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» Film-Tech Forum   » Operations   » Film Handlers' Forum   » The "perfect" threading procedure (Page 1)

 
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Author Topic: The "perfect" threading procedure
Monte L Fullmer
Film God

Posts: 8301
From: Nampa, Idaho, USA
Registered: Nov 2004


 - posted 02-19-2006 02:35 AM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
Okey - time for another "show and tell" and this is is simply for what its worth:

We all know (or supposed to know) that distance between picture and sound is 21 frames with the sound ahead of the picture.

 -

..and the sound blip almost straight across from the LED assembly:

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With these frames in their correct position, this becomes the "perfect" loop size for every machine that is out there.

Now, this is just for the well-known SIMPLEX XL/35 beauty that we either love or hate to death. In any case, we're stuck with this machine that has been with us since 1950. So, we'd better make the best of it.

When the frames mentioned above are in their right places, the loops become the 'perfect' size, as thus:

The Upper Loop -

 -

Now, I'm going to stop right here and explain something to you locations that have the curved gate variety:

1- Notice that the loop is entering the trap and gate assembly in FRONT of the band - not above the band.

With the film entering like this, the film, being made of our favorite abrasive material called 'polyester', there is less wear on the band since the film is parallel with the band on entry. If the loop is too big, the loop of film is ABOVE the band and contacting that upper round corner of the band. When the loop is like this, this oversized loop is putting massive wear on the top corner of the band wearing it down like nobody's business (anyone here had a band snap during a performance due to this...it ain't fun.. [Smile] )

The Lower Loop:

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Now, heres's were I'm going to get some argument from quite a few here: I'm sure that a great deal of us have been trained that the lower loop is to be where the back side of the loop is a finger's width from the film to the back compartment.

Really, nothing wrong with that, but...how many of us love sports, especially the individual sports like golf, tennis, racquetball - anything that we have to it a ball with a device. Now, we know that with this form of sport, that if the ball is hit in a certain area of the device, the ball is hit true and the player doesn't even feel the hit after the followthrough...this is commonly called "the sweet spot"

..projectors have "sweet spots" as well and that is the 'correct loop size'. You make the loop size just right, the machine will run so much quieter to the point of the platter will be the one that one hears more than the machine. If one can hear the platter over the projector, then the lace job was a good one.

Thus, with the loop size only being a quarter-inch from the back wall, the film is leaving the intermittent sprocket in a straight line-not bending down and being a bit stressed as well.

In the picture above, there is a trick to do this every time one laces a machine: Notice where the frame line over the middle constant sprocket compared to the loop size. The frame line is almost at the 12:00 o' clock position. (I use that metal dowel spot, which is inbetween the two pad rollers on the pad arm assembly as my center point for the lower loop set) How we achieve this position of frame line and loop is to set the intermittent sprocket JUST AS THE SPROCKET has FINISHED TURNING.

We all know, when the intermittent sprocket has finished turning, the lower loop is at its largest size. The same with the upper loop - loop at the smallest size, AND the trick to this upper loop size is just the opposite in the pict below:

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You notice that the frameline is at the 6:00 o' clock position. AND ... this pict is from the flat gate variety.

Important thing about flat gate Simplexes: that upper loop had better be as big as what's shown in the pict due to the fact that the rail top ends that stick up in the gate assembly DO NOT like small loops. You build a small loop, the splices will pop and snap as they head down into the trap assembly. These assemblies love to bust splices, especially weak ones if the loop is too small. AND, if the loop collapses, it will shear off the teeth from that driven fibre gear due to the sprocket will suddenly be pulled foward by the film when the loop is either too small or collapses. And those rail ends act like a fulcrum for the film to pull suddenly when the loop is too small and jerk on the sprocket, and shredding the teeth off that gear.

Thus, the trick is to have the loop tall enough so the film is heading straight down, after leaving the loop, into the trap without any bending or looping whatsoever. One could build the loop to where it about a quarter inch taller than the sprocket with the frame line at the 6:00 position - with the intermittent sprocket being stopped right after it gets into the locked position.

In short, if you would like to have a much quieter booth, try this out for size. It's amazing that the 6 plex that I work at, the machinery runs so smooth and with a steady 'purr' from these 1050's if laced up this way.

Anywho....for what it's worth to all.

