Film-Tech Forum ARCHIVE: Century curved gate on Model CC

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Posted by Lindsay Morris (Member # 1430) on 12-16-2003, 05:03 AM:

Before many of the older hands jump in and say "toss it out and get a straight one" it aint that simple.
I am stuck with a curved gate and parts for these over here in sunny West Australia are a bit few and far between.
The Century "blurb" somewhere I read extolled the virtues of the curved gates as being the best focus set up for any cinema projector... but I am beginning to wonder about all that.
I have a random problem with the focus which pops in and out of focus most noticeably on scope and to a lesser degree on W/S.
I initially found that the curved lateral guides had a small wear on the shoulder where they sat upon the gate runners and this appeared to cause the film to wedge in there and buckle.
The wedging was purely random and the focus on the screen was all over the place like top LHS, bottom RHS a big spot in the middle. An even focus was almost impossible to maintain unlike the old Super Simplex's I had retired from service where I set it ONCE and vitrually never went back there again.
This thing drove me nuts.
I had the gate runners reground dead flat, the curved blocks also ground so all shoulders were dead square and the guy who did the grinding of these did a magic job on the curved face it is just like a factory set unit.
Assembled all the bits and using a brand new bit of film realigned the guides so the film was just held snug with a little bit of clearance and put it all back into the machine.
Ran a reel of scope film that I knew was normally good focus but RS on the Century previously.... result perfect focus [Big Grin]

I though problem solved but last week with a WS film the focus started to pop again and being a 2 feature weekend I watched the Sat night show closely (Chicago) and pin sharp focus edge to edge.
On the Sunday put the Friday night show back on and focus uneven.
A squirt or two of FilmGuard thru the holes in the MUT spool stopped it totally for the rest of the night.
The Manual section here covers the CC but NOT with a curved gate. Has anybody got any tips for setting these brutes up correctly as when they are running well they are quite good.
It seems strange that other machines from 8mm upwards all have at least one sprung side plate in the gate... the Simplex had none yet the Ballantyne has.
I am almost to the point of just opening up the side runners so the film just runs through without touching them much at all and so can accomodate a slight variation in filmstock width as the print of Chicago was done in the Rome labs of Deluxe and the problem print (Mrs Caldicot) was done in the Deluxe labs UK at Uxbridge.
It is obviously a lubrication or tightness in the gate problem as the slightest application of FilmGuard just to the edges of the film whilst it is feeding off the MUT stops it totally.
In fact one scope film that was subtitled had the subtitles slowly going out of focus, apply a bit of FilmGuard and as the treated section went thru the focus of the titles just drifted back in crisp and clean as if you were adjusting the focus knob.
Take the FilmGuard away and the focus slowly went back to bloody awful but that was prior to the clean up of the gate blocks and runners.
So what is the trick to setting up these curved gates ??

The entire upgrade to Xenon lamp, stereo sound with an ACL laser reader and the longplay of the MUT has gone very smoothly it is just this focus shift that is driving me batty.
Love the screen light. love the sound but hate the variable focus.
Lindsay

Posted by Stan Gunn (Member # 554) on 12-16-2003, 06:27 AM:

Hi Lindsay

A possible problem is lateral guide roller to tight for poly film I have found this problem on various machines.

I will send you my phone number direct should you wish to speak direct on this, easier than emails. [thumbsup]

Regards
Stan Gunn.

Posted by Warren Smyth (Member # 1838) on 12-16-2003, 06:48 AM:

Have you got excessive heat on the gate? Is there any sign of embossing of the film frame at the aperture edges? Water cooling may be required if you are using a high wattage lamps.

Posted by Mark Gulbrandsen (Member # 72) on 12-16-2003, 08:51 AM:

There are two alternatives other than fixing the problem at hand. One is the Kelmar trap assy which performs excellent to 3kw lamp size...its not available water cooled but could be adapted to be so. The second is to install an SA gate and trap with water cooled dovetail assy. Many dealers have lots of SA gates and taps laying around from doing Kelmar conversions and the parts can sometimes be obtained cheaply. The SA setup is hard to beat.
Mark @ CLACO

Posted by Steve Guttag (Member # 268) on 12-16-2003, 09:35 AM:

You won't find a manual for a C or CC with a Curved gate since they were not original equipment...you want to see an H or HH manual (the CC just means that it is a double shutter...likewise with the HH).

As to the "Studio guides"...DONT have them touch the film at all. Let the lateral guide roller do all of that work and it will do a great job. Normally there is enough slop to open the studio guides up so they wont touch if not...grind them down so they won't. From what you describe, that will probably cure your problem.

Putting an SA gate/trap assembly on can be a bit of a pain. In addition to the new trap dove-tail, you will need to modify your light guard...which is a big pain in the butt. However, the results when all complete are normally quite good. Mark may know off-hand if an SA light guard will fit onto a C frame.

