Film-Tech Forum ARCHIVE: roll up screen has sags in the middle how can it be fixed?

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Posted by Michael Moore (Member # 3867) on 07-19-2007, 12:33 AM:

I’ve been meaning to ask this question for a while but I keep forgetting to. Our screen is 26 X 26 and is a roll up type screen. That is it is attached on the ends with cables and they are attached to a manual winch, and the whole things rolls up like a window shade.
The problem we have is it has major sags in the middle of the screen! It is horrible, and makes movies look horrible, it is difficult to focus on, and any bright seen shows the wrinkles and sag very well. Our patrons stopped complaining a couple of years back. We have had a rigging crew come in from the Grand Opera House and they could do nothing with it, if anything they made it worse. Has anyone worked with this type of screen before? We have a wooden grid so we can’t fly anything off of it! The thing weighs about 300 lbs when it is all wrapped up close to the grid. We start up film after August 5th and I wanted to correct it as soon as possible, but short of dropping it down and sticking a line on the backing board I don’t see a solution.
[Eek!]

Posted by Steve Guttag (Member # 268) on 07-19-2007, 06:16 AM:

That is part of the life with roll down screens. Better ones are tensioned (on the sides to keep the surface flat) but even though will droop in the middle. The problem is, the material stretches under its own weight and the middle is only supported by the material above it.

Better tensioned ones will have a means for adjusting the tension on the sides to always keep it optimal (just barely any tension...enough to keep the edges from curling).

Other rules for roll down screens is to leave them up whenever they are not in use. The age the most when they are down since that is when the stretching happens.

When it gets bad enough...it is time for a new material.

Steve

Posted by Michael Moore (Member # 3867) on 07-19-2007, 06:59 AM:

well its is now 6 years old, we put I roll it up after every movie plays. When I first came to the theater, the projectionist before me was told my management that the screen needed to be tensioned on the sides with sand bags. The bags were 50 lb bags and stretched the hell out of it. we stopped doing that after I realized what was happening. Who makes these kinds of screens, are very expensive to replace?

Mike

Posted by Stephen Furley (Member # 1277) on 07-19-2007, 07:25 AM:

Are we talking about the type with the roller in a fixed position at the top, or the type where the roller comes down, unrolling the screen above it as it does so. The latter tend to be used for cinema-sized screens. The largest I've used was about 20-25 feet, I'm pretty sure the one on the Concert Hall next door to where I wook is larger, I would guess about 30 feet. The flat screen at the pictureville is a roller, which comes down in front of the Cinerama screen; I'm not sure what size that is, but probably wider than yours. Some rollers are more rigid than others; I've seen some that were terrible. Roller screens are not ideal, but in a multi-purpose venue without the height to fly a screen frame there's not much alternative. The Bradford one looks pretty good, the concert hall one not so good, and the Sheffield Library Theatre one is terrible, but that one is very old, and they no longer normally run film there, just a couple of 16mm shows each year.

If it is badly stretched then you probably will need to replace it. As for who makes them, over here I would say Harkness, over there, I don't know.

Posted by Steven J Hart (Member # 2340) on 07-19-2007, 07:32 AM:

DA-LITE makes the "Scenic Roller". Our theater has one that is 24' wide. It has several small wrinkles in it, but no major sags. Its been in use for 5 years and is rarely rolled up.
Steve

Posted by Dick Vaughan (Member # 540) on 07-19-2007, 07:36 AM:

quote: Stephen Furley
The flat screen at the pictureville is a roller, which comes down in front of the Cinerama screen; I'm not sure what size that is, but probably wider than yours.

It's 33 feet and is a Harkness Denham.

We've had it now for just over 15 years and apart from a few minor wrinkles at the extreme left is just as good as the day it was installed. The box is installed just under the roof steels .
We have movable top masking in the box, the sides are masked by the tabs with a fixed leading edge black strip.

We did install one in the IMAX theatre at the Science Museum which is around 48 feet wide. One of the top people there wanted a flat white screen for lectures and the like.
The box sits on the floor in the screen pit and is lifted in to place by 3 chain hoists to a predetermined height and the screen unrolled.

