Film-Tech Forum ARCHIVE: Aperture plate filing

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Posted by William Dickson (Member # 314) on 01-27-2000, 04:43 PM:

I recently noticed that many of the appeture plates in our theater need some minor filing. The projected images have slight inward bulges on the sides. It doesn't appear to be caused by scope lenses not alligned properly. Any tips on how to file the appeture plate would be greatlt appreciated. Also what type of file should I use?

Posted by Dave Williams (Member # 299) on 01-27-2000, 06:54 PM:

Use a nail file. Most files from the hardware store are so heavy they will file the shit out of it.

------------------
"If it's not worth doing, I have allready been there and done it"

Posted by John Walsh (Member # 168) on 01-27-2000, 10:42 PM:

Did you mean the 'shadow' bulges inward, rather than the 'image?'

You might find that cutting a strip of emery cloth and lightly running it on the opening edges will remove just enough brass to clean any shadow away.

Posted by Brad Miller (Member # 2) on 01-27-2000, 11:39 PM:

If you absolutely MUST file that plate a bit, go spend some bucks on some real aperture files. The files you can find at Sears are rough on all edges, and while you are working on a corner, you will be cutting into the next side! Also, remember if you're wanting to open up the top right corner as it is projected on the screen, you want to cut on the lower left hand corner of the plate, as the lens flips the image.

Before you go cutting on a scope aperture, check out the "Focusing Anamorphics" tips on the front page of this site. Many times the focus will get just a touch off and will "shrink" the image on screen to produce a shadow.

Finally, remember that once you file, there is no way to put what you cut back! So be reeeeeal careful.

Posted by John Pytlak (Member # 331) on 01-28-2000, 09:16 AM:

Whatever you do, always use the SMPTE 35-PA (RP40) test film to verify that you are projecting as close as possible to the correct image dimensions.

Per Standard ANSI/SMPTE 195, the projectable image area for "scope" is 0.825 X 0.690 inches (20.96 X 17.53 mm). The projectable image area for non-anamorphic (1.85:1 aspect ratio) is 0.825 X 0.446 inches (20.96 X 11.33 mm). The 1.66:1 aspect ratio is 0.825 X 0.497 inches (20.96 X 12.62 mm), and the "Academy" 1.37:1 aspect ratio is 0.825 X 0.602 inches (20.96 X 15.29 mm).

Test films and standards are available from the Society of Motion Picture and Television Engineers, http://www.smpte.org

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

Posted by Martin Frandsen (Member # 74) on 01-28-2000, 02:02 PM:

I do not have a loop of RP40 test film, but i found some RP110, i think its for the same use, checking correct image dimensions when you have been filing appeture plates, it shows the different aspect ratios.

Posted by Gordon McLeod (Member # 33) on 01-28-2000, 02:08 PM:

Get a set of needle files for the fine work and Iuse an AugerBit file for the course work

Posted by John Pytlak (Member # 331) on 01-28-2000, 02:30 PM:

Martin:

Some of the SMPTE 35-AT (RP110) test film that is in circulation is quite old, and was made before the current dimensions were adopted. In particular, the anamorphic image width has been narrowed from 0.839 to 0.825 inches, and the anamorphic height has moved from 0.715 to 0.700 to 0.690 inches. Using the old dimensions risks showing the DTS track on the screen, and will show more "flashes" at splices.

I believe SMPTE is updating RP110 and the 35-AT film to agree the current dimensions specified in ANSI/SMPTE 195 and RP40.

I suggest you get some new SMPTE 35-PA (RP40) so there is no question.

Posted by Randy Stankey (Member # 64) on 01-28-2000, 05:39 PM:

I have had some apertures that have those little humps in them. They look like dust bunnies that won't go away when you clean the aperture.

If that's what you have, may I suggest using an emery board nail file?

I find that they have just enough 'bite' to get the burrs off the edges of the plate without the risk of over-filing and ruining the plate.

Ask one of your box office cashiers for one. They have LOTS of them!