Steve

Posted by Lindsay Morris (Member # 1430) on 12-16-2003, 04:51 PM:

Thanks Mark & Steve,

I have water cooling running and the whole trap assembly runs very cool indeed... without it the aperture plate was so hot after 15mins I could be hold it long enough to do a lens/format change "on the run" (I splice in 12 secs worth of blue film and change lens on a blue screen rather than stop and go again).
I suspect that this may have been a DI machine previously as the water jacket appears well used.
Will open up the Studio Guides and as Steve suggested let the lateral roller do all the work.
What I like about the Century is the ease at which bits come off.. just a couple of screws here and there and most parts are in your hands unlike the old Simplex that had bits that almost defied you to get them off. Century seem to have applied a rationale of improving access and maintenance unlike some others that never seemed to improve at all.
Not running a very big lamp on this replacement setup.. a 2kw lamp in a Lumex "yellow" lamphouse and just under 70 amps and the light on screen is very good (never measured it though) but the beam heat is a lot hotter than the old carbons ever were.
The lamp mirror is a goldish coloured metal unit and obviously NOT dichroic hence the heat but the water jacket controls that so no worries... worth the change for the improved screen image and no more reel changes.
Will post results of some readjusting shortly, thanks for input fellas.
Lindsay

Posted by Steve Guttag (Member # 268) on 12-16-2003, 06:01 PM:

The rule on the Century is that it is easy to work on...because you will have to! Simplex is a more precise machine but as you say more difficult to work on...especially for the un-initiated (particulalry on the pre XL machines).

I can't tell you the last time I needed to change a Simplex XL main drive gear, shutter drive gear or intermittent drive gear...on the Century...one of those happen about once a month in our service area...somewhere.

Steve

Posted by Scott Norwood (Member # 30) on 12-16-2003, 06:09 PM:

For whatever it's worth, I sent Brad a copy of the Century H manual and it will probably be available on this site soon.

Posted by Mark Gulbrandsen (Member # 72) on 12-16-2003, 11:31 PM:

All of the SA stuff will bolt right onto a C frame without any alignment or such, except fo the gate clearance adjustment. he light shield is also a bolt on thing. Only a small notch for the door clasp needs to be cut into the shield.
A properly working solid curved gate and trap can work very well when everything is just right. It can also be hell to ge tit there [evil]

!! The advantage on the SA trap is auto equalization(even pressure) of the trap bands. Works the same as on an X-L curved trap.
Mark @ CLACO

Posted by Steve Guttag (Member # 268) on 12-17-2003, 06:11 AM:

Mark,

I seem to recall a clearence problem with the intermittent spocket when an SA trap is fitted to a C frame...that the sprocket can crash into the bottom of the tension bands if framed all of the way up.

Steve

Posted by Lindsay Morris (Member # 1430) on 12-17-2003, 06:51 AM:

Scott,

Yes I can see that the Century HH manual is almost at the point of Public access so another couple of days and I will be able to download that and go over the gate bits and pieces.
Thanks for supplying that manual.
I am really curious of the rationale behind these fixed side blocks on the Century.. they do of course provide the curve to the bands but are they really supposed to be a lateral guide??
The old Simplex never had any side weave and probably had a slightly steadier picture than this CC but it will take me a while to get all the bugs out of things.
Steve mentioned always having to pull them apart but of those that I have seen in operation the Century's have always seemed a solid reliable unit and made much more uncluttered than the old Simplex which is a product of evolution I guess.
However it great to be able to just unbolt almost all the bits from the operating side and give things a really good clean and then get it all back in place with no problems as most bits are nicely dowled so they drop back in exactly where they should.
Time will tell just how reliable it turns out to be but with only a summer season of around 80 odd sessions I reckon it will go a long long while between major surgery events.
Will try the suggested setting of the blocks this weekend and see how it goes.
Thanks for all the info.
Lindsay

Posted by Mark Gulbrandsen (Member # 72) on 12-17-2003, 07:48 AM:

Steve,
You're right about that, the C has a bit more framing adjustmet available than the SA does. Its an easy to cure problem though by simply screwing a small spacer to the film side top of the intermittent carrage, or just a hardened steel stopper screw. Cinerama 35mm heads had an adjustable stopper screw at each end of the travel.
Mark

Posted by Dick Prather (Member # 1136) on 12-17-2003, 10:47 PM:

Lindsay,
The studio guides were designed to bring film side sway down to a gentle weave making it less objectionable. Simplex E-7 and
X-L flat gates had them but in fixed locations. Century guides can be moved. Century C's had a shorter trap and unless they were set properly had some side sway. Steve is correct let the guide rollers do the job not the studio guides. Almost sounds like a buckling problem in the film trap.

