This normalizing is followed by tempering to make the material stronger. Certified heat-treats the parts in large furnaces using multiple rows of electrical conduit, similar to a giant toaster. Their facility can normalize and heat-treat material as small as nuts and bolts and as big as complete chassis or giant structures for cranes and airplanes. Plus they can help strengthen both mild steel and exotic alloy components. In the end the substructures had a hardness rating of 34 to 38 Rockwell, which is similar to a Grade 8 bolt. | 
With the parts back at Poly Performance, Burroughs started the assembly. The Poly Performance fabrication shop has a hefty frame table that provides a flat, solid platform to assemble the chassis on. We started by centering the subframe components on the table and inserted three pieces of DOM tubing between the subframes. In order to have the transmission output centered and the subframe right up next to the Atlas transfer case, we set the parts at 31 inches center to center. Notice the multiple suspension mounting points front and rear and the bolt holes at the bottom for the skidplate. |
With the subframe solidly clamped to the table and three cross tubes tacked into place (we used mild steel ER80S-D2 welding rod whenever welding DOM to chromoly) we moved onto the front framerails. You'll want to find a stationary point that you can always reference in order to make the chassis as square and uniform as possible. We used the centerline of the table, which gave us a point in every direction to start from and then built frames and jigs that were perfectly square and clamped into place to set tubing on before support tubes were built. | 
As we added more tubing, I went from magazine guy to fabricator's assistant. My first job was to cut the tubing to length, and this was done with a wet saw, though a chopsaw, a bandsaw, or even a hacksaw can work as long as you get a good square cut. I had to be sure to double-check all measurements down to a 1/16-inch or better. Once the tube is cut I made sure the sharp edges were ground off and any burrs removed with a grinder or this JMR belt sander. Cleaning the edges keeps the annoying cuts and snags at bay, and helps in measuring for future bends and notching. |
Once the cut ends are free of snags, be sure to clean any oil or rust inhibitor from the tube that was applied at the factory as it can contaminate your welds. Cleaners such as Simple Green work great for this. After cleaning the tubing, mark it for bends if the piece needs bending or determine the angle of the required notch. Poly Performance uses a computer program known as Bend-Tech that takes the CAD drawing and determines the distance from the end of the tube to the start of each bend, the degrees of bend and the rotation of the tube needed to start the next bend. | 
As with the frame buildup on the table, it also helps to have a reference point when bending tube. Burroughs uses an angle finder with a tubing mount that allows him to determine how much the tubing is rotated from one bend to the next. This is extremely helpful when bending mirror-image tubes for opposite sides of the chassis. |
For the actual bending we used a JMR hydraulic bender. This piece can be outfitted with many dies, and has a degree ring and pointer to show what angle the tubing is bent to. Be sure to first determine how much spring back your tubing has. Spring back is the number of degrees (our DOM had about 5) that the tubing must be bent past the desired angle in order to get that angle of bend. For example, the tube had to be wrapped to 48 degrees in order to get a 43-degree angle once removed from the bender. | 
Notching, like bending, requires thinking in an odd three-dimensional style that confuses most people but comes easily to many fabricators. Where a square or flat piece of metal can be cut at a simple angle, round tube that is angled and runs between two other tubes must wrap around the tubes at each joint. And when multiple tubes meet in a structure it is even more confusing. To make it as precise as possible we again turned to a JMR product-the company's tube notcher uses a 1.125-inch shaft supported by Timken bearings. This keeps the holesaw from wobbling around as the teeth cut into the tubing. We attached a Milwaukee 11/42-inch Magnum drill and holesaws to the notcher for reliable torque and long-lasting cutting blades. |
One of the most important lessons to learn when building any fabricated component is to only tack weld parts together. As you build something you'll feel the urge to burn it in solid. But until you have made completely certain that you don't want to change anything-whether working on a rock slider, rollcage, or full buggy-it is best to just do a small solid 1/8- to 3/16-inch weld that can easily be cut out if need be. Most of the main chassis welding was done with a Millermatic 251 MIG welder. | 
Notching leaves the tubing very thin at certain edges and these points should be ground out till the tubing has a more blunt edge with thicker material... |
...The thicker material will result in a stronger weld, whereas the thinner material can burn back when welding and not result in as strong a joint. | 
This month we began the chassis buildup and covered many of the tools that helped make it move along smoothly. Next time we'll cover more of the chassis construction, installation of the drivetrain, and how we finally laid out the tricky front suspension and steering. |