Sunday, September 7, 2008

Lower Rear Rack, II

This weekend, I completed the sheet metal enclosure that I designed in the previous post. The reason for the enclosure is that this rack is both "outside" and "inside" the passenger compartment, and I don't want fumes, water, road debris, etc. getting inside.

The first step was to print up the plans at a 1:1 scale. Using an 8 1/2 x 11 printer means you have to tape lots of pieces of paper together:

Next, I took the paper patterns outside and test-fit them to the box. On the whole, it fit pretty well - but it shows that a little more height to the sides would not hurt (which I added as I cut the patterns out):

Before welding anything, I used this weld-thru primer on both faces of the metal that would touch (but not be 100% welded). This will prevent rust from starting - and, with the high heat of welding, rust starts almost immediately:

Here's the box with weld-thru primer on any surface that will be touching sheet metal:

I taped the templates to the sheet metal, then used a 4 1/2" cutoff wheel on my trusty angle grinder to cut out the pattern:

Both pieces of sheet metal have a "tab" that needs to get folded up to mach the angle stock on the bottom of the battery rack. So, I firmly clamped a spare piece of angle stock to the sheet metal and used my ball-peen hammer to "gently" form the tab to the 90 degree angle:

Here's the first piece, placed on the box with bending in progress. I used various clamps and weights to keep the metal in place while I used the ball-peen hammer to form the metal around the box:

I then spot-welded the enclosure on to the rack from the inside:

The second piece went smoothly too, very similar to the first piece (only a different pattern, obviously):

And here it is, all welded up. I estimate that I did almost 27 linear feet of welds to close all the seams (you can also see the spot welds that I did on the second piece near the front of the box):

And here is the completed box, with the exterior weld beads ground flat (to give less of a place for rust to start and to allow the box to drop in to the hole smoothly) and the flux residue sanded off:

The box still fits in its hole (although I did have to enlarge the corner near the top-right of the picture - that roughly 1/8" additional size was just enough to make it not fit):

Here is the completed box from below. You can see that it does not come close to interfering with anything. You can also see that the 3/16" angle stock on the top is actually resting on top of the unibody "frame rails" - this is a very good thing, since those are the primary structural members of the Jeep:

Jill asked, "what are those triangular areas in the corners for?" They are for two things - the high-voltage interconnect for the charger (at the most-positive point of the battery chain, on the right side of the box), and for one of the huge 400A fuses that protect the whole high-voltage system. Here is one of the fuses test-fit in the corner. A slightly tight fit, but should be OK. I will likely put some polypropylene in this area to insulate it from sparks / arcing:

Next up: painting this rack (after cleaning the flux crap out of the inside), and building the Upper Rear Rack.

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