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Old 07-24-2016, 10:47 AM   #1
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DIY Welded Tube Steel Subfloor

Hi All,

I recently acquired a gutted 1957 Flying Cloud that I thought had a solid floor in it, turns out the PO just screwed 3/4 ply to the old rotten floor.

In searching the forums I found a wealth of awesome information on this topic and have gotten started on fabricating my "forever floor".

My AS had a 5/8 ply floor so I went and picked up 80ft of 5/8 x 5/8 x 16GA(.0625) tube steel to get started. The 5/8 square tubing weighs .5 lbs/ft so I anticipate it will be nice and light. Also the material is only 11.50/20ft so thats a plus.

I am leaving the body and belly skin on.

Plan-
Use the old subfloor as a bending template and double up pieces of 5/8 square around the border of the frame to create a 1 1/4 x 5/8 rectangle for the body C channel to rest on. bracing is tbd.

Still need to figure out-
1. is this a good idea?
2. weld in place OR on bench then install
3. insulating gasket to prevent galvanic corrosion
4. subfloor decking over frame

what do y'all think? Here are some photos of the front section-
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Old 07-24-2016, 10:55 AM   #2
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Interesting. I will keep following.

If I ever do a frame off, I most likely will not use plywood. I might use something like this, though it would be pricey:

http://www.nexaninc.com/products/dec...7DYaAgVF8P8HAQ
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Old 07-24-2016, 11:18 AM   #3
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Thanks!

That material looks very interesting, I assume you'd use the LockDry. Only issue I see is the 1in thickness of the product.

If this doesn't work I will be going with coosa for the replacement as it seems like the best substitute for ply and many members have had a good experience with it. However it is expensive!
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Old 07-25-2016, 12:17 PM   #4
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Made more progress on the front frame section. The measurements are looking to be right on. Each frame section will break on centerline of the trailer cross members and be welded to the frame as well as each other.

I will have the rotted front subfloor out today and will begin the fun task of cleaning out the underbelly.

One question, would you recommend removing the belly skin?

It seems that I should be able to do everything without removing it because of the subfloor frame being welded to the trailer frame. The new subfloor decking will be through bolted from the top to tabs with nuts welded on them on the frame.

Thanks for the help.
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Old 07-25-2016, 01:26 PM   #5
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I wish I had done something like this when I replaced my subfloor. What's your plan for attaching the new subfloor to the inside perimeter of your new perimeter steel framing?
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Old 07-25-2016, 01:58 PM   #6
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That goes back to the perimeter frame idea.

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Old 07-25-2016, 02:05 PM   #7
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Not sure what you are going to do about the elevator bolts and holding down the skin of the airstream? If the new welded frame sits in the c channel you will have to remove and replace the elevator bolts? So I think you need access through both the belly and the interior skins.
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Old 07-25-2016, 03:24 PM   #8
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Quote:
Originally Posted by Aerowood View Post
I wish I had done something like this when I replaced my subfloor. What's your plan for attaching the new subfloor to the inside perimeter of your new perimeter steel framing?
The new subfloor will lay on top of this frame and be fixed to tabs welded onto the frame. The bolts will be countersunk into the ply and there will be nuts welded onto the tabs on the frame. Most likely they will be 1/4in tapered allen head nuts (easy to countersink)
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Old 07-25-2016, 03:33 PM   #9
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Originally Posted by Bill M. View Post
Not sure what you are going to do about the elevator bolts and holding down the skin of the airstream? If the new welded frame sits in the c channel you will have to remove and replace the elevator bolts? So I think you need access through both the belly and the interior skins.
Bill,

I have taken the lower interior skins off and have access to the top of the c channel from the inside, once the old subfloor is removed and the frame is exposed all the bolt holes will be accessible from the top without removing the belly skin. My frame will be installed first and the subfloor bolted to that second from the top down. Therefore I can simply drill holes through my frame where the bolts went through the c channel, OR alternatively I can weld the perimeter frame directly to the trailer then put bolts wherever I want through the c channel. Hope that makes sense.

let me know if i'm missing something here
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Old 07-25-2016, 05:38 PM   #10
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Did you cut 1.25 from the outboard edges of the floorboard before you formed the tubing around it? Otherwise it appears to me that the perimeter frame is going to be to wide. Or is the floorboard you are using as a template the overlay floorboard that you mentioned earlier.

I think I would weld the frame to the outriggers. Make sure that the main frame rails are not twisted to the point where the outriggers sag.
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Old 07-25-2016, 05:59 PM   #11
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Good idea to insulate the steel frame from the aluminum c-channel to prevent corrosion.

