Film-Tech Forum ARCHIVE: Cutting aperture plates

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Posted by Ron Curran (Member # 3631) on 03-03-2006, 10:50 PM:

What is the easiest way to cut aperture plates? I have to cut a new plate (flat/scope slider) because, on some prints, the edge of the DTS time code is visible on the masking in scope. Oh for the days when they were separate plates. I used to think that the easiest way was to get another projectionist to do it. Could somebody invent an adjustable plate system with electronic presets? I would like it before next Thursday.

Posted by Dominic Espinosa (Member # 2122) on 03-04-2006, 03:02 AM:

First be sure your latteral alignment isn't off.
As for cutting them there's a few topics on here relating to it. It's mostly a matter of preference. Some prefer a nibler for the whole job others a nibler and file combo, etc.

I suggest the search function.

Posted by Mark Gulbrandsen (Member # 72) on 03-04-2006, 09:58 AM:

Ya have to use BOTH a nibbler and a file since the nibbler doesn't leave a continous smooth edge. You also need a file without serrations on the edge so you don't over cut in the corners. LaVezzi and a few others make the correct files for the job.

Mark

Posted by Louis Bornwasser (Member # 3063) on 03-04-2006, 11:11 AM:

Might be able to file the OUTSIDE of the plate making it go further into the projector. Only works if the other side has some metal left. Louis

Posted by Steve Scott (Member # 630) on 03-04-2006, 07:43 PM:

And when testing out each plate as it is filed, make sure that no more than 6 inches of image spills onto the edge masking of the screen. This will ensure that no shadows are cast on the edges.

Posted by Monte L Fullmer (Member # 2797) on 03-05-2006, 02:51 AM:

...another trick, if the overcut isn't too big, is to take the aperture plate, which is usually made of brass, place it on an anvil, or hard piece of flat steel.

Since the soundtrack side of the aperture opening is towards the outboard end of the plate, one can actually "move" the brass from the outboard of the opening toward the inside with light taps with a small round end punch and hammer.

Also, as one lightly hammers, the punch is positioned in an inward angle towards the center. By doing this, the punch is actually "pushing" the brass inwards to where there is enough "pushed" brass to do a refile on that one side.

Had to do this a few times on overcuts that I've noticed.

Saves on the extensive filing and purchases of a new aperture plate.

...Course, having a Dremel tool works wonders on cutting new plates as well with the right grinding bits - then just file for the fine and straight edge...lol.

EDIT: before you do begin to cut any aperture plate(s), make sure that the projector/console is level - both "X" and "Y" areas since a lot of units will settle over time.

After making sure that your units are level, then run a "RP-40" loop to ensure the machinery is level and center with the screen. How you do this is with the flat lens in the machine, the loop running and the aperture plate removed.

Then, before cutting apertures for the anamorphic lens, continue running the "RP-40" to ensure that the lens attachment(s) are centered with the projector after leveling the console/projector to square. And if the anamorphic attachments are in a turret setup, use the adjustments needed for centering that lens to the projector. Even with single lens machines, some machines do have a fine tuning to center lens with the machine.

And, if no fine tuning adjustments to center the lens with the machine, is to, once again have the "RP-40" loop running, flat lens, aperture removed and physically moved the base of the console/pedestal to center the machine to where the center line of the loop matches the center line of the screen. Then, once again check for the "X"/"Y" leveling of the unit after such a move has been taken.

-Monte

[ 03-05-2006, 11:50 PM: Message edited by: Monte L Fullmer ]

Posted by Will Kutler (Member # 770) on 03-06-2006, 02:05 AM:

We beat this topic to death long ago.

The type of file that is needed can be purchased through Grobet... the premier file manufacturer that can be found at any reliable lapidary supply store.

Look at their on-line catalog, but what you need is a non-tapered "safe" file meaning that the entire length of the file has no taper, and one or more edges have no teeth.

Grobet has a variety of safe file sizes, ranging anywhere from Swiss to larger files and with a full variety of tooth coarsness (mill, fine, bastard, etc, etc)

And since aperture plates are generally brass, here is a very old Tool and Die Maker's trick to prevent a file from being ruined from "clogging" due to brass being a soft metal: Loading the file with chalkboard chalk and cleaning it with a file card every few strokes as needed and then re-loading it.

Also, file safety...ALWAYS use a file handle and safety glasses! That brass leaves "fine" chips that can easily get transfered from your fingers to your eyes, if you happen to touch your eyes while filing! That fine filing chips can also damage projector and film if it is not carefully cleaned up!

Also, be sure to deburr aperture plates after filing. I know of one "tech" who failed to do so, and I became this idiot's victim. Anyhow, during one show, it appeared that some type of hair or bristle brush was cought in the aperture and was annoying on screen. Anyhow, it was not a hair of brush bristle, but a filing burr that cut me like a razor blade when I went to inspect it!

Posted by John Pytlak (Member # 331) on 03-06-2006, 03:05 PM:

ALWAYS check to be sure the projected image area complies with standard SMPTE 195 by using the SMPTE 35-PA (RP 40) Projector Alignment Film.

