Custom Bumper Questions: d-link tab and wall thickness

I am in the middle of building a custom rear bumper for my 89 cherokee. I have a couple of strength questions. I am trying to build a strong and light as possible bumper that is capable of being used for recovery. I do not want this to be way overbuilt like a lot of the bumpers out there. I am not looking for a 300lb slab of steel hanging off the back off my truck.

First question, How thick does the rectangular tubing have to be for the main body of the bumper? I plan on using 2"x4", is 1/8" go enough or do I have to bump up to 3/16" or 1/4".

Second, How thick does the wall of the D-link tab have to be? I was planning on using 1/2" or 1/2" + 1/4" welded together for the body of the tab. But when I drill the hole in it how thick does the wall between the hole and the air have to be?

The mounts are almost done, they are built out of 1/4" with grade 8 hardware for the hitch mount and grade 5 for the stock bumper mount. You can see some pictures here. http://userweb.suscom.net/~navitp4/web_bumper/index.htm

Thank you for the help.
katarn

looks like a good start.. thats the only way to mount a bumper!

design will dictate in large part what materials you use. I used 2x4 .120 (1/8) wall for my rear bumper, but I have it oreinted so the 4" section is horizontal, this way is much more resistant to bending from a pulling force. Mine is welded between the frame on my MJ with triagular gussets also, total of 30+ inches of weld to the frame.


With an XJ I would imagine you would orient the 4" section vertically, in which case it is more likely to bend, this can be resolved by thicker material (3/16 should be adequate) or gusseting on the back side.

The mounting of the shackle is VERY important, it is literally an issue of life and death. 1/8" is pretty thin so you need to mount it in a way that it will not tear the tubing. For my D-ring I wrapped some 3/16" strap around the top and bottom of the 2x4 so that there is a total of 20+ inches of weld holding the D-ring to the 1/8". For the type of recovery shackle you are talking about, one good step would be to sink the plate through the face of the bumper to the back so that you can weld it to the front and the back of the bumper. 1/2" plate will be plenty for straight pulls but can/will bend on side pulls, so 3/4" total might be nice. There are a few shops that sell these plates and I think would be worth buying rather than all that cutting/grinding/drilling.

I appreciate the comments. The 4" dimension will be vertical. The metal that the d shackle mounts to will go through the 2" part of the rect tubing and be welded to both the front and back. I might also put a plate on the back to distribute the stress on a wider area of the tubing.

I plan on using something like this http://www.warn.com/works/accessories/5-8dshackle.shtml
but that is link is just for a picture, not that actual one. I have no idea what specs I am looking at yet.


Thanks
katarn