And I'm sure that this technique is for all brands of machinery, for this is the only brand that I have available to demostrate this technique.

thx - Monte

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Thomas Dieter
Expert Film Handler

Posts: 234
From: Yakima, WA
Registered: Jun 2004


 - posted 02-19-2006 02:56 AM      Profile for Thomas Dieter   Email Thomas Dieter   Send New Private Message       Edit/Delete Post 
WOW!!!!! This is Good Stuff Monte! I have to thank you for this information. Maybe I can not officially find the sweet spot. Thing is attempting to adapt this to the V-4s I use when it comes to the top loop.

You learn something new every day.
--Tom

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Stephen Furley
Film God

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From: Coulsdon, Croydon, England
Registered: May 2002


 - posted 02-19-2006 04:51 AM      Profile for Stephen Furley   Email Stephen Furley   Send New Private Message       Edit/Delete Post 
The sound of a projector, or other mechanical device, is certainly a good indication that everything is ok. In a previous job we had three inter-connected rooms, with the doors between them left open during the day. In the room at one end was a small offset press, and I was in the room at the other. I called to the operator to tell her that she was getting too much ink on the rollers. She was amazed, as I couldn't possibly have seen the machine from where I was; but I could hear it. I had much more experience on the machine han she had at the time, and the difference in sound was obvious to me, but she hadn't noticed it.

Remember that it will be necessary to adjust the lower loop size in very large auditoria. A well-designed projector will be able to accomodate this variation in loop size.

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Thomas Jonsson
Expert Film Handler

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From: Bromolla, Sweden
Registered: Sep 2003


 - posted 02-19-2006 05:23 AM      Profile for Thomas Jonsson   Author's Homepage     Send New Private Message       Edit/Delete Post 
On my Vic 5 I can hear no difference if the loops are large or
small. I have the curved gates with the "pushers" above the gate
removed. This way I have reduced two extra bends of the film to
one. If the upper loop is large (not too large!) I need less
tension on the bands, and the wear on the rounded part of the bands
is a little less. I also use velvet bands, which makes the machine
run smoother. The curved gate gives a better image than the
straight one, but I dislike it dearly.

Thomas

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16151
From: Bountiful, Utah
Registered: Jun 99


 - posted 02-19-2006 09:03 AM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
Dr. Monte.... Excellent post! And great job explaining it all....

quote: Stephen Furley
A well-designed projector will be able to accomodate this variation in loop size.

Of course it is important to properly thread any projector but in some ways I absolutely agree more with that statement!

Some machines are very unforgiving of loop size and will either cause undue wear to the bands or damage to the print.... many Strong versions of the Smplex are this way as is the Someplex 35/70... the latter HAS to be excact or it will damage the print. The JJ running 70mm is also this way to a large extent but ifs more forgiving than the Simplex is. Strong has come out with way too many gate/trap variations and the moving of the sprocket upwards to accomodate the lens turrett was another blunder on theor part as there is not really a correct upper loop size for this version of the Simplex that does not induce extra wear to the bands and still allow the full range of framing...... The many reasons why I never liked the Pot Metal X-L are merely reinforced by the poor gate/trap designs of Strong.

Mark

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Scott Norwood
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From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99


 - posted 02-19-2006 09:08 AM      Profile for Scott Norwood   Author's Homepage   Email Scott Norwood   Send New Private Message       Edit/Delete Post 
Nice pictures, but that lower loop is definitely too big, unless you have a screening room or tiny theatre. My method for threading Simplexes (X-L/PR-1014) is to make the upper loop such that it is even with the top of the upper feed sprocket when it is at is largest size (right before pulldown). I usually make the lower loops a few perfs smaller than the one pictured, depending upon the size of the theatre. For soundheads with two sprockets (RCA-1040/9030/9050 and SH-1000), I like to make the loop in the soundhead fairly large.

Mark--I've noticed that too--when threading the Simplex TU-2000 (recent turret model) as above, the upper loop is much higher in relation to the bands than it would be on the PR-1014/X-L. Should one compensate by making the loop smaller?

So who is going to start the debate about threading over or under the black plastic roller below the intermittent on a JJ, and whether it is to be threaded the same way for both 35mm and 70mm? (I've seen different Century manuals which specify different approaches to this.)

