Given my power level and the length of the primaries, I decided to step the headers from 1-7/8” (green blocks) to 2” (yellow blocks). This required the headers to be redesigned and the new version rubs four of the 2” x 2” chassis tubes.
Top and slanted tubes have been scalloped
The solution was to scallop the top and slanted chassis tubes. I wasn’t worried about the chassis warping during cutting or welding because I had the new gussets and temporary steel cross supports discussed in the previous post in place. As can be seen in the picture above, the cut in the top tube is larger than the slanted tube. While 90-degree cuts would have been easier, 45-degree cuts were used to prevent stress risers. Cutting the tubes was tedious and after some experimentation, this is what worked best:
Holes were drilled in the 45-degree corners.
An angle grinder with a 4-1/2” abrasive cutoff wheel was used to plunge cut the vertical face.
A Dremel with an abrasive cutoff wheel was used to plunge cut the 45-degree angle from the previous cut up to the holes.
A reciprocating air saw with a Bosch T227D blade was used on the longitudinal cuts. 8 TPI seems too aggressive for aluminum, but that’s what the blade was designed for and it works well.
The Dremel and a small right-angle grinder with a 2” abrasive wheel were used in areas where the other tools wouldn’t fit.
A combination of a 6” orbital sander, a right-angle grinder with a 2” sanding disk and a deburring tool were used to clean up the edges.
The tube has 1/8” walls and since I was removing material I decided to oversize the inserts. Fortunately, McMaster stocks 3/8” x 1-3/4” tall 6061 bar, so I didn’t need to trim the height. Scrap pieces of round and right-angle steel were used to fabricate male and female dies to bend the material. The dies had no provision to ensure alignment so the male die, female die and material had to be carefully aligned with a small machinist’s square for each bend. Given that only eight bends (nine if you include the test bend) were needed, it worked well enough. For each bend I applied duct tape to the three locations that come into contact with dies to reduce marring.
Male and female bending dies
The dies where placed in a hydraulic press and a digital angle finder was used to determine when 23.5 degrees was reached. Since I wanted a 45-degree bend and the aluminum is being pressed into a right-angle die each side should be 22.5 degrees plus one degree for spring back.
The dents made by the dies were sanded out of the front and back sides to reduce the potential for stress risers. The bending process causes the sides to deform and these bulges must be sanded flat for the piece to slide into the chassis tube. One that was done, the ends were rough cut on the bandsaw.
The edges were then trued up with a 3/4” end mill. Fixturing was as simple as dropping the piece in the vice and tightening it. This ensured a perfect fit with the inside of the chassis tube.
We anticipated that once the piece was inserted into the opening we wouldn’t be able to move it into place or remove it to trim it so we drilled and tapped two 1/4”-20 holes which will be used later to mount a heat shield. However, once we had inserted the piece we had a hard time using the bolts to move it. Abe then had the idea of using a slide hammer so he welded a 1/4"-20 screw to a 5/8” nut to adapt it to our tapped holes. It worked perfectly.
Pre-weld fit up is excellent
Fully welded