Steel vs Aluminum tubing (Camper frame)

[montaillou]

So, I'm about a third the way through my 30 point "checklist of fun" and I'm thinking about item 20, the camper.

Is there anyone here that knows more than the average person about structural tubing, aluminum vs steel vs ?? that I can pick their brain with a few questions? I'm also wondering if I should consult a profession for $$, but it's such a small job that I don't know that I could get a pro to take an interest w/out ponying up a lot of $.

I've found some calculators on line for tubing.

Essentially, I need to span the length of the interior of the bed (87") suitable for holding 500 lbs, with little give. The reason for the 500 lbs (and there is wiggle room in this figure), I want to suspend a double-sized bed in a custom frame (& 2 occupants) from the cross beams that would then swing up to nestle against the ceiling. Also, I could see having guests on the roof, walking around.

The floor also needs strength. I plan on having a custom (90g) fuel tank built that would sit below the floor (between floor & bed) and it's probably cheaper to reinforce the floor to bear weight than to have the tank bear any. I will also have a clean water tank & grey water tank in this space between the floor & bed. I don't plan on having any parties inside this thing, so the floor would only need to support 1-2 people moving around.

If I use steel, I may weld it myself (100 hours welding classes in steel). I don't feel confident welding aluminum and would probably hire a pro driving the costs way up, I may hire a pro either way as it's a relatively small job and if I design it right and buy and cut the material myself I can save that way.

I suspect the frame will signify one of the heaviest portions of this camper build. It's such a small project that I don't know that I would realize a significant savings in weight by going with aluminum. While Al is considerably lighter than steel, it's not as strong and increasing the size of the Al also contributes to a corresponding increase in $, and it's more expensive to begin with.

Right now I'm thinking something in the realm of 2" tubing. I don't want too big a tube because space is an issue, but I will also line the walls between studs with sound insulation. I'm not too worried about R value as any heater I use will be overkill + blankets.

There is more that I've thought of, but this is the general idea and this post is already pretty long.

Oh, right wind shear...it's going to be on a vehicle with a top speed of 62mph. but I could also see this thing being parked in coastal places and experiencing 100mph (+?) wind gusts. I am planning on using a wall cladding that's used on office buildings.

 

[davidb56]

steel is 3x stronger than aluminum pound for pound, so its a lot cheaper in cost for the same strength required.....use steel. BTW steel rusts and can be easily repaired. Aluminum corrodes and is difficult to repair. I was a welder (aluminum)on the St Frances Challenge built at Stephens Bros in the 80's. Platform Gail off shore oil rig (Santa Barbara coast) (steel) too. Welders have "hot" tempers and drag up a lot....fancy term for quit. Want to see the reverse flow smoker I built a couple years ago? its huge.

 

[rustystud]

steel is 3x stronger than aluminum pound for pound, so its a lot cheaper in cost for the same strength required.....use steel. BTW steel rusts and can be easily repaired. Aluminum corrodes and is difficult to repair. I was a welder (aluminum)on the St Frances Challenge built at Stephens Bros in the 80's. Platform Gail off shore oil rig (Santa Barbara coast) (steel) too. Welders have "hot" tempers and drag up a lot....fancy term for quit. Want to see the reverse flow smoker I built a couple years ago? its huge.

Hey David. I didn't know you where a welder to ! Looks like we have quite a bit in common. I welded Steel, Aluminum, Cast Iron, and a little bit of Brass when I worked at "Kolstrand Marine" in Ballard . Oh the days of the "endless bead" !!!

Another thing to consider is the "flexibility" or lack there of in Aluminum. Steel will bend quite a bit, then spring back. Or it can be bent back easily, while Aluminum will just break/snap . Depending on the type of Aluminum of course.
Remember back in the 1980's truck manufactures played with Aluminum frames. They found out pretty fast that even the "special" aluminums will only bend so much before breaking. I know there are still a few out there playing with Aluminum, but most went back to steel.

 

[WillWagner]

There are other options for a top bunk, try looking at toy hauler set ups. I have a Carson Trailer ands it uses a pull down bunk that when up, allows a person to stand under it and pulls down 3 feet or so. It is suspended from the walls with spring loaded "hinges" if you will. My sons trailer uses a system that has 4 of the gas struts like a car hood or hatch back and there are also some that utilize what looks like the rail EMT is suspended from, but heavy duty. Both of those also support from the walls. I'll see if I can get a pic of mine today, the trailer is loaded so I can't show the bunk down.

 

[WillWagner]

here is a pic of theCasson bunk in the up position, see the black boxes on the wall? those are the hinges.

 

[davidb56]

Also, if you decide to use aluminum, which I wouldn't, you had better TIG weld it all. When MIG welding aluminum, you get a "cold start" where there is little penetration of the weld, and thats usually where a weld will eventually crack and fail. steel to a far lesser extent. Too many variables to weld aluminum and a fab shop will kill $$$ you if you specify TIG welding only.

 

[montaillou]

Also, if you decide to use aluminum,...

For half the weight, 3x the price and 3x the deflection I could go with aluminum. So, I would probably save around 500 lbs. Steel tubing will cost around $2k.

I am figuring in a max weight of 3500 lbs in the bed, I don't think I'll need that 500lbs as much as I need that $4k. I'll almost certainly be going with steel.

The column pieces don't need to be anywhere near the thickness of the roof/floor pieces. 20 gauge (about 1mm) steel 1 x 2 buckles at 3k lbs.

