Current debate is over removing roof to install cage.
I'm an advocate for de roofing. Tack weld bars across the door opening to keep from spreading or closing during construction.
My main argument is while you can drill holes and drop the cage down to do some welds the rear brace tubes going from the top hoop back to the rear are extremely hard to weld. They can only be welded in once the bar is up in place.
Then once the cage is installed ( and painted ) you weld the roof back on.
In reply to frenchyd :
It seems to depend alot on what type of cage you want to do and what car it is.
Using holes in the floor on top of plinth boxes, I had lots of room to weld the top of the cage and make it fit nice at tight to the roof in my fox mustang, but I also didn't have any seams to cut into, that would be easy to weld back together, like what most newer cars have. If you are doing a lemons car, it may not matter, but welding a roof with no seams will usually end in some sort of distortion in the sheetmetal and cutting down at the base of your pillars could go good/bad depending on the car. Most rollcage rules want your rear braces to be near 45 degrees, which usually gives you a decent angle on welding to the main hoop. But again, a mustang being a hatch, I had plenty of room to crawl in the back to weld.
My biggest issue was trying to weld the main hoop and front down bars in, since they fit tight up to the body. I could weld 75% of the bar to plinth box, but that last 25% would have been impossible. I ended up shortening the window bars to running the feet within the door frame, which led to a somewhat cramped cage.
I do it both ways. It depends mostly on how much of the original internal roof structure I want to retain and that's mostly driven by the rule book. On one extreme are cars that are going to have full interiors installed in them. On the other are, mostly circle track cars where there's no glass, the windshield is a wire mesh and the roof is just a single layer of sheet metal that roughly approximates the shape of the original.
If you're going to have to restore the original internal roof structure and fill the seams on the outside it's probably just as quick to leave it in place. Yes the rear braces can be a pain but with some careful planning, a little welding by sound and some slag inside your clothes they can be installed with the roof on.
I vote holes in the floor. Cutting a roof off is easy, but it's a major scope change to stick it back on and make it look even just ok. Holes in the floor, remove the glass, and cover with boxes had been my go to with my variousl lemons projects over the years.
As said above it's very car dependant and cage design as well. I go out of my way to not cut the roof in any way.
The smallish Tweco flex head mig gun had been a life saver here but I was generally able to get the job done with a standard Hobart gun.
jgrewe
HalfDork
6/7/21 7:33 p.m.
Two holes to drop the main hoop, that is all you need.
With plates over the holes, you assemble the cage(wedge it in there somehow) from the main hoop forward and weld up as much as you can at the top of the A pillars. Lay the main hoop back and drop the front down to weld the parts you couldn't get with it jammed up in the car.
Bring the main hoop back up to the front assembly and weld as much as you can. Pull the plates and drop the main hoop through the floor, weld the parts you couldn't even see.
Raise the whole thing back up, slide the plates in, weld all the plates and the cage to the plates.
Rear supports don't need to go all the way to the top of the cage, just within 6" from the top. No problem there reaching all the way around.
I have cut a small flap in the roof to weld the top of the rear bars and the top of the forward tubes. Easy to weld the sheet metal back in place.
Don49 (Forum Supporter) said:
I have cut a small flap in the roof to weld the top of the rear bars and the top of the forward tubes. Easy to weld the sheet metal back in place.
This.....after you've done as much as you can with holes in the floor.
Don49 (Forum Supporter) said:
I have cut a small flap in the roof to weld the top of the rear bars and the top of the forward tubes. Easy to weld the sheet metal back in place.
That might be an answer, modified. Instead of a flap I could use a hole saw and MiG weld the cutout back in place. My concern with a flap is causing a kink where it bends up and spending a lot of time with a body hammer and dolly getting the roof back together.
