Cage gussetts

[idickers]

I'd like to make some gussetts for a roll cage made of 1.5" x .095 DOM. The door bars will be crossed in an X-pattern like the attached photos, and I'm trying to figure out what thickness sheet metal I should use? 18 ga? 16 ga?
Thanks for any suggestions,
Ian

[JaysinSpaceman]

I hope this is OK with the Moderators, if not I will delete it.

If you follow the link in my signature for the 4x4 gussets I would be happy to supply you with some of the gussets I make from 10g cold rolled.

Otherwise, If you want to make them yourself I would do it out of a minimum of 16g.

Jaysin

[Izzy]

10g! Holy crap! Way overkill for sportscars, but probably just right for 4x's

I usually try for 14-16g

Make your pattern out of 20g as you have a pretty complex shape that your wrapping.

[IZwack]

School me: why does there even need to be a gusset at that intersection? The plane at which the gusset are intended to aid in is perpendicular from the force (side impact).

[idickers]

Thanks for the comments. This is for a 2000 lb road race car, so 10 ga is a probably a little heavy. For comparison, I have a couple of saddle gussets designed for this type of tubing and they measure to be 12 ga and 16 ga. 12 ga looks like it would be considerably more difficult to bend by hand, although I could use a torch to help get it in shape. 16 might actually be closer to what I need.

The gussets I was thinking of would actually be more like a sheet that wrapped around the intersection like a box, instead of as two triangular filler pieces like in the original photos. I've attached a pic with the box outlined in yellow. I've seen this once with dimple holes in all 4 triangular sections, presumably to lighten and stiffen the gusset.

My hunch is that this gusset will stabilize the X-junction of the door bar. This would stiffen the frame in the vertical direction. I thought it also might aid in horizontal (side-impact) since the inward bending force would have to first defeat the weld at the intersection of the X, and if the gusset was fully welded the gusset would resist the inward deflection of the tubes in shear, where the sheet metal would be fairly strong.
Ian

[streetwerkz]

I did werk on a BMW factory equipped pro category road race vehicle and the style gusset you are talking about on that vehicle was 16 ga max.
been a few years so I don't remember exactly what gauge material, I do remember it was 16 ga, or lighter.

Probably the same material as the tube wall

[idickers]

Thanks! Those were exactly the type of gussets I was thinking of.
Ian

[Izzy]

Originally Posted by IZwack

School me: why does there even need to be a gusset at that intersection? The plane at which the gusset are intended to aid in is perpendicular from the force (side impact).

Even when done correctly, 3 bar X's can fail in the HAZ of the main bar. I no longer build a 3 bar X. All of mine are either single bend or double bend.
Single bend

(This is a pretty complicated gusset as it actually curves. Since this one, I've figured out the pattern to make one continuous wrap, but this way works too)
Double bend:

[Izzy]

Oh, and if you go with a 3 bar X, you'll want a gusset in either the top or bottom triangle as well for the reason pictured above.

[IZwack]

Ah okay thanks for the pictures.

[TheBandit]

Ian, do you have a build thread going? I'd like to see what you're putting together.

[idickers]

Originally Posted by TheBandit

Ian, do you have a build thread going? I'd like to see what you're putting together.

I should start a thread, but it's taken so long to get to this point that I keep saying, "when I get going I'm going to post some stuff", and I never feel like I'm getting anywhere

EDIT: I do have a blog on the build now: http://www.bmw2002faq.com/component/...ghlight,redux/

I have a 1976 BMW 2002, which I use as a track car and weekend driver. Over the years I've upgraded the brakes, engine and suspension to make quite a nice track car. I've done all the work on it over the years, partly to save money, and partly just to learn how all the stuff works! It blew an engine back in '95, and I learned a lot putting in a fuel-injected engine from an '89 BMW M3.

Recently, I wanted to put a cage in the car, partly for safety, and partly to stiffen up the 30 year-old chassis. Thanks to BendTech Pro, the Tube Bandit, and my trusty Pro-Tools 105HD bender, I've started to make progress. Since this car will also be driven on the street, I wanted the cage as tight to the body as possible. It took a couple of tries, mostly figuring out how I screwed up the measurements, but I finally have begun to get a cage I like.

Here's the main hoop. I wanted it set back behind my seat to keep it away from my noggin, and tight to the inside, and tight to the rockers at the bottom.




I also wanted to keep the A-pillar bar tight to the rocker, and turn it high (again away from my noggin) and back to the main hoop. This was the most difficult bend, since from the main hoop it bent down and out, and then straight down at the base of the windshield.



