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Old 11-25-2016, 08:24 AM   #1
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1972 31' Sovereign
Silverton , Oregon
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Frame crossmember @ plywood splice

We have a 1972 31' sovereign, and At each splice of the plywood floor there is a crossmember that sits 3/4" lower, and on top of that there is a 6" wide strip of plywood that adds support to the plywood edges. I'm moving some crossmembers in my frame to add in a gray tank, so I'm making new crossmembers. I will have them laser cut and formed at work, but I'm wondering that if instead of leaving the splice plate, I just make a crossmember with a 6" wide top flange, I would and another return flange to stiffen that edge, but it seems like my steel crossmember would allow less rocking of the plywood edges. Thoughts and feelings?
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Old 11-25-2016, 08:53 AM   #2
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Sounds like a good solution to me
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Old 11-26-2016, 08:29 PM   #3
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1974 31' Excella 500
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I did something similar - i used 2x5 tube for my custom cut cross member, then i just welded some 1-1/2 inch angle next to it in order to have enough room to secure the floor to the frame. Use teks to secure the floor to the frame, they work great!
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Old 11-26-2016, 08:39 PM   #4
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Thanks
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Old 11-26-2016, 10:03 PM   #5
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I'm trying to think of a reason why the splice plate would be better than steel, and I can't really come up with one other than cost or replicability—though it would also spread out the load and make the plywood less likely to break right at the edge of the steel I suppose.

I think you've got a good idea. Go for it.
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Old 11-27-2016, 07:36 AM   #6
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1974 31' Excella 500
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@thiel I'm with you. I'm fairly certain that was more of a cost saving measure than a practical engineering measure. Using angle butted next to the cross member will provide plenty of room for you to secure two sheets of plywood together.

I suppose one consideration to make would be to make sure you have enough room to secure the belly pan. Thats still light years away from where I'm at though.
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Old 11-27-2016, 08:07 AM   #7
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Perhaps, a two part member results in easier assembly or more flexibility for installing other devices.
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Old 11-27-2016, 08:33 AM   #8
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Possibly, but that didn't seem like the case for my 31 ft excella. It was easier to weld in steel and extend the surface area to secure the plywood floor using the traditional design.

Surprisingly, you'll find that there are much better engineering ideas for your airstream. Several areas of this process have left me scratching my head..
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Old 11-27-2016, 11:54 AM   #9
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I did something similar so both halves of the floor could be bolted to the crossmember. Sometimes I added angle and other times I made a separate outrigger for each section of floor.

Perry
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Old 12-03-2016, 08:09 AM   #10
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I was also planning on lengthening the lower flange a bit, a lot of the rivets for the belly pan are drilled in very close to the web of the channel
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Old 12-03-2016, 09:06 AM   #11
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Yeah, that's the proper way to think about securing the belly pan. There is one area in the aft of my trailer that might require me to weld in an extra piece of angle just to support the belly pan. The existing cross members don't allow for much flexibility.
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Old 12-03-2016, 09:55 AM   #12
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I used 1/4-20 bolts tapped into the frame to support the rear belly skins that I replaced when I did the rear floor on my trailer. The skin was .032 6061-T6 which is thicker and stiffer than the stuff that came on the trailer. I can get back in there when I want/need to as well. I hate drilling rivets.

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Old 12-03-2016, 10:13 AM   #13
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Quote:
Originally Posted by perryg114 View Post
I used 1/4-20 bolts tapped into the frame to support the rear belly skins that I replaced when I did the rear floor on my trailer. The skin was .032 6061-T6 which is thicker and stiffer than the stuff that came on the trailer. I can get back in there when I want/need to as well. I hate drilling rivets.

Perry
That was what I was planning. They make self tapping screws with the rubber seal for metal roofing. My plan was to use those so that I could easily access the rear if needed. I plan on doing something very similar with the tank access. I did eliminate 1 cross member on the rear so I'll need belly material that is a little stiffer.
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Old 12-03-2016, 10:18 AM   #14
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I used those on the side skins to secure them to the frame. You need the extra hard ones or they just ring off even with a pilot hole.

Perry


Quote:
Originally Posted by raphspeaks View Post
That was what I was planning. They make self tapping screws with the rubber seal for metal roofing. My plan was to use those so that I could easily access the rear if needed. I plan on doing something very similar with the tank access. I did eliminate 1 cross member on the rear so I'll need belly material that is a little stiffer.
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Old 12-03-2016, 03:34 PM   #15
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I used the 1/4 self tapping bolt heads too, screwed to cross members
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Old 12-22-2016, 07:49 AM   #16
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Muellar metal or Fastenal can get you tek or stitch screws. Pancake head, not hex head. They will counter sink in the plywood and have a flush head. many sizes. you may need to order them. a #12 1 inch metal screw will go through the wood, top frame. The self tapper takes up less than .25 inch of the 1.0" The threads will penetrate the wood and metal. Use larger than #12 and use less of them. Find a square or torq head and its better than the Phillips head.
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Old 12-22-2016, 09:20 AM   #17
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I've been using these teks. They are solid, coated, and counter sink. A little long, but a non issue for my needs. For me they worked wonders! They're easy to get at Lowe's or any other hardware store, and they're also very reasonably priced.Click image for larger version

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Old 02-25-2017, 07:07 AM   #18
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New Crossmember

Here's the new crossmember, I finally got around to having them cut , and I plan on welding them in later this morning the other parts are for my gray tank mount, and axle lift
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Old 02-25-2017, 10:07 AM   #19
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Originally Posted by Can of beans View Post
Here's the new crossmember, I finally got around to having them cut , and I plan on welding them in later this morning the other parts are for my gray tank mount, and axle lift
Looking good! How much did it run to have those cut?

Looking forward to seeing the progress
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Old 02-27-2017, 08:37 PM   #20
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The pile of parts cut and formed was about $275 there are more parts on that cart than the one shelf.
I made a mistake on my axle lift parts, so I'm going to re-cut them this week, and I think my tank mounting concept is too heavy I'm thinking maybe a couple 2x2 pieces of wood to replace the rail supports, and narrow straps to support the bottom of the tank.
I don't have to put the mounts in yet, so I have time to think about that part. The wide cross members are great though. i would go with 16 ga if I didn't also use them to hold up my gray tank, I replaced the rearmost cross member with a solid one, and I'm going to make a 16 ga wide cross member one to replace the next rearmost, they feel much sturdier with the wide flange. I know the plywood is structural, and I don't plan on changing out all the cross members. I made a bunch of outriggers, because I thought I had some bad ones, but now I'm not sure, maybe if they are left over I can sell them later.
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