Posted by Rick Long (Member # 213) on 01-30-2000, 06:54 PM:

Many technicians, over years of installing projection equipment, have developed a theory which states that light enlarges the hole in the aperture.

This must be the case. When we leave a theatre, the plates fit the screen perfectly. When we go back to the theatre, a month later, the picture is on the masking in many cases. Although there is a cheap file covered in brass dust on the port-hole ledge, the projectionisit invariably denies that anyone tried to improve on the plate.

Thus, light wears holes in aperture plates.

Posted by John Walsh (Member # 168) on 01-30-2000, 08:02 PM:

Yes! The light photons push the brass filing away from the projector....

In this part of the universe, however, I find that the hole gets smaller. I think the action of getting hot, then cold, then hot, etc. closes the hole slightly.

Also, in new theaters, as the floor settles, the projector might tilt down just a little. That causes a very slight shadow, usually at the top, after a few months.

Posted by Tim Reed (Member # 137) on 02-03-2000, 09:08 PM:

STOP! Do not file your plates, yet! Check the masking limits.

Assuming your pictures started out okay, and since aperture plates don't grow, it is a good idea to make sure the masking stops haven't slipped. Put up some target film and see exactly where you are. This will tell you much.

Good luck!

Posted by Martin Frandsen (Member # 74) on 02-06-2000, 05:03 PM:

I like when the picture 'overlaps' the black masking around the screen just a bit. Are there any SMPTE 'rules' regarding this? in some theaters the picture is WAY in to the black masking and it just dosent look right.

Martin

Posted by John Walsh (Member # 168) on 02-06-2000, 06:14 PM:

Tim's got the right idea: check it first.
There are no SMPTE standards for how much should overlap onto the masking. But, it would be hard to define that. If the aperture is close to the film, you can get a pretty sharp transistion from "white light" to black. If it's far away, you may need to file it out more to insure there is no shadow on the screen. Centurys seem to hold the film away farther than Cinemecannicas, so you need to file Centurys a little more.

Picky people want it as little as possible, but generally will accept about 6" of spill. I personally would allow up to 12" because I had too many screens to keep running, and don't want to come back to places where the bottom masking drooped, or the projector settled, etc. Except for 70mm runs, where I would keep it at 6".

Posted by Tom Kroening (Member # 201) on 02-07-2000, 12:57 AM:

Hey I'm a little confused by a problem im having. We moved a flat format print into one of our booths this week. We havn't had a flat print in there for months (since before i was a projectionist). I changed the lenses and the plates. The image fills the screen on one side and angles inward so on the left side of the screen there is dark space on the top and bottom of the screen. The aperture plate is perfectly straight on the top and bottom, i even swapped it with a plate from another projector and i get the same results. The projector is at angle to the screen which could be causing this. Anyone know how to fix it?

Posted by Tim Reed (Member # 137) on 02-07-2000, 09:11 AM:

Yes, it sounds like you have the wrong aperture plate for that machine. Depending on what kind of projector you have, it *could* be in upside-down; but I don't think you would have the problem you describe, if this were so.

Could it be that it was never filed properly to begin with? Skillful filing (by someone who knows how to file plates) will compensate nicely for the off-angle projection.

Again, before any filing is done, a target film should be used, to determine exactly what the situation is.

Take care!

Posted by John Pytlak (Member # 331) on 02-07-2000, 11:06 AM:

Tom:

Since the projector is at an angle to the screen, I suspect you are seeing a form of geometric distortion known as "keystoning". In effect, one side of the screen is farther from the projector than the other, so it has a slightly larger image. Minor keystone distortion requires bring the masking in to cover the uneven edge. Significant distortion will require moving the projector to be more centered relative to the screen.

A useful tool for calculating lens focal lengths, screen curvature and distortion factors is available from Schneider Optics. It actually simulates the design of a theatre, and graphically shows any distortion due to the design. Check out their "Theatre Design Pro" software at:
http://www.schneideroptics.com/theatre/desprodn.html

Posted by Martin Frandsen (Member # 74) on 02-07-2000, 04:54 PM:

The keystone effect is a big problem in the new 'Monsterplexes' being buildt in my country, and with 'stadium seating' being very popular here the projector has to get even higher up in the ceilling in order to project over the heads of the patrons wacthing the movie. That makes everything even worse. Why not 'tilt' the screen a bit towards the seatings (lowest part of the screen) that can avoid keystoning?

