20' long tube that doesn't droop?

dbaxter

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Premium Member
Got a question this time. Building a screen roll-up - motor at one end, support bearing at the other and 20' of unsupported something between.
I've tried large carpet tubes and got the middle joint of two 10' pieces to be straight enough, but it still droops too much. Also got a couple pieces of PVC pipe and it surprisingly droops more.
Thinking of somehow two wood I beams at right angles to each other, but not sure about how to do that.
We'll be just rolling up 15' of muslin, so it's not particularly heavy when all is said and done.
Thoughts and suggestions welcome.
 
Muffler pipe/tube. Extremely lightweight and non flexible. You will have to create a very good splice in the center, or weld it; it typically comes in 10' sections.
 
Got a question this time. Building a screen roll-up - motor at one end, support bearing at the other and 20' of unsupported something between.
I've tried large carpet tubes and got the middle joint of two 10' pieces to be straight enough, but it still droops too much. Also got a couple pieces of PVC pipe and it surprisingly droops more.
Thinking of somehow two wood I beams at right angles to each other, but not sure about how to do that.
We'll be just rolling up 15' of muslin, so it's not particularly heavy when all is said and done.
Thoughts and suggestions welcome.
@dbaxter Have you considered rolling it up from the bottom such that the entire length of the tube is supported by the fabric when it's fully unwound? Try searching for oleo drops or possibly bottom rollers. People used to roll up canvas awnings this way. I know we've kicked this around in a fairly lengthy thread or two within the past couple of years. The basic concept is the tube is supported by a rope at each end, as the muslin unwinds off the tube, the ropes are rolling up on both ends. When you pull up simultaneously on both ropes, the ropes unwind rotating the tube and winding the muslin back on the tube. In one of the threads one of our regulars, possibly one of the mod's, wrote extensively about how he braced his tube internally with a pair of 1 by's at 90 degrees to reduce bending.
Toodleoo!
Ron Hebbard
 
The internal bracing with 1 by's is how I got the joint strong. Suppose I could buy longer ones to go the whole length, but wanted to ask about other options first.
 
What diameter pvc did you try?

I've always heard large diameter aluminum irrigation pipe which is available up yo 30' does this well.
 
Most roll drop tubes start at 8” diameter and go up from there. General beam engineering states that taller the beam the strong it is. Same applies to tubes. I’d look for something with a big diameter and made from a light material.

Just my 2 cents.
 
I have built a similar motorized roll drop that was over 25' wide with little to no sag. I used aluminum irrigation pipe - 4" min up to 6" - it's very light and has almost zero sag. I used a motor from an awning or shade (tubular motor), and had to make some bushings to make it work. For ours I used 4" pipe that was donated. The theatre I built it for was located in a more rural type area - most of the irrigation pipe comes in longer sections of at least 20' - your issue may be shipping or picking up something that long. In our case the farmer who donated it just dropped it off.

Like you I tried different types of PVC and the strength to weight ratio won't work even with internal stiffeners or even spray foam - if you could find older round aluminum down spout that might work also.

I have seen the irrigation pipe on craigslist for as little as $50 for a 20' section but new may run as much as $4 per foot - still less than $100 and it works perfectly.
 
I'd second Bill's suggestion for irrigation pipe. Light, stiff , requires no additional internal stiffeners, cheap (as anything is nowadays!), and readily available in parts of the country that irrigates things. (Good luck finding any in New England!)
 
Got a question this time. Building a screen roll-up - motor at one end, support bearing at the other and 20' of unsupported something between.
I've tried large carpet tubes and got the middle joint of two 10' pieces to be straight enough, but it still droops too much. Also got a couple pieces of PVC pipe and it surprisingly droops more.
Thinking of somehow two wood I beams at right angles to each other, but not sure about how to do that.
We'll be just rolling up 15' of muslin, so it's not particularly heavy when all is said and done.
Thoughts and suggestions welcome.
I will run a 2x4 down the center of a carpet tube. it is a snug fit and you can put screws along the spine.
you could also rip a 2x4 down to 1"x1.5" and glue, screw this to the full 2x4 making an "X" support in the carpet tube.
The good news carpet tubes are free (or should be)from your local flooring store.
 
Finding a couple straight 20' 2x4s will not be so easy.
You are correct, however I would consider using a 14 ft centered, addind 3 ft on each end. Then running 1" (actual) x 1 1/2" x12' on each side of the 2x4. glue, screw and stagger the joint at the 4' range. Then slide tube over each end. Screw every 12 or 16 inches. (pre-drill).
Adjust these dimentions depending on carpet tubes. Most of them I've used work with 2x4.
 
Sadly, upstate NY does not have much call for large irrigation pipe. Went to several irrigation companies around here and they looked at me like I had two heads when I asked. Our lawns and apple trees get by with smaller stuff.
I did find a straight 16' 2x4 which I extended and sleeved with carpet tubes. Turns out there are two kinds of carpet tubes. One has a spiral wrap construction and the other a continuous wrap. The spiral buckled on me. The drive motor is a 12v motor and right angle gear drive used to pull tarps over the top of dump trucks. 40A power supply and speed controller and works great. I'll put pictures of the set (not showing the screen) up on "Thought we could show pictures ..." forum section.
Thanks everybody for the suggestions.
 

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