I'm not sure about welding 7 gauge tube to 20 gauge (or even 16 gauge, 1.5mm, twice the load), maybe I should use connectors?

 

[davidb56]

Borrow or buy a lincoln sp100 weld pac wire feed welder. you can run flux core wire with it outside and don't have to worry about the wind blowing the shielding gas away. its 120vac input and cost under 400$ new. it will weld 20gauge (move quick) and up to 1/4 inch plate. Just keep the duty cycle down with the 1/4 inch. Ive had mine now for over 20 years. I also have a Hobart 140 wire welder for heavier stuff. Its 120vac too. Id stay away from the 240vac ones because you loose the "portable" capabilities. If you need bigger....go a lot bigger and gas/diesel like a old SA200 pipeline welder. I love mine, except when its raining.

 

[montaillou]

I have about 10 hours with wire feed, and about 100 hours with stick. I have an Amico Tig-225 which I bought to stick weld small stuff, weighs about 25 lbs, very portable, and a Miller Dialarc which weighs 505 lbs and is not very portable. I don't have a good place for the dialarc so it's not usable atm - another project.

I was gonna buy a couple tubes and practice.

 

[davidb56]

10 hours with a wire feed is plenty when you use a flux core wire. if you are good at brazing, the TIG would be easy to learn, but you still need a TIG torch, preferably a foot pedal, and possibly a coolant tank and pump if you are going to exceed the duty cycle on the air cooled TIG torch. Unless when you said "to stick weld small stuff", you mean TIG, and its already set up that way. My SA200 arc welder has TIG capabilities, if I buy the accessories. when you are starting out welding, you can use soap stone, or sliver line pencil to mark where your welds are to be(it won't cause porosity), so you dont "wander" all over the place laying a bead where there is no joint. Keep your lens clean, and if it fogs up, stop. A grinder is your friend.

 

[Another Ahab]

Late in, but good stuff here:

- Subscribed

 

[Another Ahab]

Welders have "hot" tempers and drag up a lot....fancy term for quit. Want to see the reverse flow smoker I built a couple years ago? its huge.

Nice smoker. How's the airflow "reverse"?

 

[davidb56]

heat/smoke from the fire box flows under the divider pan, which has a slight slope and "V" for drainage, to the opposite end then up across the food racks. It heats the divider pan, then has to flow completely across the food to the exhaust stack, then out. this makes sure there is no short circuits and "even" cooking. It also makes the temperature easier to control.

 

[davidb56]

here is the diverter pan with the fire box exhaust open on this end and the far end too. it has to flow across to get out the stack which will be on the top of this end.

 

[davidb56]

the fire box has a bottom air supply to feed the fire, and a top one to help it draft into the lower part of the smoker.

 

[davidb56]

Is this breaking some rules going off topic? I get carried away when its about building stuff.

 

[Another Ahab]

Is this breaking some rules going off topic? I get carried away when its about building stuff.

Yeah, we need to back off, but that smoker is very cool!

My apologies, montaillou, we got carried away.

Better lay low, you and me, before we have to do time...

 

[montaillou]

Unless when you said "to stick weld small stuff", you mean TIG, ...

I mean SMAW. My ~100 hours was at the local tech school, night classes.

 

[davidb56]

I mean SMAW. My ~100 hours was at the local tech school, night classes.

then go with the wire welding. 16 gauge is pretty thin and you'll blow through it often, then have to close the gap. Id use the wire feeder if I was doing it. I only use stick (SMAW) with heavier steel ( 1/4 inch above) or alloy applications.

 

[montaillou]

Alright, picked up a Lincoln "Handy" welder, wire feeder.

Right now, my thought is something along the lines of 7 gauge 2x2 for the roof/ceiling (87") and the same for the floor. The roof pieces will be spaced 24" (or 18"?) OC and rest on probably 18 gauge 2x2 for the side frame. On the roof, I will have 18 gauge 1x2 at 29" and 58" welded perpendicular to the 7 gauge to help with stability/rigidity so the space between the rafters don't bow much. I'll probably have the 1x2's in the walls, but I think maybe 1 line of these would be enough. There will be a "crawl space", about 9" high, which will contain a third fuel tank, grey and fresh water tanks, plus extra storage - maybe some of the ammo cans for the battery (see below). I expect the truck will be around 11' maybe a few inches past that when I'm done, still a bit below semis which are 13'

There will be a rather sturdy door on the tailgate side, and a roll-up door on the cab side. No windows, but skylights. I'm also thinking if I can make it so one wall section on each side (driver/passenger) moves straight up inside a frame to create a cross breeze when parked. The exterior skin is 1/4" faced with aluminum on each side with a core of plywood.

There will be a wood burning stove (made for boats), tankless water heater, electric toilet, probably 1 burner stove, an oven (haven't researched this yet), water purification system, HVAC...the floorplan isn't set yet, still building a list of what I'm gonna put in it. Anything that needs power will be electric, drawn from the 12v or powerwall.

I've started doing my research on building a 10kw powerwall that I'll mount (preliminarily) in ammo cans that I'll mount under the bed. I just ordered 3 - 30 cal ammo cans, which I think might work. The batteries (18650's probably) will have foam around them inside each can and each can will be wired together to form the battery. I'd like to hook my 12v alternator to this battery as well as install 2 solar panels and a windmill on the roof. It'll take somewhere around 750-1100 batteries for 10kw. Might be a few cans.