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Frank Angel
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From: Brooklyn NY USA
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 - posted 02-19-2006 10:54 AM      Profile for Frank Angel   Author's Homepage   Email Frank Angel   Send New Private Message       Edit/Delete Post 
I've seen lots of guys making that top loop huge. Never could figure out what the penchant for that was. Evidently they are too young to have ever worked a Super Simplex with that upper loop sensor from hell that would slam down the fire shutter if the loop hit it. You learned fast enough that the loop had better not be oversized.

And Scott is right, the loop out of the gate really is determined 100% by the size of the theatre. I've got a 2500 seater to contend with and setting that sound blip at zero off-set or "absolute sync" will make lip-sync go into the toilet for most seats in the house. Sound sync for large houses has to precede the image rather than be at zero off-set. The general rule-of-thumb is that you need to set lip-sync to happen at about 1/3rd back from the screen, not AT the screen.

I always wondered how they picked the 21 frame off-set which gives very little wiggle room for the large theartres. I can't imagine how small that loop has to be at Radio City Music Hall. And in the day, when there were lots of single screens with very large rooms -- 3000-4000 seaters -- the need to have sound sync precede image was real. I guess with the proliferation of much smaller rooms, many smaller than screening rooms, it's a moot point. Although there are those exceptions. Our outdoor venue (6000+ seats/spaces) needs a super short loop. Boy would I love to have a longer sound off-set.

And then there is that issue of sound and image NOT exactly at that proper offset distance. I have seen quit a few prints where it is obvious just by looking at the soundtrack start point and the image picture start frame that they are not printed together correctly, sometimes off by two or three sprocket holes. John P. says that matching the negs is quite difficult in the darkroom.

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Mark Gulbrandsen
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From: Bountiful, Utah
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 - posted 02-19-2006 11:17 AM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
quote: Frank Angel
I always wondered how they picked the 21 frame off-set which gives very little wiggle room for the large theartres. I can't imagine how small that loop has to be at Radio City Music Hall. And in the day, when there were lots of single screens with very large rooms -- 3000-4000 seaters -- the need to have sound sync precede image was real.
Frank,

Didn't you know that back in those days those booths were equipped with Western Electric DSP based Digital Sound Advancers...... [Big Grin] .

Mark

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Brad Miller
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From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99


 - posted 02-19-2006 01:17 PM      Profile for Brad Miller   Author's Homepage   Email Brad Miller       Edit/Delete Post 
Scott, I've been playing with the JJ roller on threading over vs. under. I've found that acetate film seems happier threading under and polyester film seems happier threading over. Due to the natural curve of these films, following that practice also guarantees that if you are running an overly curled print that the roller cannot come into contact with the picture area.

For 70mm of either base, I always thread under.

One thing that irks me about this is there are many variations in spacing on this roller from machine to machine. Also the slap guard rails (not very common) are located in different places too. [Roll Eyes]

 -

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Monte L Fullmer
Film God

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From: Nampa, Idaho, USA
Registered: Nov 2004


 - posted 02-19-2006 01:38 PM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
Scott, I know that you disagree, at least, give it a try with my bottom loop size...you might just be suprised. If you don't like it, it's your choice, of course.
quote: Scott Norwood
Should one compensate by making the loop smaller?

..the Milleniums, with this raised upper sprocket, has the huge disadvange of wearing off the tops of the bands, when the loop was made the "normal" size, very horribly since that sprocket, being raised wasn't moved forward in the same distance as well so the loop size could be kept at the same ratio.

Thus, I do my best to maintain a much shorter loop so the film still woundn't be wearing on that corner of the band.. and it can be done with no qualms about having a upper loop too short.


Remember even with the machine running that the loops are only going up and down in a quarter inch span (with the simplex.. - as for other machines, in which I would love to try this out on century's and the P-35 Christies, in which I made those lower loops one sprocket after they touch that roller on that middle sprocket assembly...) so there really isn't that much worry of scratching unless one builds gigantic loops for some dumb reason.

Granted, the 21 frame count is at the speaker on stage. I believe that a one to two frame advance shouldn't affect the diagrams above due to the slack that is already there below the projector...and since this variable of film length to the soundhead is AFTER the middle sprocket, thus the above demostration that I posted can still be used.

