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sj413
03-16-2006, 04:05 AM
Hi, i'm building an BMW E30 325i to race in here in holland but I'm having trouble figuring out how to build the rollcage. I allready know how the design has to be (it has to be according to FIA rules). But I can't figure out how to weld two tubes together.

How do I weld the tube coming from the front (tube B) to the main hoop (tube A). I can't figure out how you weld the side that is near the roof, because I can't reach it with my MIG torch.

http://www.xs4all.nl/~vanderl/dennis/rolkooi.jpg

dude
03-16-2006, 05:03 AM
if you cut a 2" hole at the points where your main hoop and front legs sit, you can drop the cage through to the ground to complete your welds, then lift it back up and do your foot plates! Then finish the back of the cage as you can access it easier.

cheers...jason

Chassisguy
03-16-2006, 05:12 AM
It's a secrete. If I tell you I will have to Kill you. Well I could give you a hint and just whip you but :lol: . Just kidding. The trick is to spot the bottom of the main hoop to the floor. The place the upper in place and weld what you can rearch. the cut the lower spot welds loose, tilt the bar forward and weld the rest.
I usually make my halo bar with a kick in where it connects to the main hoop for easier welding without having to do that.
Hope that helps.
Also, here in the States most of the racing body rules state that if you can weld atleast 80% of the joint then you can install a gusset and fully weld it in place. I like to fully weld mine if at all possible.

Steve@Reliance
03-16-2006, 06:39 AM
I do it the same way as Chassisguy. I tig my stuff with a short back cap so I can get in more places than with mig, but you need a lot more room than you'd think. Just because you see it dosen't mean you can weld it. I have worked on/seen a lot of race cars in my time and I would say the vast majority, -85%, aren't welded on the top 1/3 of the halo bar.

rsanter
03-16-2006, 07:11 AM
I have done it the same way.
tack the bar to the floor, tack the upper loop in place and then tilt foreward to complete the weld on the top loop

bob

zags
03-21-2006, 07:21 AM
I have gone so far as to cut the roof off of cars and weld them back on when done. This was on very elaborate cages in stock cars. You can make the cage extremely close to the body in this fashion and is worth the effort to maximize the available space around the driver. The last cage I built was in a standard cab Toyota pickup that was to retain the stock interior, glass and headliner. Space was at a premium in order keep the driver's head a safe distance from the tubing during a severe roll. The front "legs" of the cage went through the top of the dash panel with a dash bar running across inside of the dash. Because the cage fit so closely inside the cab, I could not lower it though holes in the floor and cutting the roof was out of the question. What I ended up doing was tacking the cage together inside the cab, then cutting the front legs about 24" from the floor. I then tilted the cage forward, fully welded it, then properly butt welded the front legs back together using a sleeve inside the tube and some rosette welds on each side of the joint. It was the tightest fitting cage I had ever built, and one of the easiest to weld.

Peter Miles
03-21-2006, 07:59 PM
What I ended up doing was tacking the cage together inside the cab, then cutting the front legs about 24" from the floor. I then tilted the cage forward, fully welded it, then properly butt welded the front legs back together using a sleeve inside the tube and some rosette welds on each side of the joint.

I like that approach, Larry!