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DIY shelf instructions
I'm writing these instruction for a 3/16" thick aluminum shelf. The bolts lengths can be adjusted for other materials thicknesses, but i recommend working with 3/16" aluminum in this case because it is plenty strong, stiff, light weight and easy to work with (e.g., cut and shape).
Mounting bolts: two button head M8 x 1.25 X 70 mm long, two button head M6 x 1 x 60 mm long, zinc plated or stainless steel. Or, if you have the ability to make a 90 degree countersink hole you can use flush socket head cap screws.
Spacers: 5/8" Diameter (16 mm) drilled through center to accommodate bolts. Two 5/8" (16 mm) long, two 1.3" (33 mm) long.
Rear mounting plates: Two plates 3/16" thick aluminum, 1.5" x 2.75" (38 x 70 mm)
Two M6 x 1 nylock nuts, zinc plated or stainless.
The diagram below shows the crucial data for mounting a rack using the spacers noted above. The two holes for the 8 mm bolts are 100 mm apart (3.937") and 125 mm forward (4.921") of the center of the most rear center slot in the stock rack that came with the bike.
Two plates approximately 1.5" x 2.75" with 1/4" holes (for the 6 mm bolts) are to be spaced 40 mm apart. You can vary that a little of course. Just be sure the holes in the rack match the holes in the plate. You can do that by making the holes in the two plates at the same time and then using the plates as a template to drill the holes in the rack.
The three horizintal lines on thi drawing rprsnt 3/8" slots for 2" straps that would run under what was being carried through the slots and then wrap around the top of what was being carried. Slots could be put on the sides as well.
The sides could be tappered a little to reduce the apparent size fo the rack and blend with the line of the bike, or not.
A simple rack like this one can be cut with a circular saw using a metal cutting blade (It's as easy as cutting wood) and routered using a 3/8" carbide tipped router bit. I milled this one on my CNC mill and will make them available cheap. More to come soon. Contact me for requests. I"M HAVING FUN.