So I've just gotten an awesome new bike from Public, and love it to death. Cycling to work is so much less stressful than driving, and I love the classic city look of the bike. So when I wanted to add a pannier to carry stuff around, the panniers that I had for my other bikes worked, but didn't really fit in with the look of the bike. I came across this leather briefcase that my Dad bought in the 60s, and I thought this would be the perfect thing to convert to a pannier, and would suit the classic look of the bike perfectly. You could do the same thing with any vintage briefcase or even a small suitcase you'd find at your local thrift shop.
Step 1: Get Some Clips
So I was lucky - one of the panniers I had was made by Karrimor and it had clips which attached onto the bike rack which were adjustable (and locked into place). Because they were adjustable, all I had to do was to remove them from the pannier frame with some screws and they could be attached to something else.
Plan B was to remove the rack clips from an existing pannier by drilling out the rivets which typically hold them together. From the other panniers I have, it looks like drilling the rivets from the inside of the pannier, using a drill bit which is slightly larger than the inside of the rivet would be the easiest way to do it.
In either case, once you have the rack clips, you are ready to move on to the next step.
Step 2: Place the Clips
Once the clips are free from their original panniers, the next step was to place them on the rack to get some sense of how wide to space them. Basically the idea was to space them wide enough that the are stable, but to also allow them to move back and forth a little bit if you need to adjust the position of the bag.The image shows where I thought was the best spacing. Then measure the distance between the centre of the mounting holes.
Step 3: Create Some Internal Support
The other panniers that I had all had a hard piece of material on the inner surface of the bag to provide some structure and to take the stress of the bag material. While the leather of the bag was pretty thick and sturdy, I thought it was still a good idea to have something internal to help take some of the strain, so I found a piece of 1/8" ABS which I cut a 3" strip off of. Then (not shown) I drew a line through the middle of the piece and made two marks the width of the clips centered on the plastic.
Assemble your fasteners, basically find some nuts and bolts and washers that are long enough to go through the clip, the bag, and the support strip. Once you know the size of the bolt you need to use, drill the two holes in the support strip.
Step 4: Locate the Holes in the Briefcase
The next step is to find where to make the holes in the briefcase. You can use the support strip with the holes in it as a template for horizontal spacing, so all you really need to find is the vertical location. To do this, I simply held the the briefcase in position with the clips on the rack and eyeballed it from the end. The idea was to have it sit on the rack so that when the handle is folded over it lies flat on top of the rack. Once I had that in position I used a piece of masking tape to mark the vertical place on the edge of the briefcase - I figured if it was out a few mm it wouldn't really affect anything.
Once I had that measurement, I put a piece of tape level across the back of the briefcase and using the support strip as a template marked the two holes on the tape. Use an awl to punch holes through the leather. I also drilled out the hole using a drill bit one size smaller than the hole through the support template. I'm not 100% sure you need to do that, but once you start to twist the bolt through the leather, the undersize hole starts to get threaded, and I figured that would help keep water out etc.
Step 5: Assemble the Clips
Now it's simply a matter of putting everything together. Once you have everything bolted together it's probably a good idea to ensure it doesn't work loose - I used 2 nuts on the inside, or you could use a lock washer, or some Loctite etc. And of course you can spend some time finishing edges and grinding down the end of the bolts so you can't snag anything when you put your stuff in and out of the briefcase.
Now, off the bike these things aren't the prettiest clips ever - maybe next time I'd look into using some metal ones that match the bag a little better but these clips were handy. One thing I noticed was that it's not important whether the clips move or not -since there is only one bolt per clip for these ones, ,they have a tendency to spin around a bit off the bike, even when the bolts are tight. Originally this frustrated me until I realized that it actually makes them less likely to snag on things because they can move around. Overall, I had no problems carrying the case around off of the bike, the only thing you may want to consider is how the clips look with your case. Some leather covered steel clips would be sweet on and off the bike.... maybe a future instructable...
Step 6: Ready to Ride!
Clip your bag onto your rack and you are ready to ride! Initially I was concerned about not having anything to secure the bottom of the briefcase to the rack, but there are a couple of things that seem to work in it's favour : 1) the triangular shape of the briefcase naturally seems to press it into the frame to keep it stable and 2) Since it's made of leather, any time it does get jostled around and bang against the rack it gets dampened quite well, even with a heavy load in it. I don't know if you'd get the same results if you used a hard case type briefcase, but for now I'm going to keep using it without any kind of restraining mechanism on the bottom.
So it's only been a few days since I've started commuting with the new bag and I love it. I'm surprised how stable it is even without an attachment at the bottom, but a large part of that could be the fact that the clips have a locking mechanism that keeps everything nice and secure. Hit your local thrift or vintage store and if you find a great bag and convert it let me know how it goes!