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Posted by Bernie Anderson Jr (Member # 410) on 04-25-2001, 11:31 AM:
Okay here's another one, I just got the super on the 9050 running yesterday. needs alittle help but not bad. Anyway, I'm running with hour reel arms (Kelmar adjustable) with roundthane belts And I've seen my friends projector do this too. On start up it pulls the bottom loop hard in the RCA9050 and looses the loop. Now I know it's the take up belt. But how do you guys go about measuring these belts out since they have to be cut? Mine is obviously too tight, I guess I blew that belt. But how loose do you guys start with the belts before cutting. Is there a hidden secret?
Posted by Scott Norwood (Member # 30) on 04-25-2001, 11:37 AM:
It sounds like you have the takeup tension set too tight. Loosen the screw (the one that controls the spring tension) on the takeup arm. The film shouldn't "snap" or be pulled tightly at all on startup. The belt itself should be tight. There may be a precise way to set the tension, but I just do it by feel. The film should wind snugly but not super-tight through the entire length of the reel. The tension adjustment is more critical for large reels than for small reels.
Also, if you're using large reels, you should be using a floating-hub reel for takeup, not a solid-hub reel. The idea with the floating hub reels is that the hub can come up to speed very quickly, without allowing much slack to develop, which would stretch or break the film on startup.
Posted by Brad Miller (Member # 2) on 04-25-2001, 01:57 PM:
In addition to loosening the takeup tension, when you thread make it a point to manually advance the projector by hand until the take up reel "catches" the film tightly instead of just threading it at the point where you would start. This can save an awful lot of startup bounce as well, but concentrate first on that takeup tension.On that RoundThane belt, it shouldn't be fitted too tightly, but not loose enough that it can't jump the pulleys either.
Also, please refrain from using "teaser" subject headers in the future. This is in the FAQ and makes surfing the forums and searching the archives difficult.
Posted by Barry Hans (Member # 477) on 04-25-2001, 02:05 PM:
I have always set the take up tension by placing a reel full with film on spindle and on start up of projector reel should just start to rotate- slowly. That is a good starting point and can be adjusted as needed from there.Good luck!
Posted by Mark Gulbrandsen (Member # 72) on 04-25-2001, 05:31 PM:
Sounds to me like you are using solid type large reels. These will typically do that when things reach speed. If you go to floating hub reels this problem should go away. Also install a VKF sprocket in the RCA at the holdback position. This will afford far more safety for the film perfs. A sprocket costs far less than a film does
Mark @ GTS
Posted by Gordon McLeod (Member # 33) on 04-25-2001, 08:51 PM:
Also it usually caused by the projector starting too fast and the film going slack to the take up for a moment and then the takeup catches up with a jerk
Try putting a 250watt 1-2 ohm resistor in serries with the motor to slow the startup down
Posted by Leo Enticknap (Member # 534) on 04-26-2001, 08:39 PM:
One thing I'd add is that if you are using any 'house leaders' made from acetate stock with a motor that has a tendency to ramp very quickly and pull hard at the sprocket just past the intermittent loop, then bin them and make some polyester ones.If yours is an extreme case then the stock might still jump over some sprocket teeth and cause loop loss (and as Scott and Mark both pointed out, solid-hub spools will increase the likelihood of this), but it won't break and this should give you the chance to adjust the take-up tension so that the loop will 'survive' the startup.
I once had problems with a Fumeo HL3000 (16mm) mech breaking brittle old acetate prints on startup. We didn't have any floating-hub spools, but a combination of polyester spacing on the start and manhandling the 6,000ft take-up spools up to speed eventually managed to solve the problem. Thank goodness I never had to do a changeover with this arrangement!
Posted by Paul G. Thompson (Member # 655) on 04-26-2001, 08:43 PM:
In addition to inching the machine forward, I found that giving the reel a little gentle push on startup was very helpful. It is possible that the reel is slow starting, then builds up enough inertia to jerk and lose the loop. Gordon is right on the money about that. However, the the motors on the 9030's and 9050's ramp up slowly, and I don't think the resistor is really needed.
Although the loop can easily be restored "on the run", it is still an inconvenience. It would also suggest that the holdback sprocket may be worn out, and/or the pad roller is grossly mis-adjusted.