Building Tubular Corner Gussets
Metal fabrication tips and tricks
Adding corner gussets to any tubular structure like a custom bumper, rollcage, tire carrier, crossmember, and the like is a great way to add strength to the corners of whatever you are building. Without corner gussets or triangulation we have to assume that a structural box, even a well-made box, will fail at the corners and collapse as flat as a pancake. There are several different types of pre-made corner gussets available from various off-road parts suppliers, but one of our favorite looking, and very strong corner gussets is something you can pretty easily make once you've learned how to bend tubing, and cope, or notch the ends of tubing. Here's how we make our corner gussets, a design that we openly admit we stole from our good buddy, and amazing fabricator, Rob Bonney from Rob Bonney Fabrication.
First Bend Some Tube
You can make corner gussets out of straight pieces of tubing with the tube bisecting the inside angle of the corner, but adding even just a few degrees of bend to a corner gusset gives it a much more appealing look. We start by adding about 10 degrees to our gussets. We also usually like to use slightly smaller tubing than the primary tubing used. So in this case we are using 1.75-inch .120 wall DOM. For the corner gussets we are using 1.5-inch .120 wall DOM. The smaller tubing generally has a die with a tighter radius than the larger tube, and this allows us to "beat" the bends through the corner.
Mark and Trim Down the Ends
Next we lay the slightly bent bit of tubing on a flat surface and mark the center of the bend on the inside. From there we measure 4 inches one way and 4 inches the other way. This sets the overall length of the gusset at 8 inches. Then trim off the excess material. Because the tubing bender requires a minimum length, you'll need to trim both ends of the tubing. If making several gussets, just start with a long stick of tubing and make them one at a time, making two cuts for each gusset.
Mark and Notch Those Ends
You'll also want to mark the center of the inside of the tube while it lies flat. This will help you with the next step, which is to notch or cope the ends. The best way to do this is using a tubing notcher. Since our bend is about 10 degrees, each notch will have to be set at 50 degrees (forming a 40 degree bend). This, minus the 10 degrees we added to the tube makes for two 40 degree copes in the gusset that are in total 45 degrees, for a perfect 90 degree corner. Now most corners on any 4x4 are not exactly 90 degrees. Many are larger, and many are smaller. You'll have to adjust your cope either using the tubing notcher or
Adjust the Copes for Each Specific Corner
After coping the ends of the corner gussets, we either adjust the angle of the cope using the tubing notcher or by using our handy-dandy 4 1/2-inch angle grinder with a flap wheel. Adjusting the position of the cope is something that takes some time and experience. Generally if the cope isn't fitting correctly, it's because part of the cope is hitting the intersecting tube early and causing a gap. A little gap is good for welding (especially when using MIG), but too big of a gap could yield a weak and or ugly weld.