bolting things to rollcage tubing?

[2gofaster]

I can't find that the NHRA nor SFI say anything about this in any of their rules or specs. SFI specs how the holes in tabs must measure and where you can put holes in tabs, but that's about it. What is the consensus on how to bolt something to the rollcage? In my case, I've got 2 floor bars that the seat is to sit on that tie between the inner and outer frame rails. Is it acceptable practice to make a flanged weld nut(take some 1" x 1" round stock, drill and tap the center for 3/8 bolt, and machine a shoulder for it sit against the tube), use a hole saw to cut a hole in the tubing, drop the weld nut in and tig weld it to the tubing? How do the nascar builders attach stuff to the cage members like that if they can't put tabs? Thanks!

[FM117]

Shane
This is not a direct answer but take a look here for
lots of cage photos.

http://e30m3performance.com

click on tech articles then pick roll cage symposium
Dave

[ASKANDY]

I always spud the hole and bolt all the way through the tube. The main tube is drilled or hole sawed and a small tube with an ID the size of your bolt is welded into the main tube.

Andy

[eric75]

Another place to get good roll cage and fabrication pictures is

http://www.desertrides.com/features/

and

http://race-dezert.com/index1.html

I'm not familiar with the regulations, but you want to be aware that drilling a structural element will create a stress riser. So if you bolt through a tube, you obviously need to reinforce the hole.

The through bolt idea like Andy mentioned is probably better than tapping because the threaded components that are subject to fatigue can be more easily replaced. Also the load is applied to both sides of the tube, so it is less likely to go out of round and buckle in a crash.
The through tube idea is required to prevent the tube from crushing under bolt tension. For the smaller diameter tube, I would recommend something with a thicker wall than what you use for the roll cage. (So that the cross sectional area of the small tube is at least 1.5 times that of the bolt).

If you are using thin stuff for the roll cage, a step drill will be handy for off-center holes.
Be careful that your bolts go in straight. You may consider making all your through tubes on a lathe, then assembling them to the seat, and using the seat as a jig while you tack the other side.

[2gofaster]

Thanks! Well the problem is that I welded the floor bars in and there's very little room underneath them. Oh, the power of hindsight. LOL. I can drop a tube with the id of the od of the bolt through and weld it at the top, but not the bottom. With a bolt in compression, though, I think this would suffice. In all actuallity, I will probably make upright tabs to weld to these floor bars to allow the seat to be bolted in from the sides. This was the first SFI spec'd cage I've done and let me tell you..........an upgrade from an existing sportsman rollcage is not the best way to go about learning the intricacies of it. There was a time when I was balled up behind the main hoop trying to weld the funny car cage bars to the top of the main hoop and I thought I'd have to be airlifted out of there. LOL