I've been wanting to take some drawing classes in downtown Portland, but I was restricted to using a small sketchpad that would fit in my backpack. Then it struck me that none of the art students could SAFELY carry their art portfolios via bicycle without discomfort.
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Step 1: Eyeball Everything
I've yet to see two carriers look the same from bike to bike. So, what works for mine, may not work for yours.
I picked up some aluminum from Home Depot for about $25, along with some metal screws and nuts, and some wire-hanger-thingies.
It's pretty simple in it's design, and I'm still trying to thing of ways to refine it to make it more sturdy, more versitile and (relatively) quick release.
Any and all comments would be appreciated.
Step 2: The Basic Frame
I first built a "square" using the largest of the L-Aluminum pieces on the bottom to be the holder.
Step 3: Middle Braces
I added a middle brace that was parallel to the carrier which added a great deal of stability but didn't do anything for the corners. I used zip-ties for now but will think of some more permanent solution eventually.
The diagonal piece really helps the rear corner stay stabilized.
Step 4: The Holder
I added a second lenth of L-Aluminum to make a sort of gutter that the portfolio can sit in. It's currently taped into place, which works OK for now, but I can see in the long run that this will either have to be glued or bolted into place.
Step 5: Finished and Strapping
It does shake a bit when the bike moves side to side, but overall it's strong and a bit flexible.
I rode it from Mt. Tabor to downtown Portland which is about 5 miles and it held up really well.
I currently use some length of bungie cord wrapped top-to-bottom, but it seems to slowly creep backwards from vibrations so I will get another bungie to hold it in place front-to-back.