It has movable top and moving rolller edge masking in box.

It's an impressive beast but it has only been used about 3 times in 7 years!! [Roll Eyes]

Posted by Louis Bornwasser (Member # 3063) on 07-19-2007, 10:38 AM:

Michaei: droops & sags are normal. Every time we sold one, the customer eventually (2 years) was unhappy. We now require a "disclosure statement" that the customer signs acknowledging that "bagginess will happen" before ordering for a job. Louis

Posted by Ken McFall (Member # 845) on 07-19-2007, 05:11 PM:

I have a site that uses a roll up screen that is motorised and cost a samll fortune.

The screen itself has been changed once already but they still have problems with uneven tension acreoss the screen.

One of the things that happeens since the screen was replaced is that when winched up it tends to go side ways and will not pull up into it's housing. The lower roller is not square to the housing so tends to wind side ways as a result.

The owner of the site has complained but nothing has been done about it. The screen itself has streached over time and it is self tensioning in the way the roller at the bottom compensates.

But If I were ever in a position of choosing such a screen I would look else where for another installer. However I do feel that this type of screen is always going to be an ongoing problem as the material ages and stretches.

What makes it worse is that the only way to get to the winch gear is via scaffolding which makes it impractical, and costly, for everyday maintemance.

Side tensioners are the only practical and cheap solution. Not too much tension just enough to pull any curl out. Not what you expect to have to do when you spend many thousands of pounds on a screen but it seems the only way.

Posted by Michael Moore (Member # 3867) on 07-19-2007, 11:15 PM:

our screen (and I will post a pic tomorrow) is of the bottom roller type. The rollers unroll as they drop to the deck. our winch is manual crank so I can make adjustments while I crank up the screen however it goes up uneven greater then half the time. And the roller assay is bending in the middle and this makes it sag even more.

Mike

Posted by Bill Enos (Member # 440) on 07-20-2007, 12:24 PM:

Any chance of installing some grommets and lacing it into a frame and then flying the frame? We did that 5 years ago with our silver screen after wrestling with wrinkles etc. for a long time.

Posted by Michael Moore (Member # 3867) on 07-20-2007, 12:37 PM:

we have a fixed wooden grid, (very old) and hence we have no room to fly anything reasonable in size. We can't even have flying pipes for lights.

Our head space above the pipe line is about 12 feet just about half the height of our screen so this could not work.

We have toyed with the idea of having a fixed screen that is stretched on a frame, putting is behind the cyc, and making the cyc roll up and then push the screen to the front of the stage on a semi flying system.

Might work, but I'm the only tech around! We hire from time to time from the Grand up north to get some work like this done; however we just have a very limited budget, and people in the area are scared to volunteer time.

Mike

[ 07-20-2007, 05:52 PM: Message edited by: Michael Moore ]

Posted by System Notices (Member # 2357) on 08-27-2008, 12:43 PM:

It has been 404 days since the last post.

Posted by Demetris Thoupis (Member # 833) on 08-27-2008, 12:43 PM:

Anyone has any experience with the Harkness Hall Bottom roll screen Denham type? How would one solve the issue with speakers behind the screen. Is there a manufacturer who makes specialiced motorised bases for cinema speakers?
Demetris

Posted by Tony Bandiera Jr (Member # 2365) on 08-27-2008, 01:24 PM:

quote: Louis Bornwasser
<snip>Michaei: droops & sags are normal. Louis

I have to disagree with this. If the screen is properly constructed, it should never sag to any great degree. My facility at UC Irvine has a 28 foot wide(picture area, 31' overall width) Stewart screen that is as good today as it was when the facility opened over 10 years ago. The campus has literally hundreds of roll-up screens of various sizes, (most Stewart or Da-lite) and has NEVER replaced a screen due to sags or droop. Most common reason for replacement is vandalism or tears, followed by motor failures.

