18' Sunrader roof support

[yestertech]

i added some support for the droopy roof of my Sunrader.  I used aluminum channel, formed into arches, and supported by 5" hunks of 1" diameter fiberglass tubing attached to the hull using Evercoat Kitty Hair, a rlong-strand glass fiber loaded epoxy compound.  I machined some "nut bars" that fit inside the tubes to which the beams attach with 5/16-18 bolts.  Chunks of 1" thick Foamular styorofoam insulation fill the gap bewteen the beam and the inner surface of the roof.I

I don't expect to be tromping around on the roof, but this is a lightweight solution to the droop.  Plenty of space for insulation, lights, whatever.

The beams can be easily removed for adjustments, or the fiberglass work that still needs to be done to fill the vent hole where the bathroom was.

 

 

 

formed beams:

  

 

end support:

 

 

part detail

 

blocking:

Edited July 28, 2023 by yestertech
add an image

[MaineJed]

Very well done, smart idea.

[IdahoDoug]

Well done!  What aluminum beam dimensions, and how did you create such beautiful and even arcs with it?

[yestertech]

I used six-foot lengths of channel 1.25" wide, 0.75" tall, 1/8" thick, purchased from onlinemetals.com.

I contrived a BFD (Bending and Forming Device) to make the bend along the four feet in the middle of the six.  

 

Here it is in all it's glory, screwed down to my fixed wooden workbench in my disgustingly cluttered shop.

 

Note that there is a long chunk of 1" x 1" square steel tube sitting in the channel.  A C-clamp constrains the bending stress to the region between it and the fixed clamp on the left.  The piece under the channel between those two clamps (form block) is where the bending happens when I push down on right end of the steel tube.  I would push down until the channel just touched the end of the curved form block.

Since the bend region is about 4' long, the bend is made in five sections, by re-positioning the channel in the BFD.

 

The clamp at the left has a chunk of aluminum (arrow at upper left) that contacts the base of the channel, not the top of the legs.  The bolts thread into a piece of round bar (arrow at lower right)

 

 

Here's a shot of the channel prior to a bending operation

 

and after

 

 

I wanted a final radius of 110", but had trouble accurately predicting the springback.  I didn't want to bend it too much, since my BFD only works in one direction.  So I had to sneak up on it.  I had to re-make the curved form blocks over which the bend happens four times before I got it close enough to my target, and the radius of the last one was 57".  I suspect that if had been able to bend it to the right radius in one pass, that number would have been different.  I suppose had I bought an extra piece of channel I could have done some experiments to arrive at that number, but I didn't want to spend money on scrap to do so.  In the end my process was at least repeatable across the four beams I made, so the job was done.

 

 

Edited July 29, 2023 by yestertech
clarification

[ToyoGuy]

Hey yestertech,

Wow.

Saw this impressive and thoughtful plan and execution, and looked at your previous contributions here.

Beautiful stuff.

I don't know what you used to do, but they probably didn't pay you enough.

 

The "BFD" acronym inspired multiple alternative phrases to me, all quite useful in a fabrication shop.

 

Keep up the great work!

BR,

TG

[nicklee]

wow，very very nice! 

great arc