Cutting holes in the floor for weld access?

[Seralan]

Hey All,
I'm trying to get back out on the hills this year. God willing I can run a whole season.

I am preparing a Ford Focus for this year. I know I'm going to be over the breakout time, but figure safety first right? Anyway, can anyone tell me if popping holes in the floor to drop the cage through is ok or not? I plan to use far more then 36sq" plates for the final mounting, so it seems like the small holes would be insignificant.

Also, in the rules section, it talks about doubler plating, socketing and gusseting as methods of attachment. I'm familiar with the doubler plates, but can anyone post pics of the other styles?

Thanks,

Alan Grant

[walterclark]

I will answer the first question. Yes. It is acceptable and fairly common to do this, weld plates over the holes once you are done with the welding on the top and then weld the ends of the hoop and A-pillar bars to the plates.

[Mopar 151w2]

If I can get this pic to work.....


These techniques applay more to frame or tubular spaceframe chassis designs, though using them with a footplate won't hurt a thing .Essentially, it means holesawing one side of the framrail or closed section of unibody, so that the cage leg "sockets" into it. makes it much stronger in a side impact, and allows an effective, multi-pass weld with MIG.
As you can see in the picture, the gusset adds more weld engagement than is possible by only welding the circumfrence of the tubing, and spreads load over considerably more tubing than the single perimeter weld.

It was my intent, with all of these items, for the rollcage tube to engage at least as much chassis material, in cross-sectional area, as is in the tube. Example: area of material in cross-section of 1.75 x .093 tube = .484 sq.in. Matching this area in .040 flat floor = 12.1" linear of weld = 3.86" diameter IF all welds are perfect and complete, so the old standby 6" Square footplate represents a reasonable margin of f*&^up
Example of joining 2 tubes in less than ideal conditions (weld 2x tube diameter, per the rules) Circumfrence of 1.75" = 5.50" x2 = 11" linear inches of weld! A 90 deg. gusset, 2.75 " in/side, will get you there. In the case of an internal sleeve gusset (tube splice) of the same size tube, the circumferential weld = 5.50". A plug or rosette weld in a 5/8" hole = 1.57" of linear weld. 6 rosettes, 3 equally spaced on each side of the joint, = 11.8" of linear weld.

[Seralan]

Hey Guys,

Thank you for the replies. I knew I had talked to Charlie North about that technique years ago, but wanted ask. I figured that having this forum, it's better to ask questions here then call Don directly. Easier for people to search later.

My intent is to plate not just a section of the floor but up the rocket and the firewall to tie everything together. I am sure it will be more then enough. I guess I just wanted to hear that seeing the weld bead around the clearance holes under the car wasn't going to end up with me failing tech.

I appreciate all your help,

Alan

[Mopar 151w2]

Extra rasin pie forthe weld on the bottom side of the plate! Bonus if you plug the tube end with a (removable) freeze plug. Shoot WD-40 up in theah every coupla years,

[Seralan]

I have a lot of welding experience but this is going to be my first cage. It should be completely overbuilt, but that will be ok. Trying to cross reference hillclimb, com, and rally America rules and make a cage that is compliant with all of them is tough.

First thing is first though, I have to get the car running after sitting for four years.