Proper operation of the roll-up mechanism is critical, as is the proper installation of the material on the roller in the first place. Any unevenness or positional errors will result in the screen sagging.

quote: Michael Moore
<snip>...the screen needed to be tensioned on the sides with sand bags. The bags were 50 lb bags and stretched the hell out of it. we stopped doing that after I realized what was happening.

Then management and that projectionist were stupid. [Smile]

50 lbs was waaaay too much tension for a screen that size and weight..the material is now permanently ruined. Replacement will be the only sure cure.

And make absolute certain that your roller mechanism rolls up evenly, with no binding. A competent rigger can fix or adjust that.

Screens and material can be had here in the US from Stewart (very high quality but a price to match), Da-Lite, and Harkness (who now has facilities here in the States. Good screens at a very reasonable price.

There may be others but these are the three I know of and can endorse.

EDITED TO ADD:

quote: Demetris Thoupis
Is there a manufacturer who makes specialiced motorised bases for cinema speakers?
Demetris

None that I'm aware of, here in So Cali I have a few clients with motorized lifts for their speakers, they were custom made by parties unknown. A good rigger in your country can surely design a lift for you. [Smile]

Posted by Dick Vaughan (Member # 540) on 08-31-2008, 07:09 AM:

quote: Demetris Thoupis
Anyone has any experience with the Harkness Hall Bottom roll screen Denham type? How would one solve the issue with speakers behind the screen. Is there a manufacturer who makes specialiced motorised bases for cinema speakers?
Demetris

See my earlier post.
We have individual speaker hoists to flyout the 5 screen channels. The sub bass is built in to the Cinerama sound wall so desn't require moving.

There's a good picture of the screen half raised with the speakers on Thomas Hauerslev's In70mm site . Look here

The hoists were also installed by Harkness Hall

Posted by Demetris Thoupis (Member # 833) on 08-31-2008, 07:54 AM:

Thank you for the photo. It does look great

Posted by Richard Fowler (Member # 893) on 08-31-2008, 10:00 AM:

I have a 16 year old 33 foot wide Stewart Ultra Matte tensioned electric screen which has been moved twice (from fire curtain position to a further back flyline). When I speced and sold it I expected some sagging; fortunately with annual side tension adjustment and a bottom masking, there is none in the image.
It cost $25,000.00 when new and has proven to be a good investment, quality wise.

MDI makes a very nice electric roll down...only problem we have is the motor control board being an occasional problem. We are repairing one at the moment and cleaning up a bad install (I speced it but a competitor won the bid).

The worst are the Dalite or (even more worse) Draper manual roll down units....which from your information from your pulley set-up is probably your type of screen....this used to be the cheap screen of choice years ago from cinemas running Rocky Horrow Picture Show.....to protect the main screen....

Posted by Frank Angel (Member # 248) on 09-01-2008, 05:23 PM:

I second Tony -- a well installed roll screen should work they way it's supposed to, and Dick's picture (awesome) shows it -- if they can make a screen THAT size work, then there should be no problem with smaller roll up screens.

We've had two in our smaller theatre; the first install was manual with a bottom roller and ropes and it was pretty ify -- too many variables in terms of rope slippage, perfectly level installation, etc. Then we put in a motorized top roll around 1985 and it has worked flawlessly ever since. Only now a seam has become slightly visible due to its age. There also is a difference in the material of this screen -- it has a black backing making it thicker than the original bottom roll unit. I think this contributes to the fact that we never have any sagging problems. Once the material develops a sag, you're done for. Buy new material. But it also sounds like this screen may not have been installed properly -- true level is essential. It only has to be slightly off "true" and it will not roll up properly. Before I would invest in having new material installed on it, I would have the rig through inspected. The roller itself can have become distorted and that of course will cause sagging.

As for Da-lite screens....they are way too expensive...I mean WAY too expensive, mostly I think because their market normally is education and corporate business, not theatrical. School administrations tend to be a breathtakingly stupid when it comes to spending tax payers' money; many can be sold a bridge in Brooklyn by a good salesman....or as screen that costs 3 times what any theatrical screen company would charge. For a long time you could only get 4:3 from them -- not exactly cinema standard. Only recently have they added screens that are 16:9, and even that a consumer product.