Friday, August 15, 2008

Front Rack Mounts

This week, in the evenings, I've been working on the front rack mounting points. These have to be extremely sturdy - they will be supporting the weight of 440 pounds of batteries, and will have to handle acceleration and deceleration, too (not to mention the forces of a collision, Heaven forbid). I started with 1 1/2 inch box tubing, with 3/16 inch thick walls. I cut it to the desired lengths with a chop saw:

Here are the lengths of box tubing precariously balanced close to where they will end up. I did this to get a sense of where the top rails would be relative to the motor mounts:

A closeup of one of them shows the angle at which it crosses the mounting point - roughly 13 degrees:

And, of course, what would a good summer garage project be without hornets (scroll to the end of that post)? They seem attracted to the buzzing sound of power tools. I've spent almost as much time chasing these nasty little bugs as I've spent working.

Anyway, back to the real work. I removed the engine mounting brackets, which will get box tubing posts welded to them. After getting everything cleaned up, here is all of it (the driver's side bracket is on the left, the passenger's on the right):

There are little lips at the edge of the engine mount brackets. So I ground them off (my wife Jill got a nice spray of grinding sparks as she took this picture - oops - a definite case of "if you can read this you are too close!"):

I then welded the 8" box tube posts to the mounts. Despite the 90-degree weather, I'm wearing long pants, long sleeves, and heavy gloves, to avoid "weld-burn" which is pretty much exactly the same as sunburn:

And here are the brackets, with the posts attached:

They fit nicely in the engine compartment, very even and with ample clearance for the engine mounts:

I test-fit the rack to decide how far down the cross beams would go:

And here is what I decided - to knock off roughly 1/4 inch more in height so that the hood will definitely clear the batteries:

I welded the cross-members to the brackets:

I'm definitely getting better at welding. These are possibly the best welds I've done to date - these were just wire brushed to get the flux crap off - no grinding involved - these are the actual weld beads:

And here are the nearly complete brackets / mounts in place in the engine compartment:

...with the rack sitting on top:

With the mounts nearly complete, the assembly is sturdy enough to place an actual battery there for the first time. Looks good....

However, I've learned that looks can be deceiving. So, I performed a test. I took two pieces of foam-board (which together are slightly thicker than the plastic top plus hold-downs will be) and smeared sticky oil around on the top so I could see if it actually touched the hood when it is fully closed. As you can see, no oil ended up on the hood. This is the battery that is most likely to interfere with that diagonal structural member. But nothing touched, so everything looks good to go:

Next up - finishing the front rack by creating the lid. Originally, I was going to build a complete rack box up around it. But now, I think that is overkill. Instead, I'm going to weld 3/16" angle stock 1.5" wide together into a hold-down, and mount that over the plastic lid. And then screw the whole thing on with 8 3/8" threaded rods. Should be more than strong enough against lateral and vertical forces.

One more detail - I need to figure out some bracing for lateral and front/back motion. The mounts as designed are fine for the simple vertical forces, but the day-to-day acceleration / deceleration / turning forces will eventually weaken them unless braced.

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