Posted by John Walsh (Member # 168) on 02-07-2000, 06:38 PM:

I worked in a very old theater where the screen was tilted to avoid keystoning. The projectors had a 30 deg tilt. The pedestals wouldn't go as far as was needed, and were bulit up to tilt them more. A real pain to thread- thank god I only worked relief.

A tilted screen still looks weird for the audience, but at least the image is improved. Can't use a gain screen though.

Posted by Tim Reed (Member # 137) on 02-08-2000, 10:22 PM:

Tilting the top of the screen back, to compensate for excessive projection angles, used to be fairly common practice. I remember in the big, older theatres it was really not that noticeable (the tilting). But then, you had all the other fixtures like drapes, proscenium arch, etc.. to draw your eye off the anomaly.

Posted by Richard Hamilton (Member # 321) on 02-08-2000, 10:48 PM:

It is amazing how aperture plates seem to shrink over time!!! In response to the original post:
William, please don't file any of your plates. Please have your tech look at them first. If you have inward bulges on the side, I would guess that the duvatine material has shrunk, and your side masking is no longer straight.

As to Tom Kroening's problem:
Tom, I would guess by what you said that plates have been switched around from one projector to another. You said that you even switched plates with another projector.

My advice is that all aperture plates should be attached to a chain that is bolted to the wall and will only reach the projector that it is filed for. Maybe a deadbolt so that they can't be switched???

My last gripe is to everyone that chimed in and gave advice on filing plates!!! After this thread, going to the movies will be like going to Disneyland where the film plays around you in 360 degrees!!!

Posted by Brad Miller (Member # 2) on 02-08-2000, 11:39 PM:

Richard,

Please remember there are techs who do not file plates out the way they should be for fear of too much spillage. Also, there are plenty of projectionists who are trying to learn. I think the guys here made it pretty clear that this was not something to be taken lightly and he should check with the tech. Still, if he felt it had to be done (many times a manager will give the instruction to do so), at least he's got a few tips and he doesn't go out with a power drill or something crazy.

For Tom's problem, most techs will scratch the number of the projector to the back side of the plate when filing them initially. Tom, you might want to check for this and if not, mark them once you get them all sorted out.

Posted by Randy Stankey (Member # 64) on 02-09-2000, 01:08 AM:

I do have to agree that "working" on aperture plates is a last resort. I guess that I automatically assume that people know that I'm thinking you've checked everything else. (Your masking is okay, etc.)

When our theatre was first opened, we didn't get all the projectors running right until right before opening night. (As usual) Some of the plates were filed rather hastily and there were some 'burrs' on the edges of a couple of them. That's why I recommended using an emery board. It's good enough to get the burrs off but not so aggressive that it'll open up the hole unless you really "have at it". But, again, I assume that the other person has the intelligence to understand things like that.

Maybe, these kind of assumptions are premature?

Posted by Richard Hamilton (Member # 321) on 02-09-2000, 08:14 AM:

Never assume anything!!!
As for the marking of plates, almost all of the theatres that I work on that don't have turrets, have the aperture plates numbered.
Does this help?? In most cases yes, but there are a lot of times when I find both lenses and plates moved around. I had one manager who moved the lens and plate with the print!!! She thought everytime she moved a print that the lens and plate went right along with it. Its really amazing that she didn't ship the lens out with the print. I assumed that this woman had a brain!

Posted by Scott Norwood (Member # 30) on 02-09-2000, 10:03 AM:

All the comments posted here are right on target. I'll add a few others as well:

- Don't cut your existing plates; order new ones ($6 apiece for Centurys; probably a lot more for oddball projectors) and cut those. That way, if you screw something up royally, you can still go back to the old plates.