Suggestions:

Make sure the guide roller lines the film properly to the intermittent sprocket.

Make sure the studio guides are not grooved, or placed too close together causing the film to slightly buckle or catch in the guides. I believe the H guides were also reversible so 4 sides were available.

Setting them wide should prevent this.

Set film tension only tight enought to keep the film steady in the trap by moving the lens assembly back and forth. The C's were 2 film thicknesses from the guides to the gate when closed. I forget what the H spacing was.

I did do a couple of rebuilds on Century C projectors with a SA trap & gate. Only problem I remember was I needed to make a gate stop. The normal gate closure caused way too much film tension. The framing carrage problem was already taken care of.

Posted by Mark Gulbrandsen (Member # 72) on 12-18-2003, 06:43 AM:

Dick is right about the studio gides. I normally remove them from both Century and Simplex machines and put them in the verticle file. Also makes cleaning the trap much easier. The picture is always far steadier too.
Mark @ CLACO

Posted by John Pytlak (Member # 331) on 12-18-2003, 12:48 PM:

In a 35mm, lateral positioning should always be done by the lateral guide roller, with the "Reference Edge" of the print being gently pushed against the fixed guide roller by the spring-loaded one. The "Reference Edge" of a 35mm print is the edge along the analog soundtrack side of the film, and the lateral guide roller is usually at the top part of the gate assembly, just above the aperture.

The idea is that when printing the film, the printer positions the printing negative and raw stock using the "Reference Edge", and then the processed print is positioned during projection using the same edge. This allows "cancelling out" any dimensional variation leading to a steadier image, otherwise known as the "principle of cancellation". See the paper "Challenges to the Concept of Cancellation" by Roland J. Zavada, published in the December 1981 SMPTE Journal, Volume 90, page 1173.

"Pinching" or "skewing" the film, or having multiple contact points with the edges can lead to problems with steadiness or focus stability.

Always be sure the lateral guide roller is turning freely, and that the spring loaded side is free-moving and just gently pushing on the non-reference edge of the print to position the reference edge on the fixed guide.

Posted by Steven H. Krams (Member # 1461) on 12-20-2003, 05:04 PM:

Here is a new slant on this problem. Century Model C or CC projectors came in two varieties. Most had a 70.6mm lens holders. In 1955 the projector was redesigned to accmodate 4 inch lenses. This lens proved to be of poor deisgn and after a few years the poor design resulted in the lens sleeve becoming worn, cocked. In addiiton the vernier focus screw developed high spots. After many years some of these actually froze up. The result was that the lens holder was not flat across the surface of the holder and so focus shift became a serious issue with this machine. It would sometimes focus well and hold focus and other times it would not depending on position and heating. Over the years as these machines came into our facilties we converted them A type frames (Sometimes referred as the model SA, SAW,DA,DAW and so on.) This required some machine shop work be done to the frame to accmodate the SA Lens holder, light shield, shutter guard, trap and gate system. The results were excellent and many of these units which we upgraded are still in service today. The last time we did this conversion for was for an 8 Plex in Manilla that had 3 machines in each booth in 1996. The result of the failed Model C with 4 inch lens holder was the evoloution of the H Frame and then the A frame. Today one can observe many changes which have been made to the main "A" frame casting so that there is not much resemlance to the original design which was discontinued when the plant plant in Long Island City moved to Lakewood New Jersey in the early 1980's.
So much for History!

Posted by Lindsay Morris (Member # 1430) on 12-23-2003, 04:25 AM:

Thanks everyone for the various inputs... some quite interesting reading re the evolution of the Century C and others.
The last weekend sessions went well with no focus shifts that I saw or had anyone rushing into the box complaining about the focus (box is on ground level in an outdoor venue... so always plenty of lookers).
Film playing was Italian Job and being in scope using the full frame I felt any problems would show readily. Even the odd subtitles across the bottom were well focussed unlike another scope print earlier on in the season which the subtitles only came into focus after some Film Guard was sprayed on the MUT feed spool.
Took the studio guide blocks well out and slightly overdid the lateral roller as I had a bit of DTS roaring down the black LHS edge until I dragged that back.
The Century CC I have is nothing like the CC in the manual when it comes to lens barrel etc (which is the 100mm diam type).
It is almost a direct copy of the H machine after looking at the manual of which I downloaded from the manuals section.
This Century is branded Westrex on the proj & soundhead door glasses but has a big label on the front clearly saying Century CC and yet the soundhead is labelled Westrex R but is EXACTLY as per the soundhead shown in the H manual.
So what is it???
My best guess is that it is something in the middle of the evolution of the C to the H series that Westrex brought into this country under their own label but made by Century in USA.
Bearings and gears I ordered from the C manual info all fitted perfectly.
Later on in OZ Westrex bobbed up with an Australian made machine called CENTREX and there are quite a few of those about still going strong.
It remains to be seen whether or not this 100mm barrel gives any trouble but focus control is very smooth and when things were going well during installation tests focus was pin sharp overall and as good as or better than the old Simplex girls it replaced.
There is some variation in film stock widths which when I set it all up was quite happy with the studio side guides as set.. but! run another print and all hell broke loose if it was just a "bees knee" wider than what I had used to set things up.
So just how much variation is allowed for in 35mm film stock.. John P any info on that??
See how this weekend goes with a WS film from a different lab to Italian Job. Plus a few odd trailers thrown in for good measure all from different sources.
Have a great Xmas all,
Lindsay