Yes, the Supers and the E-7's - get that loop up there since these machines had that 'shute' assembly under the sprocket to make sure that the upper loop was tall enough, but not to hit the firetrap sensor, especially if an out of frame was encountered..

Thomas - on your V4e - there can be a simple way to figure this out and that is: take a leader with these markings, put the "picture start" in the trap, and go ahead and lace up the machine WITHOUT making your loop after the intermittent sprocket. Thread the machine as normal and when just before securing the film over that last sprocket, back the film up til the sound blip is in the designated area. I bet that the frameline will be at the 12:00 position on that last sprocket. Lock the roller down and then see if your lower loop, when pulling the film back is the correct size.

Then, for the upper loop, do the same with the frameline at the 6:00 position. See how this turns out, for this is the way I always threaded any Cine V(x) machine - where the 4E's and the majority of the V5's were the flat trap variety.

-thx a bunch, all ... - Monte

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Mark Gulbrandsen
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From: Bountiful, Utah
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 - posted 02-19-2006 02:47 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
quote: Brad Miller
Also the slap guard rails
The slap guard rails on a JJ are actually a very good addition. They were originally put on Showscam JJ's to help with loop slap which gets VERY violent at 60 fps! I used the 35mm section of one of those rails on my VistaVision projector to eliminate the same problem and those slap rails are one of the main reasons why my VV is very easy on film and runs quiet. I've run loops through it literally thousands of times without damange. Not many other VV machines can claim that feat.

Mark

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Steve Guttag
We forgot the crackers Gromit!!!

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From: Annapolis, MD
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 - posted 02-19-2006 05:25 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
The actual lip sync s supposed to be 21 frames...however, the leaders always put the sound start a mere 20 frames in advance so you have a 1-frame built in. This is about 42msec of difference from dead sync. Using "Kitchen Physics" let sound travel at 1msec/foot (it actually depends on the humidity and such...generally 1130ft/sec is the nominal speed though). That makes for 42 feet of pre-compensation built in (or 47-feet to be more precise.

One thing else to consider is the psychoacoustics of the problem. The human brain can deal with sound lagging behind the picture...it deals with that all the time when dealing with people talking at a distance...it can not deal with sound LEADING the picture...that will always appear to be out of sync long before sound lagging the picture. The DCinema people found this out pretty fast...the latency (time it takes to process the picture) in a typical DCinema projector is approximately 85msec or 2-frames. The brain will immediately say that is out of sync. We have had to install audio delays on video sources that can ensure that the sound will be in sync. Dolby's DMA-8 has a "Global Audio Delay" to also deal with this.

So back to the problem. When all of this 20 versus 21 frame business came out, the theatre sizes were much longer, for the most part and the 47-foot pre compensation worked pretty well. Shifting a couple of perfs either way will get you half that time in shift so you have between 70-feet and 23.5-feet. So the system works the bulk of all theatres constructed. Again, when in doubt, make the lower loop larger to ensure you don't have the sound preceed the picture for the bulk of your audience.

Note too, the "Academy" leader has that diamond throughout...you can thread up on just about any number and look for the frame with the diamond to see where you are.

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Monte L Fullmer
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From: Nampa, Idaho, USA
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 - posted 02-19-2006 07:49 PM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
..were slap rails a default install on new Century's? We're they on just the "JJ" models, or on all models?

For I've never seen these before.

(this is what happens when you don't work with all of the models out there and get stuck with just a few in your lifetime as projectionist...one doesn't know all - a big disadvantage when wanting to help out others...)

thx-Monte

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Steve Scott
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 - posted 02-19-2006 08:18 PM      Profile for Steve Scott   Email Steve Scott   Send New Private Message       Edit/Delete Post 
I've only seen them on JJ diagrams. Thanks for the tip Monte, it really reduced the noise bleed from the booth behind our big house when I tried it tonight.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12134
From: Annapolis, MD
Registered: Dec 1999


 - posted 02-19-2006 09:43 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
The JJ Slap rails came out under the ORC era of Century projectors...I know they were on all new machines by 1987 (and probably a year or two prior at the most). They were part of the demise of the R50 soundhead. With the slap rails came the slot in the front of the projector for the 70mm film to exit and then go around the outside of the optical soundhead (R3) wich is 35mm only.

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