Posted by Richard Fowler (Member # 893) on 03-06-2006, 05:36 PM:

Yes use 35PA to verify ratios,projection steadyness, centering and squaring up.....filing plates to it you may find yourself slightly oversized when projecting normal film. I like to use 35PA, Schneider CLT and a test reel [Cool]

Posted by Tristan Lane (Member # 1169) on 03-06-2006, 08:45 PM:

The Lavezzi aperture file is in fact a Grobet swiss file.
The part number is AF-13.

Posted by Monte L Fullmer (Member # 2797) on 03-06-2006, 10:49 PM:

I got two of those Swiss made Lavezzi AF-13 files. Might be a bit on the pricey side but they are the best to use.

[ 03-07-2006, 01:10 AM: Message edited by: Monte L Fullmer ]

Posted by Gordon McLeod (Member # 33) on 03-07-2006, 01:27 AM:

I use the nicholoson augur bit file a set of needle files and a dremel tool

Posted by Lindsay Morris (Member # 1430) on 03-07-2006, 04:03 AM:

Ron,

If you do not want to go to the trouble of cutting a new plate you could do as I have done in the past on my previous Simplex Standards to simply build up the offending edges with silver solder.
Both of the machines I used to use had a range of aperture plates with them when I acquired them but were nowhere near the correct sizes for modern prints. If you are familiar with Simplex you will know that they had a strange but effective aperture plate system where the plate itself was actually "locked" in place with a "keeper" plate. The actual aperture plate was pressed out of brass and unless you had access to that special press making a new one was a bit of a task...If it could be done at all... never seen a good one done without that press though [thumbsup]

I found some Silver Solder which can be worked with a normal soldering iron and was quite stable in the heat of the carbon arc lamps I was using.
I simply built up the oversize bits layer by layer and when I had enough built up carefully filed it to the required shape using a fine file with a "dead" edge or no teeth on one side which are readily available in Engineering supply shops in OZ.
As to the solder it is a CIG product on a card just called High Strength Silver Solder Kit and quite often available in the bigger hardware stores in OZ. CIG now is BOC Gases so maybe a call to their welding section in Sydney might help track it down.
I did all 6 apertures at Kookaburra and although the solder is certainly softer than the original brass never had a problem with it changing it's shape and I covered up some pretty big holes in those old apertures.
I also did 2 for a mate who had a DI at a country location also Simplex and also running carbon arcs at 80 amps so quite hot little gates and no problems at all.
You just have to be very careful that you use a fine file for the final cuts and taper the edges back from the film plane to a nice sharp clean edge at the backside of the plate.
I will probably have to attack my Century CC this coming summer in the same way IF I can find another shorter focal length scope backing lens as I have some DTS on screen at times in scope. I will bring both sides in and leave the top and bottom alone as there is a bit of unused screen top and bottom on scope. Maybe that will take the neg flashes I sometimes get go up onto the top and bottom masking [Smile]

Lindsay

Posted by Will Kutler (Member # 770) on 03-08-2006, 05:51 PM:

Hi Lindsay

While you do have a good idea with silver solder, your method is by far more expensive than purchasing new early Simplex plates...they are usually dirt cheap.

Now, what is extremely expensive is Christie plates!

Kutler

Posted by Lindsay Morris (Member # 1430) on 03-09-2006, 01:37 AM:

Will,

That Silver Solder is still available here in OZ at $9 a card which is more than enough to do about 50 aperture plates.
Only cost is some time with a nice hot soldering iron and some nice clean edges that you wish to build up.
Then it is just a matter of running a couple of beads of solder on top of each other until the desired build up is there and then set out with the file. Dead easy [thumbsup]

When I was hunting the Simplex plates I did not know this site existed and certainly nobody I knew in WA had any s/h Simplex Standard plates which are a strange but effective design being pressed into shape. I thought I almost had got my hands on the special press that was used to make them but the guy who "thought" he had one could not locate it.
In fact a couple of the "old hands" in the cinema game in Perth gave me a real hard time about installing "That old crap" as they termed it but as it turned out I got 7 summer seasons out of the old girls and only switched to a single Century because of the cyan tracks. Even now they still turn over easily having lain idle for 3 years just covered up... were very reliable and certainly better than some of the gear the old hands had foisted onto other unsuspecting exhibitors.
With the number of nights I run I often think now that changeovers would have been the better way to stay as there is a lot less make up time. Particularly when on the final session I used split reels taking up directly onto cores [Smile]

Down side is that not many "projectionists" now want to get to know about carbon arcs plus their foibles and many do not like getting their hands dirty now:D
Thus if you just want to hide a bit of DTS or cover up a file "nick" a wee bit of that silver solder works miracles.
Lindsay

Posted by Ron Curran (Member # 3631) on 03-09-2006, 02:30 AM:

Thanks everyone for ideas. (how many projectionists does it take to change an aperture?)Actually we used the silver solder trick some years ago on the 1:85 side but we thought it was cheating. After 1000s of hours without problems it is good to hear that other projectionists give it the silver seal of approval. The score side is now clean with a sliver of silver.