building jeep frame

On Mon, 1 Mar 2010 17:52:39 -0500, "Ed Huntress"


Error.. ever see the wings on a B-52? When they taxi out for take-off both outrigger wheels are on the ground; when they come back one outrigger will be ten feet in the air. But not only the wings, a B-52 on the ground has large wrinkles on each side of the fuselage, forward of the wings; flying the fuselage is smooth.
John D. (johnbslocombatgmaildotcom)
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I don't know what the structure of a B-52 looks like, John, but it must be far removed from a true monocoque. If a monocoque's skin wrinkled in compression, all integrity would be gone, and it would completely collapse.
The wings contain spars -- the skin is stressed in tension but takes no compressive loads. That's stressed-skin but not monocoque. Most metal aircraft wings are made like that.
I was referring to the fuselage, of which there are many different designs. As far back as the British Mosquito bomber of WWII, some aircraft have had near-monocoque designs, which depend on the skin (which sometimes is cored sandwiches, as on the Mosquito, and not a single sheet) to handle tensile, compression, and shear loads. As you approach a true monocoque, any stringers and ribs are there to help keep the skin's shape, rather than to directly take out the major loads.
--
Ed Huntress



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On Tue, 2 Mar 2010 02:28:52 -0500, "Ed Huntress"

The only true monocoque airplane structure that I have seen is various light aircraft and even then it is from the rear of the cockpit back to the tail skid. The B-52 forward section is not a pure monocoque as there is substantial structure to built the "two deck" upper and lower areas so there are various formers and bearers but I suspect that the skin does support a substantial amount of the load.
Are you sure that the Mosquito had a "cored" structure? I thought it was cold molded - just layers of veneer glued together.
John D. (johnbslocombatgmaildotcom)
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IIRC, it's wood veneer skins over an end-grain balsa core. It did have bulkheads to maintain the fuselage's shape.
--
Ed Huntress



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On Tue, 2 Mar 2010 09:02:48 -0500, "Ed Huntress"

The "Balsa Bomber"
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John D. wrote:

For what it's worth, I was told that the fuselage skin on a B-52 was unwrinkled until they started flying them at 100ft off the ground at 500mph or something...
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Jim Stewart wrote:

I can't vouch for the flying condition as I haven't seen a flying B52 that close, but the one parked at Boeing in Wichita around 1981-2 matched the John D description nicely, the wings drooped and the sides were puckered in the parked configuration. IIRC the angle of the pucker was mirrored either side of the wing indicating the direction of the stresses in the panels due to the loadings when on the ground.
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wrote:

The B-52 H's that I worked on at Barksdale AFB certainly all had wrinkles and frankly I doubt very much that the average B-52 was ever flown at 500 MPH a hundred feet off the ground as it was deployed by SAC, except for the "iron bomb" aircraft in Vietnam, as a high altitude nuclear weapon delivery system.
In addition the fuel consumption would be astronomical under those conditions as during a normal nuclear loaded mission first refueling was very shortly after take-off, essentially as soon as the aircraft reached cruising altitude, as so much fuel was burned getting off the ground and climbing to altitude that the un-refueled range would be (for a B-52) extremely limited.
John D. (johnbslocombatgmaildotcom)
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wrote:

Aircraft have aluminum monocoque construction. Any plane with a frame has steel (or wood) frame.
Aluminum bicycle frames have a very limited lifespan. The corvette uses a "space frame" which is significantly different in concept, design, and stress, than a Jeep Ladder frame.

Boat trailers are triangular so by basic design see very little flexing.

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I should have read your message before posting. <g>
--
Ed Huntress



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On Feb 28, 6:09pm, snipped-for-privacy@snyder.on.ca wrote:

Not completely true. If one does not exceed 50% of the elastic limit in steel, almost no cumulative stress occurs. From http://www.epi-eng.com/mechanical_engineering_basics/fatigue_in_metals.htm
"It is a simplistic rule of thumb that, for steels having a UTS less than 160,000 psi, the endurance limit for the material will be approximately 45 to 50% of the UTS if the surface of the test specimen is smooth and polished.
That relationship is shown by the line titled "50%". A very small number of special case materials can maintain that approximate 50% relationship above the 160,000 psi level.
However, the EL of most steels begins to fall away from the 50% line above a UTS of about 160,000 psi, as shown by the line titled "Polished"."
Dan
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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 http://www.throttledownkustoms.com/framesCJ7.html http://www.acmejeepparts.com/products/product_search.php?cn=Frames+%26+Accessories&c8 The galvanized versions run around $800 more IIRC
You do not want to use aluminum: flex, fatigue, and strength all work against you.
mark wrote:

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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
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wrote:
*Snip*

*Snip*
Eliminating the arches is gonna hurt come articulation time :(
Plus it's going to complicate the body mounting, the front & rear kick-ups arn't there just for the arches.
As for an aluminuim chassis in general-
http://www.fishing.net.nz/asp_forums/uploads/53972/can-o-worms.gif
Live in an occaiasionally damp area? Aluminum+steel+damp= galvanic corosion = a bitch.
Build your own if you want, lots of people have done it successfully but you'll be a lot happier with the results if you go galvanized steel.
Hit up the Early CJ5 "intermediate " (yes, I know lates aren't intermediates & certainly arn't "earlies" & CJ7's arn't 5's but they're a fairly tolerent bunch) forums-
http://www.earlycj5.com/forums/forumdisplay.php?f 
& do a search on frames, lots of good info from people who have been where you're going.
H..
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mark wrote:

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.
--
Steve W.

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What's that Lassie? You say that mark fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Sun, 28 Feb 2010 06:52:53 -0800 (PST):

you can buy a steel frame for about $2k. Galvanizing add $550. www.quadratec.com
Other options: skid plate front shackle reversal setup integrated rear receiver bumper integrated rear receiver bumper with swing out tire carrier custom motor mounts
--

Dan H.
northshore MA.
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dan wrote:

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.
--
Tim Wescott
Control system and signal processing consulting
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ThemalSprayGuy had written this in response to http://polytechforum.com/metalworking/building-jeep-frame-226620-.htm : 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 www.reneuxit-thermal-spray.com.
Bob The Thermal Spray Guy ------------------------------------- mark wrote:

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How old is your jeep? And after you put a new frame in it, how long will you want to keep it? The thought being that the original frame lasted X years. How long you want to keep it might be less than X years.
Dan
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It is 25 year old now and I want to rebuild it. I have been down the road of sand blasting, metal prep, epoxy paints, polyurethane coatings and as far as I am concerned nothing lasts when the roads are salted in the winter and you live on an island surrounded by salt water. If I am going to rebuild it and pass it down to my kids someday I am going to do it in a way that it will last and not need to be done again. I already have a fiberglass body. I have built aluminum aquaculture cranes, and boats which see much more stress than a jeep frame will ever see. If my original question was if you can build aluminum cranes I can only imagine what the answers would be. As for the torsional flexing, I don't think that exists, sure a frame by itself will flex but when bolted to a body how could it flex and all body seems and lines remain constant. A fiberglass body has no flex and it is bolted to the frame. For the last 10 years my original frame has been so thin you could break through it with a hammer in places and it is still holding up, a 1/4" wall aluminum box frame has to be stronger than that.
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