Tuesday, January 1, 2008

Turning Trash Into Armor - Building a solid rear bumper out of scrap angle iron.

When your bumperettes or cheapo tube bumper isn't enough protection for the rear of your Jeep, consider this inexpensive and indestructible alternative.

I decided I needed to upgrade my rear bumper for a few reasons. The old bumperettes where OK, but they didn't offer protection across the entire width of the rear end, and were damaged from a prior owner. The fact that they are 2 separate units forced the frame to take more abuse in the event of an impact. Lastly, the bumperettes offered no secure place to attach tow hooks.

The quest for my new bumper began at a local scrap yard where I picked out a piece of angle iron suitable for the job. The piece I chose was a 4"x4" angle at 5/16" thick. This is a bit heavier than necessary, but I figured that I wanted a bumper that I could weld a 2" square tube under at a later date and have a receiver hitch built in. Plus this way, I could pick up my Jeep by the bumper if I ever had some reason to want to do this.

Here's some photos of a stock bumperette, and the frame that is exposed once they are removed.

Weighing in around 65 lbs, I brought the angle iron back to the shop where I cleaned it up. I started out with a wire brush to knock the rust loose and take off dirt from scrap yard. Then I cut it to length with a hacksaw (Use a jigsaw or torch if you have one handy... unfortunately, my blades were old, and literally couldn't cut it.) The length of your bumper will depend on your application... You may want want a bumper that protects the body more by extending out further, or a bumper that is narrower, and less likely to snag on rocks in extreme situations. I chose something in between, extending about 3 inches past the side of the frame.

The next step is to round of the corners, again with either a hacksaw, or jigsaw. Once the rough shape is cut, break out your files and grinders, and smooth over every corner and rough edge. This should be done for 2 reasons. First of all, a sharp edge on your bumper isn't very friendly when you walk by in shorts and brush against it, but also, a rough edge is more likely to cut a tow line if winching angles bring the line across a sharp spot.

After I shaped the corners into a smooth radius and rounded every sharp edge, I belt sanded the entire piece to finish removing any surface rust and prepare the metal to receive a few coats of paint.

Next I laid the old bumperettes on top of the new bumper to be, and marked where the bolt holes needed to be drilled. To be sure you have the holes marked correctly, measure the distance between the bolt holes for the left bumperette and right bumperette on the Jeep frame, then double check those distances on the angle iron.

When the holes are all marked, the next step is to drill them. A heavy duty drill with sharp bits is best for putting holes in steel of this thickness. Be sure you lubricate the bit with cutting oil or you will quickly dull your expensive bits. Also at this point you can locate the positions you would like to mount your tow hooks, and drill for them as well. In my opinion, you are better off having the tow hooks closer to the center of the bumper than out on the outer edges like some people choose. If you are trying to pull someone by a tow hook and it is attached on the outer edge of your bumper, it is more likely to cause you to lose traction on the opposing tire, due to the torquing on the bumper, and under extreme towing will cause the Jeep to sway off course. After the holes are drilled, file the inside of each hole to remove burrs, which otherwise will stop the bolts from sliding in freely. If left on the surface of the metal, the cutting oil will prevent the paint from adhering properly with the metal, so use thinner or some other solvent to remove traces of the oil.

Next I applied 2 coats of primer spray paint. I used a Krylon product that claimed to convert rust chemically into a durable finish. I don't know how effective it would have been on a badly rusted surface, but I was happy to see that the surfaces that had been rust colored were black after the 2 coats, while the clean metal surfaces appeared to have a clear coating on them. I guess this means the product works.. I'll let you know in a few years when the paint has had the opportunity to show its flaws.

3 coats of black Rustolem sprat paint (with a light sanding in between) went on next. The bumper was beginning to look very nice. I sanded and painted the 2 tow hooks while I was at it, not trusting the thin coat of paint they came with. It's easier to do it now that they are not attached to anything than later when they are bolted on.

The last 2 coats of a clear enamel brought out a shine that made my bumper look better than many after-market manufacturer's cheap finishes.

After letting the paint dry, the last step in the birth of my bumper was to bolt it onto the back of my Jeep. There are many different grades of "Inch-style" hardware;

grade 1, grade 2(commonly referred to as "butter bolts"), grade5(commonly referred to as "automotive grade"), grade 8(commonly referred to as "tractor grade"), to name a few; the most common, for automobiles, is "grade 5". As the number rises, so does the "hardness" and "toughness" values that the bolt must meet, so, a grade 8 bolt, can be torqued much more, and hold much more, than a similar grade 2 bolt, and, similarly, using a grade 2 bolt, where a grade 8 bolt is required, can, and will, cause bolt failure, as the grade 2 bolt, quite simply, will not "hold up" under the harsh demands intended for the Grade 8 hardware. Although grade 5 should have been strong enough, I decided to replace the stock grade 5 bolts with new grade 8 bolts. With tow hooks capable of handling 10,000 lbs each, I didn't want to weak link to be the bolts holding the bumper to the frame.

And here is the finished product!

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