- Get the proper test films. If you don't have a spare $200 for a roll of RP-40, you can make a loop of SMPTE Universal Leader (the clock-sweep type) and a few feet of film with DTS timecode. The smaller (inner) circle in the countdown defines the 1.85:1 upper and lower borders and the edges of the frame define (roughly) the left and right borders of the 1.85 frame. The loop of film with DTS will help make sure that you don't cut too far on the soundtrack side. The left and right borders of the SMPTE leader are also similar to the L and R borders of the scope frame, although the top and bottom borders are higher and lower for the scope frame (you'll have to cut this by eye, paying attention to splice visibility). The Academy frame (1.33) is the format for the SMPTE leader, so you can pretty much cut to match that entire frame. I don't have a good reference for 1.66:1 top and bottom limits, but you can sort of guess this; you don't have to worry _too_ much about getting 1.66 and 1.33 prints with DTS.

- Allow a lot of time and patience. Aperture plate cutting isn't much fun, but the results can be rewarding. I've cut four sets (all formats, two projectors) of plates using only loops of SMPTE leader and old trailers and existing masking settings. It took about two weekends and wasn't fun at all, but the on-screen image was greatly improved.

Good luck.

Posted by Nick Perry (Member # 361) on 02-26-2000, 01:23 AM:

You recently noticed your plates need to be cut? Were they O.K before? If so breaking out the files is a common mistake. Appeture shadows can caused through a number of minor things that occur over time. Before you file an appeture check a few things,

1) Check your mirror alignment.
It is possible when aligning the mirror to bring it in so far that you get shadows on the side.
2) Check your apperture alignment. Can you alter the alignment settings to fit the screen evenly? E.g it's auto-stop position.
3) Has your projector moved? It will over time particulary if it is a new installation.

These few points should always be checked before you bust out the files.
If you go ahead and file the appeture and it is one of these things you will waste a lot of time and probably end up with a badly over cut apperture which is very anoying.

If it's none of these, good luck!

------------------

Posted by Will Kutler (Member # 770) on 07-05-2001, 02:26 PM:

I came accross this old thread and wanted to add my two cents.

Some of the best files on the market for doing this type of work are Grobet tm. They are not cheap, and should be a standard item in any good lapidary store. This company does produce an assortment of non-tapered safe files. So what does this mean? Non-tapered simply means just that, the file body does not have a taper, and all surfaces are perpendicular. Safe means that one or more surfaces of the file body do not have any cutting teeth. This is perfect when filing 90 degree corners! Another feature of Grobets is that they also produce files that have square-non-radiused corners. Another asset when cutting 90 degree surfaces!

A little about file care and safety:

One of the biggest mistakes that people tend to make when storing files is to throw them together into a drawer unprotected. This is the quickest way to dull and damage files. Always store them in their individual pouches so that they do not rub against each other.

Aperture plates are made of a soft leaded brass that produces fine chips that will easily clog a file. One of the oldest machinist tricks on the books is to pre-load the file with common chalk-board chalk prior to filing. This will prevent the file from becomming clogged. A soft tap on a block of wood, and a few swipes with a good file card will remove the debris. Yes, the file needs to be reloaded with chalk every time it is cleaned. Please note that I did mention to use a file card!

A note about file safety:

Never use a file without some type of protective handle, many serious accidents have happened due to people not having protective handles on files!

Always use protective evewear. Never touch your eyes without washing your hands first! This type of brass produces fine chips that can seriously injure your eyes in a heart-beat!

Remember the motto: Take care of your quality tools, and they will take care of you!

Happy filing!

Posted by Brad Miller (Member # 2) on 07-05-2001, 02:37 PM:

Will's last post:

"I came accross this old thread and wanted to add my two cents."

Then how about sharing your two cents with the rest of us?

Posted by Will Kutler (Member # 770) on 07-05-2001, 02:52 PM:

Sorry Brad!

I was typing as you submitted your reply. My computer gliched and erased my message. I had to fool around with the edit and submit functions. Is there a way to save messages while typing?

