If you are a cycling tourist you already know what to search in a good bike rack bag. It has to be waterproof, resistant, capacious, and is has to be fast and easy to fastening on the rack. Actually it's quite frustrating having to untie many straps in hidden places behind the bags, every time you need to remove them.
Step 1: The Hook
There are good solutions on the market, bags like Ortlieb and Vaude have all you need, and you can give a look to the fastening system, which is easy and effective. But I already had some cheaper bags, actually six of them already, and I decided to modify the hook since the original one is fast but not safe at all, it bends if bags are too heavy.
Step 2: The Rack
This is my aluminium rear rack. It's a good one, sturdy and light.
First thing to do it to measure the diameter of the horizontal shaft, which is 10mm in my case. If you look carefully you will see a second smaller shaft inside the flat bed, which I used as anchorage for closed position of my hook. You will understand better in next step.
Step 3: Sketches and Plans
Usually I start with a simple concept in my mind, and I try to put it on paper. In this stage I find first obstacles, I see that some solutions are not easily practicable, and I try different ways. This time my first idea was to 3D print a new clasp, maybe with an integrated automatic hooking mechanism. But that is a long process, and lately I'm quite busy.
I opted at last for laser cut acrylic plates and this project you see here. Initially I didn't think to lock the clasp against the smaller aluminium shafts, but I understood that it was necessary to avoid the hook rotating with heavy bags.
Step 4: Prototypes
When you complete your first drawing, you can choose the material. I used a red/pink 3mm plexiglas panel which team of WeMake gave to me.
WeMake FabLab in Milan has two lasercut machines, a bigger one with 120x90 cm plane and 80W laser and one with 60x30 cm plane and 50W laser. I used the smaller one since it was enough for this project. Actually I had to set the speed to about 5 and power to 100%.
Now convert your drawing in a .dxf file and upload it on the laser machine. Set the right parameters, set the origin point, place the plexiglas plate, and start cutting the first prototype.
Step 5: Testing
Test your prototype and make a revision if needed (as you saw I needed more than one).
Since this clasp has to fit up between two aluminium pipes with a good precision, the adjustments are of the order of 0.1 mm, and you have to make them on your own rack dimensions. This is the reason for which I don't upload any project file.
Step 6: Final Version
When you are sure that clasps fit perfect on the rack, and that aluminium bars fit up in all the holes, you can copy the shape 8 times and cut everything.
Step 7: Aluminium Connections
I used 8mm diameter aluminium pipes for the main pivot, and 6mm pipes for three reinforcement bars between plates. Just measure the right length placing two plates at the side of one hook, and begin cutting four 8mm diameter pieces, and twelve 6mm diameter ones.
Step 8: Some Sanding
To refine the cuts you can sand all pieces on a small grain sand paper.
Here is the step where I have still some doubt. It really depends by the material you used, and by the play between pipes and holes, but probably beating them in the holes with an hammer will be not enough as sturdy link. You will probably need to glue pieces in place, and I still have to find the right glue. Anyway you can begin connecting all pipes to one plate of every clasp.
Step 9: The Handle
In my project the handle will also act as aid to unlock the bags from the rack. I decided to use original handles, because they are made by a good rubber. I I will ever decide to make another revision I will design two pipes to fit both holes of each end, so that leverage will be much better.
I tried to insert two plastic spacers at the handle sides, to keep it centered, but then I decided I didn't need them.
Step 10: Pivot and Hook
The pivot and the original hook need to be joined together, to avoid that we loose a bag after jumping on a bump. I could have glued the pivot to the hook, but then I could not have been able to glue the pivot to plates, so I decided to use small cable ties to obtain a double result: first I lock the pieces together letting them rotating, second I reinforce the plastic hook helping it to remain closed.
To avoid any interference between cable ties and plates, engrave with a cutter small grooves as in the pictures, where cable ties will pass and be stuck.
Step 11: Assembling Clasps
Now you can assemble all clasps placing the second plate and gluing it. Adding glue it will be a thorny process, just make some test on discarded plates and be patient.
Pay attention to the right orientation of each end of the handle. Then you should have two handles with clasps and hooks, ready to be wedged to the bags.
Step 12: All Wedged
Wedge all four original hooks in the slots on the bags. Before gluing them pay attention that slots you choose are right ones for the bag position on the rack. Sometimes you want to keep the bag further you can from your foot while pedaling, and also some slots are wrong since rack has not free space there on the shaft.
Step 13: Test It
If you can wedge your bags in place, and if everything works, it's time to glue the hooks or block them with cable ties, so that they can't exit anymore.
You can see from the picture that bags can't move in any direction when clasps are closed.
Step 14: Ready to Leave
Hook second bag and closed all clasps. Now you can fill bags with something very heavy and pedaling to look for some high bumps to test the resistance.
Step 15: Some Improvement
I'm quite happy with the result. This project has been fast and compelling. Anyway I wonder how many loops will consume the joint mechanism so that the clasps will not stay stuck anymore. Probably only time will give an answer to that. Meanwhile I'm thinking to some improvement, and maybe I will cut new plates to connect handles with both holes.