Posted by Stan Gunn (Member # 554) on 12-24-2003, 07:28 PM:

Hi Lindsay.

Regardles of the type of gate in a machine the most important thing is gate tension. 30 years of projection and service enginer have taught me that the obviose is most likely not the cause of the result.

With a curved gate low band tension is the best, as if the tension is tight the film will pull into the centre.

latral guide rollers if the spring tension is to tight can also do the same, causeing focus problems at the bottom of the screen, (plays hell with subtitles).The rollers must be perfectly alighned to the intermittant sprocket,and these days have the tension set for poly film just eneough side tension to hold the film steady. Any way call me for any info you requiere in the future.

regards
Stan Gunn

Posted by Lindsay Morris (Member # 1430) on 01-05-2004, 03:43 AM:

Dare I say it??
Looks as though I have got rid of the shifting/popping focus problems as now after 2 weekends of screenings I have not yet seen any shifts like I had done previously.
Thanks for all the advice from everyone as by sifting thru all that plus going thru the Century HH manual I have pretty well got it all sorted out.
In addition I have confirmed that this branded CC machine is not really a CC but something of a hybrid with a bit of the CC like the shutter housing (round) and the big 100mm diam lens barrel from the H series.. plus the curved gate.
I have seen a few of these machines here in OZ and they are certainly different to the C series shown in many of the "Picture" segments on this forum. The door is identical to the H series and the logo is Westrex and NOT Century so these machines are somewhere between the 2 series.
What I have done is to:
a. Taken the side runners well out so that there is quite a wide clearance between the edge of the film and the runners.. at least 1mm.
b. Set the soundtrack side runner so it was dead true and in line with the gate lateral roller and made the extra clearance on the non soundtrack side which is how the Balantyne is set up with its sprung side runner. The "reference side" as described by John P.
c. Over the 2 week period slowly backed off the gate tension night after night and after each adjustment went down to the front row and studied the image movement.
Now the tension screws are practically backed right off and the image is quite stable.
They obviously had been wound right up by whoever previously owned the machine and when they were like that you could really hear the intermittent working real hard to move the film.
Now it is just a gentle purr.

The lateral guide seems to still have far too much tension for poly stocks yet older acetate stuff runs thru quite flat.
Short of snipping some coils off the tension spring is there any easy way to reduce that tension???
The poly film really bows and jiggles about quite violently and noisily as it goes into the gate assembly... acetate stuff just slides in with no noise and spreads the rollers and lays flat against the runners.
One of the old Westrex soundheads (206A) that I have retired had a similar problem with the tiny lateral guide roller just above the fixed sound gate (one of THOSE with NO rotary stabiliser shown on a post sometime ago from an old theatre).
To fix that I snipped small bits off the coil spring bit by bit until the poly film would lay flat and let the guide roller spin rather than stay stuck and develop a series of grooves which then made the film jump about and sometimes create a sort of flutter in the sound.
Those old Westrex girls had HUGE flywheels and massive bronze bearings and after god knows how many years of use there is still virtually no play in those bearings. Never heard any wow.. the occasional flutter as above and the only problem was that when the motor was switched off the machine tended to run on for quite a time before it came to a stop. This could be a real cow if you had a film break and a build up inside as it just did not want to stop.
Lindsay

Posted by Stan Gunn (Member # 554) on 01-05-2004, 11:31 PM:

Hi Lindsay

Shorten the lateral roller spring so that it doesn't affect the poly film anything else from nitrate to acetate will be no problem.

Theres nothing wrong with 206s I run a pair of 208Bs with C&W EH seniour heads.
All your fixs were spot on , you should now have many hours of happy screening ahead of you.

Stan Gunn. [beer]

Posted by Lindsay Morris (Member # 1430) on 01-06-2004, 05:14 AM:

Stan,
Thanks for that... it does seem a bit crude as I thought at the time when I snipped the Westrex springs up to reduce the lateral tension.
But I guess short of finding another slightly weaker spring that will be the only answer.
I will give it the chop tomorrow when I go to the cinema to mow all the damn grass that grows like crazy in patches and dies back in others.
Have another scope film this weekend so any focus variations will be obvious as this print is also poly.
Lindsay