My original jeep CJ-7 frame has rusted out and I was thinking of building a new one from aluminum. Would 2 X 4 X 1/4 wall (if that is even available) box tubing have the equivalent strength of the stock
1/8" wall steel frame? I would like aluminum because it will last forever, no need of any paints etc..., very easy to work with and cheaper than building a steel one and having it galvanized. My second choice would be stainless 1/8" box tubing.
This looks familiar, Mark. Didn't you post this same question here three or four years ago? Someone posted something similar.
Anyway, as Joe Gwinn says, aluminum has 1/3 the stiffness of steel, roughly
1/3 the strength for low alloys of each, and weighs 1/3 as much. A box section tube doesn't take advantage of aluminum's low density, so there is no weight advantage in using aluminum in this way. To get equal strength in the same section (2 x 4), the aluminum tube will have to have walls that are
3X as thick as the steel one.
I don't know Jeep frames but if the frame isn't boxed (in other words, if it's a U-channel or top-hat section rather than a rectangular tube), and if you use box-section aluminum to replace it, it will be a great deal stiffer and stronger. But that's because the tube is stiffer and stronger, not because it's aluminum.
All in all, aluminum sounds like it's a lot more trouble than it's worth. Welding that thick section and producing a *strong* weld with it will be no picnic, unless you're an expert. It will cost a lot more for the material. I can't speak for the galvanizing but I thought that hot-dipping a frame was supposed to be a reasonable cost proposition.
During our 8 year tour in the Marshall Islands where you can corrode a glass thermometer, we saw jeeps made of Stainless Steel that were made in the Phillipines. No rust.. People that owned them were not excessively rich. Don't know what they cost, but looking back we should have bought and shipped a couple of them to the US .
You do NOT ewant an aluminum frame. Perhaps stainless steel. Aluminum frames on a jeep WILL flex. Particularly a 2X4 x1/4 tube. ANY time aluminum flexes it is a stress, and all stresses are cumulative. Frame life would likely be measured in months.
Steel is different. It has an elastic limit, and as long as that loimit is not exceeded, no cumulative stress occurs.
I'd build a stainless steel TUBE frame if I was going to the trouble - but Iron Horse (I believe that is still the name of the company) supplies ready made replacement frames at a very reasonable price.
I have the full dimensions for the CJ frames, they have a LOT of bends, brackets, and quirks to make a fabrication job pretty messy. There are several companies that do these from 2x4" tube to replace the double channel original. Under $2000. A quick google came up with
galvanized versions run around $800 more IIRC
You do not want to use alum> My original jeep CJ-7 frame has rusted out and I was thinking of
Roy, as for the bends, I am going to eliminate the arches for the leaf springs, I have a 4" suspension lift so straight frame rails will be fine although I will have to bring them in narrower at the front. Around here we use 4X4 1/4 aluminum box tube to build cranes for aquaculture boats that are constantly lifting 1500+ lbs 8'-10' out from the hydraulic lift cylinder and I see many aluminum boat trailers made form I beam, box tubing should be stronger. Also i have a fiberglass body which is much lighter. Each frame rail will have the load spread out to 4 points due to the leaf springs. Maybe if I use 4 X 4 instead, a 20' length is only ~$200.00
Aluminum is a VERY poor choice for a frame of a Jeep. The frame in them is engineered to flex and allow the suspension to operate well. That flex in aluminum will work harden the frame in a short time and cause failures. The welds will be the first failures and then the rails themselves. Even if you doubled the thickness the frame will be the weak point.
Now if you have access to stainless and a way to work with it that would be a MUCH better choice. It would flex like the steel and retain it's strength. The alloy of the stainless would be a BIG factor though.
Personally if I wanted a long lasting rig I would start with a custom tube frame and a fiberglass or stainless body. One of the locals has a set up like that.
Oh boy, if you can buy a frame that's the way to go. Unless you're just determined to build your own frame for the sake of it, and have a well equipped shop at your disposal, you'll spend less time and probably less money buying one.
Aluminum works differently than steel, and is not corrosion proof -- particularly when you bold a bunch of steel parts to it.
Stainless is hard to weld, and fatigues far more readily than steel.
Steel can be painted or galvanized to not rust, and works pretty darn well for frames. Very few cars have aluminum frames for a very good reason.
That's a decent price. I can only think of three reasons you wouldn't want to jump on it:
1: You just have to build your own frame, for emotional reasons -- I mean, building stuff is _fun_, right?
2: You're long on shop space, tools, and time, but for whatever reason you don't have much cash right now.
3: You're doing something absolutely new and unique, the hottest of hot shit, and that requires a custom frame (see 1). But even there, getting a made-frame for $2k, modifying it, and having it galvanized might be a wiser course.
The way I understand it: Frame flexibility is a compromise between handling and body distortion and reducing the bending stresses on the connections between frame side rails and cross members.
On my Landcruiser, all cross members (except for one) and attachment points are riveted to the frame rails. This allows them to flex w.r.t each other and not build up bending torque. There is a single tubular cross member near the center of the vehicle welded between the side rails that acts as a big torsion bar. It serves to stiffen the legs of the H and return the frame to a flat configuration after twisting forces are removed. The other cross members (being riveted) do not carry bending torque due to frame twist.
This Jeep is not for rock crawling or very uneven ground, 99% of it's life will be on paved roads so there will not be extreme flexing involved. As for buying one, by the time it got to me it on the east coast of Canada, with shipping, exchange rate, tax, galvanizing option, brockerage fees it would be closer to $3000.00.
: Hot dip galvanizing is a process to coat parts with zinc, using chemical baths to clean and activate the surface followed by dipping the part into molten zinc. It works very well and has been around for a long time.
An alternative to hot dip galvanizing is the Thermal Spray process of applying zinc to iron based objects. In the Thermal Spray Process, grit blasting is used to clean and activate the surface for the hot spray process. In addition to cleaning, the grit blast process creates a surface that has multiple 3 dimensional surfaces for the zinc to react and adhere to. This process eliminates all the liquid chemical processes used with the hot dip process. .
After the surface has been grit blasted, a thermal spray torch is used to melt zinc metal, atomize it, and spray it onto the part to be coated. It also works very well and has been used by the US Navy on the fleet for many years.
The cost of the thermal spray system to spray zinc is in the $6000 range. This is a complete system with everything you need to spray the zinc. Obviously, if you are spraying just a few parts, it is more cost effective to take it to a thermal spray job shop or have it hot dip galvanized. Having said that, there is a, ?Tim Allen tool time guy?, in some of us that just has to have a device that you can hold in your hand and spray molten metal!
If you would like to visit a web site for a job shop that sprays zinc, please go to
Bob The Thermal Spray Guy
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Why not aluminum? I have an aluminum boat trailer. Works very well. 3400# boat. The Covette has an aluminum frame as well as the Cadillac bodied Vette. Look at a Corvette and see what they use. Airplanes have aluminum frames. And as long as you design well, the flex should not be a problem.
Ooh -- ouch. Everyone assumes (well, at least I did, and I didn't see qualifications to the contrary) that someone who's posting is local.
OK -- build it yourself. But use mild steel. Unless you're _really_ out in the boonies there should be reachable outfits that do galvanizing. If not, mix up some zinc chromate epoxy primer (if you can still get _that_) and roll it around inside all of the frame rails when you're done with the build up.
Be sure it's square and straight, or your doors will _never_ fit.