building jeep frame

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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.

Re: building jeep frame



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I don't think a frame made of that tiny tubing would be very good.

Steve <g>



Re: building jeep frame


mattathayde had written this in response to
http://rittercnc.com/metalworking/building-jeep-frame-226620-.htm  :


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mark wrote:




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http://www.pirate4x4.com/forum/ is going to be your best resource for this
info,
these guys do very crazy builds.

i dont know my al and steels very well but i think AL might have issues
with the
welds stressing and with temper changing over time

-matt


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Re: building jeep frame



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Aluminum is far less stiff than steel, and doubling thickness may yield a
too-floppy frame.  I would stick with steel unless you reengineer the frame.

Joe Gwinn

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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.

I'm sure you'll get other opinions.

--
Ed Huntress



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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 .

Stu Fields



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wrote:

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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.

Re: building jeep frame


snipped-for-privacy@snyder.on.ca wrote:
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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.

--
Tim Wescott
Control system and signal processing consulting
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Re: building jeep frame


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.
 
--
Paul Hovnanian     mailto: snipped-for-privacy@Hovnanian.com
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Re: building jeep frame


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Why is a riveted joint more flexible?

jsw

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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.

Re: building jeep frame


mark wrote:
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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.

--
Tim Wescott
Control system and signal processing consulting
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Re: building jeep frame


Tim Wescott wrote:
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If box section then you need to provide drain holes for the zinc to
enter and exit. A guy I knew had a box section chassis galvanised and
the company didn't drain it well, they charged by weight so he got a
bigger bill than originally estimated and couldn't carry the chassis
easily any more. So get a fixed price or make sure it can be drained
easily. A company near me gets Marcos chassis galvanised, talking to the
owner he said it took them a few goes and a tame galvaniser to get the
drain procedure right but the Marcos chassis is somewhat more
complicated than a ladder frame Jeep chassis.

Re: building jeep frame


Jim Wilkins wrote:

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Probably because a rivet (like a bolt) doesn't support torque loads along
its axis. So the joints can be made more flexible.


--
Paul Hovnanian   snipped-for-privacy@hovnanian.com
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wrote:


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Setting aside the question of whether SS is a good choice for the OP's
project, the common austenitic stainless steels -- 304 and 316 -- are
among the easiest materials to weld. The fatigue limit of both alloys
is in the 35 to 40 ksi range, higher than the fatigue limit for common
structural steels.

--
Ned Simmons

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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.



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Boat trailers are rarely twisted the way that off-road vehicles routinely
are.

The same thing applies to Corvettes.

After all, when was the last time that you went rock-crawling with your
'Vette? <Grin>

How about mud-bogging or bouncing around on deeply-rutted roads?

Jeeps are expected to do all of these and more without any ill effects.
(Getting dirty/muddy is, for a Jeep, a good thing!)

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Hell, I raced a vette, steel chassis, and it got to rock clrawing a couple
times.  :>)  And boat trailers are regularly towed over uneven ground.



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With only 1 wheel in contact with the ground while the boat was loaded and
tied down and the tow vehicle at tilted in the opposite direction?

I doubt it.

"Uneven" is a long way from "rock crawling" and your 3,400# boat is
unlikely to be towed over "Jeep" roads on an all-Aluminum trailer with any
regularity.


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With three points taking out the loads -- hitch and suspension supports,
which generally are paired but close -- there is no significant torsional
load on a boat trailer. It's all simple bending. You can deal with that, but
if you towed your boat 100% of the time, I think you'd develop fatigue
problems in aluminum.

The aluminum Corvette chassis are semi-space-frame with some shear panels.
The subframes resolve their loads in three dimensions. There isn't much
flexing there.

The same applies to aircraft, which often are near-monocoque. If they flex,
you die.

--
Ed Huntress



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