I also wanted to get the cross bar on the windshield high and snug; here is a pic with the A-pillar bars tacked in place and a string to mark a reference line between the bars. The actual bar goes up and forward from the apex of each A-pillar bend.


I've got to say, the combination of BTP, the Tube Bandit, and a POB bracket are incredible. They really give the home shop builder like myself the opportunity to make some precise structures. The only downside is that in order not to waste tube, I like to feed the sticks of DOM into the bender and then cut off the last bit when I'm done. Unfortunately, the weight of the tube bends the stick and puts a twist into the tube that screws up my calculations. I tried bribing buddies to come over to my house , but they just weren't reliable. Maybe it was having the beer before the bending?

Anyway, I built an "assistant" out of scrap tube (which I had a lot of from calibrating and learning to use the bender). So I made an adjustable-height support that had a roller on top, so I could feed tube in at a constant height. Some HF castors allowed me to wheel it around one-handed, for cases like the end of bending the main hoop, when the structure coming out the bender starts to get heavy.


So that's where I am. The gussets will come in the next step. I picked up some of Barbed Wire Offroad's dimple dies, and will use them to dimple the gusset at the X-door bar.
Ian

[Graham08]

Looks really good, Ian!

To me, getting a cage to fit well in the car is a sign of excellent craftsmanship. It's obvious you've spent a lot of time and effort to get to this point. Please keep us updated!

[idickers]

Here's the plan I'm working off, drawn up in BTP. The blue or black tube is 1.5" x .095 DOM, the green or orange tube is 1.5" x .065 DOM. The cage is triangulated to the front shock towers ahead of the cockpit, and to the rear shock towers and the diff in the back.

Ian

[Flatline's Up!]

looking good man. I used to be in the '02 crowd a couple years ago.. they're fun little cars with tons of potiential built in

[idickers]

I had some time to work on the cage again, and got my doorbars roughed out. I have a tube running along the rocker between the A-pillar bar and the main hoop. Because the main hoop is just inboard of the rocker, while the A-pillar bar sits on top of the rocker, this rocker tube had to turn inward at the end to meet up with the main hoop. Intersecting the rocker bar at each end where it meets with the vertical bars is the curved lower door bar.

These door bars required some careful fishmouthing, but I think they came out nice. Bend Tech Pro was fantastic for fitting complex intersections of tube. I found the wrapper option in the cutting menu to be really helpful, especially on steep angles like on the lower door bars, where I can't use my JD2 Notchmaster. I traced the pattern from the wrapper, and used a 4.5" angle-grinder setup with a 1/16" cut-off blade to cut the pattern, then smoothed it out with a carbide tip on a die grinder.

And of course, Tube Bandit made all the bends accurate and repeatable (anyone want to buy a degree ring for a Pro-Tools 105 bender?). After muscling the tubing around to get exact POB readings and bend angles for the A-pillar bar, it was pleasant to do nothing more than make a single bend in some tube for a change.

I'm going to include two vertical bars on either side of the intersection, and will make a gusset out of 18 ga steel over the weekend. The bars are tight to the door to give you room, but I'm going to have to change the angle of bend for my car, as the upper bar interferes with the window crank in this version. It means I can only roll the window up and down with the door open; not a problem in a race car, but not desirable on a dual-purpose car

[idickers]

I worked on the gussetts today. I wanted to box the intersection where the door bars join, but didn't want to have the added height on top, to make it easier to climb over the door bars. I settled on boxing the intersection on three sides, and made a gussett out of 18 ga steel.

I had some scrap 18 ga from another project. It had a work-hardened corner on the bottom so it wouldn't fit right, but I flipped it over and used it as a test piece anyway. I made the gussett out of one piece of sheet metal, and trimmed it to contour the top of the "X" of the door bars. I used the bars as hammerform to fold the tube over, and it will get welded down the seam on top, and along all the tubes. A couple of dimples added stiffness and bling, and I think I have a usable design.

Now to find some more 18 ga and make these for real.

[idickers]

Picked up some more 18 ga and made the gussets for the door bars. Here's an in-car test fit. These are actually for a friend's race car. I think for my car, where I need to use the window winders, I'll extend the low spot in the "X" forward to clear the handles. In this case the upper bar will actually look like this: \____/ instead of like this: \/.

[Graham08]

Looking good, Ian!

Are you planning on putting a short piece of tube between the dimpled holes to keep water out?

[idickers]

Thanks. I like the idea of the short connecting tube. It's kind of cramped for welding, but I probably will.
Ian