Overlander Camper Frame Material: Aluminium vs Mild Steel vs Stainless Steel?

[Alloy]

Being main load-bearing beams, involved with say a cabover (what's the right term?) then extrusion's better right?

But I am curious as to "splicing", any link to help me visualize how?

There is no best just compromises. Extrusion if your doing skin on frame but you could also form sheet in a way that wouldn't need a frame.

If it is one continous piece then 6061 extrusion is better but once a splice is introduced then 5083 or 5086 sheet plate will have just about the same strength.

I have a weld detail that I'll dig up for splices.

 

[john61ct]

Thanks.

Is there any galvanic issue different alloy joins?

Sometimes seaside, saltwater spray environment

 

[FurthurMore]

Thanks everyone for the further replies.

After reading all your comments, I think I’ve been convinced to change from my original design to the “exoskeleton” frame method with custom home-made composite panels glued on from the inside. There will be less thermal bridging, it will be a bit lighter, I won’t have to deal with as many rivets, and it probably won’t be any more expensive overall. Plus I think it looks more elegant this way.

I will start with a structural skeleton made of 2”x2”x1/8” mild steel angle.



I will then weld on some fully external box section members for the roof solar panels, the rear cargo rack, and to help support the cab-over loft.

Then, 2mm laser cut sheet metal plates will be welded on the outside at the corners and other joints for extra structural bracing. There will also be thicker gusset plates to support the overhang of the loft. The curved shapes on the loft will be made with 1mm sheet metal, unless I can think of a better (i.e. lighter and easier to make) way of doing it.



In mild steel it’s still a bit heavier than I would like, so I will try to optimise it further. Regardless, I’ve calculated that with home-made composite panels I will be able to cut off about 200lbs from my original design.

I’d still like to go with an aluminium frame for the weight benefit (I’d save about 100-150lbs), but I’d probably not be able to weld it well enough, especially when dealing with the sheet metal parts. With mild steel I can MIG weld it all and won’t need specialist cutting equipment.

 

[Alloy]

Thanks.

Is there any galvanic issue different alloy joins?

Sometimes seaside, saltwater spray environment

There's galvanic issues with everything. I've seen the 316 stainless that is 1/2" thick eaten away......but.....95% of the time 6061 combined with 5052 ,5086, 5083 alloys has no issues. The 5% is from adding things to the mix such as silicone, roofing products, copper (Never Seize), galv. steel and graphite....using a pencil on aluminum is a mistake.

You may also run into issues with aluminum fasteners (rivets). These are generally utility alloy so it is better to use stainless.

I've always used a product called T-Gel to prevent corrosion.

 

[Alloy]

Thanks everyone for the further replies.

After reading all your comments, I think I’ve been convinced to change from my original design to the “exoskeleton” frame method with custom home-made composite panels glued on from the inside. There will be less thermal bridging, it will be a bit lighter, I won’t have to deal with as many rivets, and it probably won’t be any more expensive overall. Plus I think it looks more elegant this way.

I will start with a structural skeleton made of 2”x2”x1/8” mild steel angle.
View attachment 640702


I will then weld on some fully external box section members for the roof solar panels, the rear cargo rack, and to help support the cab-over loft.
View attachment 640703
Then, 2mm laser cut sheet metal plates will be welded on the outside at the corners and other joints for extra structural bracing. There will also be thicker gusset plates to support the overhang of the loft. The curved shapes on the loft will be made with 1mm sheet metal, unless I can think of a better (i.e. lighter and easier to make) way of doing it.
View attachment 640704


In mild steel it’s still a bit heavier than I would like, so I will try to optimise it further. Regardless, I’ve calculated that with home-made composite panels I will be able to cut off about 200lbs from my original design.

I’d still like to go with an aluminium frame for the weight benefit (I’d save about 100-150lbs), but I’d probably not be able to weld it well enough, especially when dealing with the sheet metal parts. With mild steel I can MIG weld it all and won’t need specialist cutting equipment.

Looks good

1mm on the front will be a mess once it is welded. Formed sheet with 22.5 degree angles might be better

You may need more verticals the opposite side (from the door) to support roof loads

 

[rruff]

I've always used a product called T-Gel to prevent corrosion.

I think you mean Tef-gel. I've been using it for 15 years to build bicycle wheels; aluminum nipples to stainless spokes. Works great.

And thanks for reminding me to put a layer of fiberglass between carbon and aluminum joints!

 

[Cambruggeman]

I say go with whatever you are most familiar and comfortable with, and openly acknowledge its benefits/downsides so you can work with/around them.

There is no one size fits all.

Personally, I prefer wood. Even though nobody else does.
But when compared to anything metal, it is superior in one way that I could never overlook... thermal performance.
It is simply amazing just how well this camper performs in ANY weather.
And at the end of the day, that is job #1 for a camper. To protect its occupants from weather.

8 years on the road now, and going stronger and looking better than ever

This camper is sweet, and he is right. Go with what you know. There is more than one way to skin this cat. Some of my decisions were due to cost, but most of them are because I know what I know, and I know my limits as well. At the end of the day, no matter how perfect you build it... eventually, something will need repair, so think about that too. What will you use it for, and what is most likely to wear out/fail. Im not a carpenter, and would Never build a wood frame. But the guy above is clearly a carpenter, and his camper has served him almost a decade, and hes still showing it off.

 

[hkky]

These airplane wings that flap like a bird. Amazing the cycle times that are achieved.

Earlier post cite fatigue as a negative for aluminum. This is likely not an issue as the frame can be design to eliminate stress points so that one never exceed the aluminum fatigue stress limit of around 9 ksi, as demonstrated by the aircraft wing. The frame is not under tremendous load and stresses can be managed to be below the fatigue limit.

 

[billiebob]

might be a bit late but between mild steel and stainless steel is high strength steel, HSS, it offers the same strength for a bit less weight and HSS is more resistant to rust, plus more resilient than mild steel or stainless steel.

go to a metal shop, pick up SS, HSS, mild steel, same size, gauge, length, feel the difference then drop them on concrete. pretty sure you'll pick the HSS as the best buy

 

[Peter_n_Margaret]

I flew sailplanes competitively in Australia for 25 years. We would expect about 10X the wing flex of that 767 during a normal flight.
The fatigue limits of aluminium are well known, but if you exceed them, it will break. The fatigue limits of composites are almost infinte, by camparison (and so is wood).
Cheers,
Peter
OKA196 motorhome

 

[jwiereng]

W

That is a different case. A composite camper does not require any external strengthening. Our truck carried 500 lbs of spare leaf springs on the roof for 23 years on a steel roof rack that was only supported by the box corners. One of the first things I removed. All that weight up high is crazy.

why did you carry leaf springs on roof rack for 2 decades? Did you forget they were there?

 

[jwiereng]

W

why did you carry leaf springs on roof rack for 2 decades? Did you forget they were there?

Or was that before you bought the truck?

 

[Joe917]

1st owner put them there, they were the first thing I removed.