Tuesday, March 1, 2011

And, then again....

Sometimes it just makes sense to stop with the research, postulating, theorizing and planning and just grab some tools and start working.  I recall a teacher or college professor that once said; "just put something down on paper.  You can always go back and edit it but at least start writing."*  Obviously, starting was the hard part (and still is, for me).

I had decided that using square steel tubing was to be easier than to experiment with bending round steel tubing.  There are too many ways to mess up round tube, with respect to bends, and end up with various lengths of unusable tube.  Also, there's a science to creating the flattened tube ends (where the bolt holes are).  You can't just smash the tube flat (with a hammer or vice) and drill a hole.  If you use the brute force method, you're likely to end up with the tubing wall splitting or breaking off as it fatigues from vibration.  Thanks to some shows on cable, I've seen the tooling required to do this right; it involves various die shapes as well as presses with several tons of force.  Honda chose at least two methods, on the NX alone, in which to form 'smashed' tubing ends which will last; one involves the method mentioned above and the other involves inserting smaller diameter tube within the main tube ends and then 'smashing' said tubing.

So, I opted to use 1/2" square tube and was resigned to the fact I would have to experiment with slot cuts to create offsets (to clear various obstructions).  Well, I was happy to discover that by using a 5/16" spacer (at the seat bolts), I could use a straight piece of tube for the load bearing member.  The area in red, in the illustration, is one straight piece of 1/2" square tube and the load is supported by the bolt that holds the seat as well as by the turn signal.  I can use 3/4" square tube to fabricate the rack base plate support.  I may not even need to form a rectangle, I'm thinking a "U" shape will do the trick mostly due to the fact that the (Givi E200) base plate will be bolted on top (this will strengthen the rack assembly even further).  My only concern, with respect to stresses involved, are the attaching plates at the turn signals.  They're only .060" (1/16") thick.  To compensate, I plan to have the 'risers' be only tall enough so that the "U" shaped base just clears the rear fender.  This should keep side loading to a minimum (which, hopefully, won't fatigue or cause those plates to bend).

*(or something to that effect)

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