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Old 07-25-2016, 08:34 PM   #12
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Aero,
Sorry about the confusion, I used the overlaid 3/4in ply that the previous owner put on top of the subfloor, he/she did a good job of fitting to the interior profile to make the curves.

I will have to make a template for the rear as both layers back there were rotten but that should be easy. I will document how that goes.

You bring up a good point about the frame needing to be square and level before welding it all into place. The area I am working on is not level and I am worried that I may "set" any twist or bend permanently into the framework. A jack and jack stands can only get you so close... If I had a proper shop to do this in I'd just build a new frame from the ground up. I can't believe the "steel" that they used. Any focused loads have the ability to bend any section of that frame. Ridiculous.

That being said, I paid almost nothing for the trailer and don't mind it being off a "little".
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Old 07-25-2016, 08:42 PM   #13
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Made progress on removing the interior and front subfloor. I will treat the rust on the frame and am going to add some bracing for good measure.

We are thinking of incorporating some underfloor storage for beach chairs and other things along the center/middle of the trailer, like a boat water ski locker.
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Old 07-26-2016, 02:08 PM   #14
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This reminds me of a question that pops into my head when we talk about rotten floors etc. What do aircraft manufacturers use for floor boards. Isn't is some kind of sandwich board with aluminum sheet top and bottom? Wonder why Airstream doesn't do something like that to permanently do away with the rotten floor problem and maybe lose some weight in the process.
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Old 07-26-2016, 04:44 PM   #15
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It depends on the aircraft, our C-130 uses built up aluminum floorboards and they contribute to the structure of the airframe and are easy to repair. Our Gulfstream V uses Carbon Fiber and they are structural over the wing center section and have limited repairability and cost a small fortune. Aluminum honeycomb is popular also but again easy to puncture and inserts have to be potted in to attach anything. With Airstream its all about the cost and plywood is cheap. But I do agree with you that there are better alternatives out there other then plywood. Airstream will most likely change the floor materiel when they start to wet seal the seams, which is NEVER.

Sorry about Hijacking your thread Boothy. But Airstreams' process specs, and quality control, or lack of them, gets me riled up
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Old 07-26-2016, 10:07 PM   #16
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Quote:
Originally Posted by Aerowood View Post
It depends on the aircraft, our C-130 uses built up aluminum floorboards and they contribute to the structure of the airframe and are easy to repair. Our Gulfstream V uses Carbon Fiber and they are structural over the wing center section and have limited repairability and cost a small fortune. Aluminum honeycomb is popular also but again easy to puncture and inserts have to be potted in to attach anything. With Airstream its all about the cost and plywood is cheap. But I do agree with you that there are better alternatives out there other then plywood. Airstream will most likely change the floor materiel when they start to wet seal the seams, which is NEVER.

Sorry about Hijacking your thread Boothy. But Airstreams' process specs, and quality control, or lack of them, gets me riled up
Haha no worries! I enjoy all these discussions, and get just as worked up over poor design and build! The majority of the RV industry is pitiful, maybe Airstream needs a few of us on the payroll

Made more progress today, will post an update shortly.
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Old 07-27-2016, 11:18 AM   #17
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Update-
Got the front frame section test fit yesterday, I'll be taping off my weld locations then going to pick up some por-15 to treat the frame with. I removed the loose rust with a wire cup wheel on my grinder and it cleaned up nicely. There was a bit of metal loss due to corrosion on the second to front outriggers where the bolts went through, but its not a deal breaker, the por-15 should take care of it.

To fit the front frame piece without removing the belly pan I had to cut it in half. I planned on that most likely being the case for the front and rear sections so I welded two cross members into place on each side of centerline. It took some coaxing with a rubber mallet to get it in nice and tight but I'm very happy with the result.
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Old 08-22-2016, 10:16 PM   #18
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Looks great!
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Old 08-23-2016, 04:01 PM   #19
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How did you bend the 5/8 x 5/8?

I think that this is a good idea to get the plywood inside the body.
How did you bend the metal to get such a smooth and accurate curve?
How difficult was it?
Did you double it up to get the extra width to match the channel? Would it have been too difficult to bend larger material.
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Old 08-23-2016, 05:43 PM   #20
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Boothy, Perryg114 brings up a good issue. Galvanic corrosion. It's much worse in a marine setting, but must still applies to airstreams somewhat. I don't know if it has been a problem with the long term experience of steel base frames and aluminium skins.
1. Do you plan on any isolation of steel from aluminium? 2. Does anybody know of these issues in a trailer setting , rather than on boats?
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