[scampy74]

Hello all,

I'm working on building an outdoor movie theater at my house. I have everything pretty well ready, but I'm wondering if I'm going to run into an issue.

I want to attach the screen to a PVC pipe and mount the PVC pipe on the side of my house, directly under a second floor eave. Inside the PVC pipe I have a tubular motor, attached to the bracket housing that will in turn rotate the PVC pipe, which in turn either lowers the projection screen or retracts it and wraps the screen around the pipe for storage.

The screen will be 100"x178", which requires a minimum of 15' of pipe. I currently have two 8' 1-1/12" pieces of PVC schedule 40 with a coupler to join them.

My question is, what level of sag can I expect in this pipe over this span? The screen will weigh about 8.5 pounds total on the pipe, and the pipe will only be able to be supported on the ends.

Unfortunately I don't think I can support the pipe in the middle and still allow it to rotate and wrap the screen around it. Would I be better of using a 10' piece and a 6' piece, to move the joined section slightly off-center?

Anyone have any ideas on the level of sag, and if it's too great of a level, an idea for a different kind of pipe I could use over this distance to minimize the sag? It can't be too heavy of a pipe since it's going to be connected to the side of my house and needs to be 1-1/2" OD (1-3/8" ID) in order to be compatible with my tubular motor.


Thanks!

 

[joecaption]

PVC that long unsupported with nothing hanging on it would sag at that length.
It's also not UV protected and will get brittle over time if left exposed.
I might consider slipping in a piece of EMT tubing inside the pipe to see if that make it stronger.

 

[SPS-1]

If your pipe is 1.38" ID, then you more likely have 1-1/4" schedule 40 pipe.

Its going to easily sag 3 inches in the middle. Going to steel won't help much because of the added weight of the steel. Going to 4" pipe (4.5" OD) will help a little, but for a screen, you probably want zero sag.

Maybe you can put temporary supports under the pipe after unrolling it.

Or else perhaps run it over an edge (or rollers) that is absolutely rigid (as shown below. In the sketch below, the brown support can be as tall as necessary and have as many supports as you want.

(oops - In the sketch I meant to write weight on bottom of "screen", not "roll")

 

[scampy74]

Thank you both for your responses. I've been going around in circles trying to come up with an idea on how to make this work, as I don't have room to make a rigid support in front of the tube.

So far I've come up with this idea:

1. Cut a 1/4"-1/2" channel in a 3" PVC pipe that runs the length of the pipes (as well as a channel in the coupler).
   1. To do this I'm planning on using my circular saw, two 2x6's, and my bench. I will turn the 2x6's on their side (6" standing up) and put the PVC pipe in between them and clamp them. This prohibits the PVC pipe from spinning while cutting, while also allowing me to place my circular saw on top of the 2x6's and slide it along as a guide. By being 3" above the PVC, my saw has no chance of slicing completely through the entire pipe, instead only being able to reach the top of it to cut my channel.
2. Attach 6 corner brackets to top of pipe and back of pipe (3 on each side of coupler), with the screws going into the eave and the wood of the house to provide support to the middle to prevent sagging
3. Slide 1-1/2" PVC pipe with the tubular motor inside of the 3" PVC, with the projection screen slightly hanging out of the pre-cut channel

Then, as the tubular motor rotates the inner PVC pipe, the screen can descend and ascend through the channel unobstructed.


The brackets on the top and back of the 3" PVC will provide structural support, but will not cover the channel to prevent the screen from descending and retracting.




What do you think? Will this idea work, or am I completely missing something that will blow this idea out of the water?

 

[KarenStein]

I solved a similar problem (though on a much smaller scale) by stiffening the PVC with a similar diameter metal rod inside.

For your use, I'd see if there was a size of copper tube or EMT that fit fairly close inside the PVC. I'd prefer copper, because of the smaller outside diameter of the coupling you'll have to use. Extend the metal beyond the ends of the PVC and support that; this will let the PVC spin freely on the support.

Sort of like this:

-)-=====-(-