Not framebuilding, But Framebuilders Will Know -- DIY Roof Rack for Tandem
Framebuilders are metals and materials experts, so I'm sure that you guys will know this...
I want to build a bike tray for my existing Yakima roof rack for for my Canondale tandem. I'm too cheap to pay $350+ for a Yakima, Thule, etc., tray, so I thought I'd build one. My plan is to imitate the design of a RockyMounts bike tray for tandem
With this system, you leave the back wheel on the ground while you attach the front fork (because the fork attachment point swivels), then pivot the tandem up and attach the the rear wheel.
Here's my material's list:
* 1.75" x 1.75" x 0.125" wall 6063 Aluminum Square Tube or 2" x 2" x 0.1875" wall 6061 Aluminum Square Tube for the primary longitudinal member (about 78" long) and for a short (~10") piece that will attached to the main member by a 3/8" bolt as a pivot point and to which will be attached a fork skewer like this:Since I don't weld (not aluminum, anyway), I'll hire a pro to tack-weld the forkblock to a piece of 0.25" aluminum plate, and then tack-weld that plate to the swivel piece. I'll also have him tack-weld the main longitudinal member too two 4" x 4" x 0.25" plates at the same spacing as the "cross-bars" of my existing Yakima roof rack system. I'll attach those plates to the cross-bars using u-bolts (hopefully, with some sort of tamper-resistant nuts). A 12" x 12" x 0.25" plate is $31.00.
What do you think of my materials selection?
Would you suggest something else?
Or is there a smarter way to tackle this problem?
I would get a fork & tray type system from whatever manufacturer, and then use a 1" x 2" piece of 8020 aluminum extrusion of an appropriate length. You shouldn't need much more than a drill and the appropriate hardware to put it all together, and as a bonus, it will be easy enough to modify if you get a different tandem or a different car. I definitely wouldn't weld it.
I don't think i'd design the project around welding either unless you were using steel. By the time you pay a pro to clean, layout and then weld (not tack weld :-) it all together you will have an hour into it. Most fab shops are $65-80 an hour.
The fork clamp will bolt right to the 10" block. If you use machine screws countersunk from the bottom they won't interfere with the pivot action.
I would think you could find a source for aluminum in yours or a nearby town. It would have to be better than online metals.
Fyi, when I do a project that requires al to be bent I order 6063, otherwise I use 6061. The 6061 'will' bend but it doesnt' look right and thins out and micro cracks in the corner where it doesn't stretch right. Not sure if this will have any bearing on your project or not but I thought I'd add it in there.
I really like the idea of clamping the fork and then lifting the rest of it on the car, just loading a normal bike is tough- I couldn't imagine a tandem!
The only other thought I have is the attachment of the tube at the rear roof rack. This spot is going to take the brunt of the punisment.
I think you are going to want to beef it up as much as you can due to the twist that is going to happen there.
Petes note guiding you towards 80/20 is a good one. Search thier website for ideas and then shop for small amounts on ebay.
I have a hunch you will find a really elegant solution for the pivot as well.
Good luck with the project!
($40 in 97" length from Amazon) and buy something like this:
on Ebay or Craigslist (typically can be found for about $50 or less), then cut the manufactured "bike tray" (in this illustration a Yakima Copperhead, but could be many other brands or models) and then attach the two pieces to a piece of 8020 that's long enough to support the tandem?
If I understand the suggestion, then this plan looks a lot simpler and faster and simpler to build -- plus the 8020 looks like it should be much, much stiffer than what I had in mind, which should make it more secure and long-lasting over time.
THANK YOU, THANK YOU, THANK YOU for the gift of your time and advice.
As a hobby builder who has used an Atoc since Charles' first semi production run and having worked in a tandem shop let me lend you my comments. The fork clamp pivot is easily dome with the QR set a bit loose, the axle pivots within the QR and axle clamp. then tighten the Qr fully after the bike is up. the swinging pivot gets a lot (repeat A LOT) of side to side forces. each of my 3 Atocs suffered from some slop here. None have ever been a problem but design with a HUGE margin for this pivot. I have wondered if a loose pivot with a couple of QR type tightening devices on either side of the pivot might be a more solid and more likely to last design. Having the side wobble forces taken up by the 2 QR bolts instead of the sole pivot bolt. the rear tire really doesn't need a trough to sit in. Just a tight toe clip strapping on the beam. The Velcro Atoc straps can come loose after many highway miles (especially with a rain storm)... There's also a LOT of vertical load on the beam at the rear wards load bar point, depending on how far apart the load bars are. The Atoc, with it's sliding and removable, rear section of the beam has some slop over bumps. Again never a bending issue but I might add a second section of beam to reinforce the beam around the rear load bar. Lastly the front load bar and beam junction has a lot of twisting forces (see second comment) Any thing to spread this out widthwise along the load bar is good. Andy.
Actually, I would get something like this for the rear wheel tray:
unless you wanted to make several of these, in which case, get the longer tray and cut it down to length.
Rocky Mounts also makes bar clamps that look like they should work with the 8020 extrusions. The 8020 should also be plenty stiff/strong, and as it is anodized, should hold up to the elements well. I would make sure to get all stainless hardware, though.
Though it sounds like you are on your way, one of the problems with raw stock is that it isn't anodized and can be quite dirty to handle. One problem with welding Al, is it can need heat treating. Suggestions so far bypass those problems.
The Pro team Race support cars don't use the erector set approach to their racks.
they are built of steel and are one piece when they are done fabricating them.
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