Posted by Brad Miller (Member # 2) on 07-05-2001, 02:55 PM:

Yes there are two ways of doing this.

#1 Never press the "submit" button before you finish typing. Your first message said "ravgrgiua". Then you next message was my quote above. This means you had to have pressed the "submit" button at least three times to achieve your post above. The simple answer...just don't press "submit" until you are done. This is not a race, and as such there is no reason to get a post up before anything is typed.

#2 Compose the post in a text editor and then paste it into the reply box via EDIT/PASTE commands.

Posted by System Notices (Member # 2357) on 04-17-2005, 01:46 PM:

It has been 1381 days since the last post.

Posted by Dan Lyons (Member # 1454) on 04-17-2005, 01:46 PM:

BUMP!!

Can anyone recommend a specific brand and MODEL NUMBER of files to buy? I've searched all over, and cannot find any files that don't have teeth on all 4 sides. I've also noticed there are varying degrees of coarseness for files, what coarseness is needed for working on a brass plate?

I see that Nicholson hand files have one safe edge, however they come in different cuts. Which cut would i need?

Posted by Gordon McLeod (Member # 33) on 04-17-2005, 02:26 PM:

Ise the 00258 auger bit file the most and a set of needle files

Posted by Will Kutler (Member # 770) on 04-17-2005, 04:29 PM:

OK Dan

Please read my next to previous entry into this thread!

I specifically answered all your questions! It does pay to read! [Big Grin]

Posted by Dan Lyons (Member # 1454) on 04-17-2005, 04:52 PM:

yeah, i read it before i posted. It doesn't tell me what coarseness or "pattern" of teeth i need...

Posted by Brad Miller (Member # 2) on 04-17-2005, 06:06 PM:

This is what I use

Grobet files

Posted by Will Kutler (Member # 770) on 04-17-2005, 06:09 PM:

Dan

Go to WWW.GROBETUSA.COM.

What you need is under Pillar files. Pillar files are non-tapered and square, so that there will be no corner radius as you are filing. Furthermore, they have what are referred to as "safe files" meaning one or more sides are without teeth. Tooth pattern is not relevant in this case, what is important is tooth coarsness, and Grobet explains this on their web-site.
The best solution for you is to go into a local lapidary supply store. Any decent lapidary supply store should stock a large assortment of Grobet files.

Sears Craftsman has a little life-time warranty Swiss Pattern file set. The tooth coarseness of these files is what you need.

Cheers

K.

Posted by Phil Hill (Member # 371) on 04-17-2005, 06:15 PM:

Brad's link works, Will's doesn't.

But which specific ones do yous recommend? There seems to be a lot of choices for sizes and Pillar types and cuts.

Also, do you "flat-cut" the aperature or file with a slight angle towards the the lamp or the film so as to get a "sharp" edge?

Posted by Brad Miller (Member # 2) on 04-17-2005, 06:34 PM:

I am currently trying to find an online vendor for the set I purchased, but all I seem to be able to find are files sold in singles.

For beginners I recommend filing flat and don't try to get too fancy (unless you have a nice stack of aperture plates to trash). Once you have cut a few hundred plates, you can get crafty by filing at an angle towards the film to make for a sharper plate to produce less projected aperture shadow. (Again that is NOT for someone to do unless they know what the *&$#^%$@! they are doing...because if done incorrectly you could end up putting aperture scratches on every film you run! It also forces you to have more skill because with an angled cut one light pressure slice can take off WAY TOO MUCH and then the plate is useless, because essentially you are working with a newly created thickness that is now maybe 1/4 the normal thickness of the plate.) There are other tricks as well including angling the file a certain way to get perfectly 90 degree corners, how to hold the aperture to produce a curved side to compensate for keystoning and a couple of things that need to be done to smooth out the finished cuts so they do not attract dust that would otherwise cling in the aperture during a show, but again those aren't anything for the beginner to try and tackle.

