007, 09:38 PM:

Lately, I've been on a kick to get rid of all "Roundthane" type take ups. They never seem to apply even tension, take a set, fall apart, slip too much...and the list goes on. I'm replacing most of them with "V" type belts and the take ups have never been better and they last longer. Different soundhead/reelarm/magazine combinations take different lengths so you will need to measure...but that too will go a long way to eliminating bounce on take up.

As for clutch tension...stall the reel with your hand (not during a show, natch)...there should be a steady force coming from the reel...not a lunging type force. If it isn't steady...you have a clutch pad that needs to be cleaned/replaced/lubricated AND/OR your take up belt is contributing to the problem.

Once you have that sussed out...you want to have enough tension such that you have just enough tension to turn a FULL reel without bouncing on the holdback sprocket. The key is the least amount of tension that does the job. If you switch between 2K and 6K reels...I advise making a gauge out of anything that is handy to mark where the clutch should be set for each respective reel.

Lastly...what is the make/model of projector/soundhead and like wise for the take up system (And what type of drive mechanism is it to turn the reel)? This will go a long way to helping with the problem.

Posted by Louis Bornwasser (Member # 3063) on 07-22-2007, 10:00 AM:

The guys have covered it well except for one thing:

The reel. If the "floating" hub reels become dirty, worn or are not properly lubricated, they stop being a floating-style reel. This will also cause that kind of problem. Louis