Welding an exo.

[DirtyMJ]

So, as I see it you have two options (and something inbetween) which would be welding it entirely on the vehicle, or tacking in place and welding it off the vehicle. If you're to weld it off the vehicle I'd think that you would have to design it accordingly in that you'd have to actually be able to take it off - ie, all mount locations would essentially have to be outboard of the body's major dimensions. But if you're to weld it in place care would have to be taken so that the nodes could also be accessed for welding. Which poses more of a problem if one means to keep the cage tight to the body.


Now, I'll go out on a limb and also say that most people would MIG weld their cages, with the exception of those who have the means and desire to TIG their cages.

Am I correct in these assumptions?


Anyways; I'm in need of an exo for my MJ and I'm still weighing my options on execution. I'm limited in space in that my garage only has a 8' ceiling, so if I'm to tack the cage in place and remove it for welding some major creativity would be needed. Hence I would like to weld it in place if at all possible. Which brings me to another limitation - I can't MIG weld. It will be sticked entirely. Which you can actually use to get access to tight places sometimes - but a lot of the time it seems to not help. Also, I do not want my exo to get in the way of my wheeling - ie, if it gets me hung up I'm going to be in a bad mood. Saving sheetmetal isn't really a huge deal at this point - it's really more my life and longevity of the body as a structure.

I appologize for the pics being ugly, and that this is for a MJ but I used my XJ as I have more pictures of it for some reason (WTH?).


My design idea is something like this:

Rear, sides: (old pic, yeah, I fixed that ass end)

The cage behind the cab will not be any wider than it is up into the area where the roof tapers in by the rain gutters. Which means it's not going to help the body much. I figure I'll go with the nice big full X as there's not as much that can be done for lateral stability up front. The bars extending back to the wheelwells might be unneeded - but I will use them as I think it'll look hokey otherwise and I'm going to throw a big 'pane tank there anyways. The sliders are also extended so I can try to squeeze my batteries into that space as a saddle - because that would be cool.



Thankfully my XJ's front end is pretty much the same - other than it sorta has a bumper.

I'm debating if the fender area should go inside the sheetmetal or not. It's not exactly a huge deal if the fenders get messed (wait, they already are) as they can be replaced or flattened if I get in the mood to do bodywork. If they go inside I'm unsure how much protection I will have for the lights at the front. But if I build it as drawn I might as well not have turn signals anyways. And yes, a windshield bar. Do I need it? I'm just thinking I'd better not break the glass if I do it...



Okay, imagine this is a MJ roof:

Obviously this isn't the best design. Another X or a single diagonal cross would be better. But I think it will cause major headaches with the bending and welding if I was to do that. Mostly this would be because the tubes along the sides and front are not above the roofline. Should it matter?


Thoughts, comments, concerns? I'm going to start figuring out how I can build this thing next.

 

[DirtyMJ]

This is how I think I will build it... Other than the front.

The light blue (sliders, and upmounts to the bed) would be welded on first. They're obviously the usual starting point.

Then the main structure would be built in place and tacked up. This includes the roof, windshield bars, and cowl cross bar. I'd then lift the front end of the cage up to tip it off the back of the truck. If this can't be done inside my garage I'll just have to face the cold. It would then be fully welded, then tipped back onto the truck - reverse of removal; and welded in place to the deck and sliders.

The red braces on the rear would then be welded in.


I'd then move to the nasty pickle of a front (light green). I'd be doing it in place. I'll have to decide what I'll be doing with it first though.

 

[Goatman]

It looks like you have it pretty well thought out. Like you said, weld it off the vehicle if possible, but I think most of us welded ours on the vehicle. I welded mine on the vehicle.

Yes, an X on the top would be stronger, and the corners need to be as strong as possible if you want to structure to hold up well on a hard hit. I'd be more concerned about strength and access to weld than I would about how tight you can get the cage to the roof. You'd want an exo tight to the body on the sides, but on the roof it doesn't matter much. And, you should have those rear down bars to add rigidity.

If your B pillar bars are even with the edge of the body line, and you run your A pillar bars down through the top of the fenders, then run tube forward under the fender, you won't have any tubing outside of the body lines on the sides. You can make a front hoop to protect your lights and core support and tie it into the tubing running forward under the fender.

Oh, and if you don't already have one, invest in a good welding blanket.

 

[DirtyMJ]

Advice noted.


One thing that I'll admit I know nada about is gussets. Mostly because I haven't seen any sort of standard formula for their construction and use.

Should I gusset nodes that I deem to be potentially major load carring areas? Should I gusset inside a 90* bend?

What thickness of material should a gusset be? Should it match the tubing wall? How long on each edge of the tube should it extend?


Actually, I think I'll read my airframe manual on the subject. See if it can tell me anything.

 

[DirtyMJ]

Well, my airframe manual had nothing on gussets. Apparently they don't use them. Ah well.



Anyways, I had a wonderously aweful idea. I want my radiator in the back and to narrow to narrow the front anyways... So, how about I bend those sliders up so that I can run my coolant through them? It'll pose a bit of a problem (or maybe a nightmare) at the engine side of things, but I'm thinking it could be done. Of course, if I narrow the front then the whole front tube design is moot anyways - so I could rework it to be better!

So, what size (ID) of tubing would be needed to flow enough coolant easily? Is a high-flow water pump needed for this sort of operation? Is bleeding the system going to be psychotically hard if I retain my closed 4.0 rad? (if it works, dun f' with it)

 

[ponyracer1]

Um you mean the sliders that run right under the door that your legs gonna touch when you get in and out of the truck? Thats gonna suck when that tube is like 180 degrees.

 

[vetteboy]

The rockstomper.com buggy does that to run coolant from the engine to the rear-mounted radiator. If you look in this pic...

...right behind where the bottom of the passenger seat is and just after the bend, you can just make out a hose clamp where it goes from that tube up to the radiator.

I wheeled with it last weekend and felt the tubes, they weren't that hot. Just had to be careful if you leaned yourself on it for too long. 'Course, it was also 15 degrees out, which might have made it a little more bearable.

As far as welding, old license plates can be put behind joints to shield the body from spatter etc.

Here is another option to consider, this guy ran the top of the cage bars right through the corners of the rear window, and then cut a single piece of plexi to fit the whole opening (and around the tubes). His rig worked awesome all weekend.

 

[ashmanjeepxj]

I welded mine on the vehicle, some joints are not full circle. Id rather have it tight to the vehicle and weled to the unibody then far enough to get full welds and be hangingout the sides...

You loose some strength for having a 75% weld circle but when it ties into the unibody that helps spread the load.