Don't forget to purchase a nibbler too. It's extra required if you are going to be dealing with Strong equipment since those boneheads can't make a properly undersized plate anymore and you will often have to start from a pinhole. [Roll Eyes]

Kinoton has got the right idea with apertures. They have pre-scribed maximum lines already etched into the plate that serve as a wonderful guide to assist you when using a nibbler! [thumbsup]

Their only problem is that the auto-changer hole is too damn low on the operator's edge of the plate and when removing the aperture the arm likes to jump into one of the actual aperture holes, at which point it falls to the floor. Grrrrrrrrr.

Posted by Gordon McLeod (Member # 33) on 04-17-2005, 06:45 PM:

I always start from a pinhole
and a dremmel tool is a bonus

Posted by Phil Hill (Member # 371) on 04-17-2005, 06:53 PM:

Brad, perhaps the correct way to cut/file plates would make a great "how-to" for the TIPS section...ummm with pics! [thumbsup]

Posted by Brad Miller (Member # 2) on 04-17-2005, 06:54 PM:

Pictures would be useless. The only way to teach is one-on-one or *maybe* with a video.

Posted by Phil Hill (Member # 371) on 04-17-2005, 06:57 PM:

You're right...a video would be cool!

(Where the hell is Joe when ya need him, huh?) [Roll Eyes]

Posted by Brad Miller (Member # 2) on 04-17-2005, 07:03 PM:

While I don't doubt Joe's expertise, I don't think even he could make for an entertaining video on how to cut an aperture. It may be educational, but would definitely be quite boring.

Posted by Scott Norwood (Member # 30) on 04-17-2005, 07:46 PM:

I would _pay_ for a video on cutting plates. This is one of my weak points. I always seem to be able to get either straight edges and sharp corners _or_ correct dimensions, but not both. [Frown]

At least Century plates are cheap.

Posted by Louis Bornwasser (Member # 3063) on 04-17-2005, 08:42 PM:

The files I use are the ones sold by LaVezzi and available from any dealer.

Posted by Monte L Fullmer (Member # 2797) on 04-18-2005, 04:03 AM:

I have a set of X-acto modeling files and a straight, smoothed edge file. Just would like to find some aperture stones to complete my set.

Nice thing about brass: it can be hammered back to fill in the accidental "overcutting" of aperture plates. One theatre had overcut apertures and I hammered that brass towards the inside to be refiled. Took a while, but got it.

Or, one could bronze in a piece of brass with a torch for recutting....seen that done before as well.

Yea P35 aperture plates close to 70 bucks..

-thx Monte

Posted by John Hawkinson (Member # 1135) on 04-18-2005, 09:28 PM:

aperture stones? Do you mean something other than standard polishing stones, like the diemaker's stones midway down page 2493 of the McMaster-Carr catalog?

Also, remember if you have a needle file that isn't safe, you can grind down an edge with a shop grinder, and there you go.

--jhawk

Posted by Will Kutler (Member # 770) on 04-18-2005, 11:16 PM:

India stones are what is being referred to. But a Brillo pad or fine wet and dry sand paper are all you should need to remove burrs.

And ya, burrs, especially on brass is something to look out for. Which reminds me that at my old theatre, which had (and still has) horrendous plates, there was one that looked like a small hair appearing on the screen. Needless to say that it was an unremoved burr that I did manage to cut my finger on [fu]

!

And yes, Christie plates are on the expensive side. CNC machined out of a few dollar piece of brass. My estimate is that it should noty take maybe 2 minutes to completely machine the part, including loading-unloading time. But cost is also determined from several factors including how many are needed per lot and how often, as well as all the associated machining costs.

Cheers

K.

Posted by Monte L Fullmer (Member # 2797) on 04-19-2005, 12:34 AM:

Aperture stones that I'm referring to is a block of abrasive material that is in the true square retangular form-so to fine tune the corners square in the aperture. The material is like of a grinding wheel, but only finer.

Hey, J-hawk,- Thx and yes, it probably be of the same material and shape as shown in the catalog of the post that you presented.

thx-Monte

Posted by Frank Angel (Member # 248) on 04-19-2005, 05:07 AM:

Total black velvet masking covers up a lot of ills [Big Grin]