I built this custom bracket for my 1979 Triumph Bonneville. Its construction require a fair bit of tooling that you may or may not have access to, but it didn't take much time, and certainly not much in materials to produce. This particular instructable is not so much to provide a "how-to," but rather the inspiration for your own creation. Having built this one, I would do it slightly differently, as I'm sure you will too.
Step 1: Tools & Materials
I have access to a fairly complete shop, but perhaps you do not. Feel free to make do with what you have, innovate and experiment. Do not let the limitations of your tools dictate the directions you take.
Hydraulic sheet metal brake
Sheet metal finger brake
Custom-made flaring die
16ga cold rolled sheet steel
Aluminum Round Bar, ~ø3/4"
ø1/2" mild-steel (1018) round bar,
1/4-20 nuts and screws (4ea)
Step 2: Conceptualization and Layout
I needed a new license plate bracket. I didn't want to spend much in terms of time, effort of cash. I knew I wanted something simple, stylish and lightweight. I used a bit of 16 gauge I had lying around. Though I ended up folding the short edges, in retrospect, it would have been better to fold the long edges. Nevertheless, it's plenty sturdy for a license plate.
I cut the sheet steel slightly wider than the license plate, and the same height. Then, I traced the holes using a Sharpie®. I also roughly sketched where the mounting holes for the bracket would go, and where the lightening (Speed®) holes would go. After I was pleased with the sketch, I measured the holes accurately, and drilled the holes. When drilling a hole in sheet metal greater than ø1/4", I prefer to use a step-bit, or as my friend Conor calls them, a "christmas-tree-bit". They are much safer, especially when drilling larger holes, as they have less propensity to grab and spin the part you're working on. Plus, they have the added benefit of putting a sweet chamfer on the hole. You can deburr the backside of the hole (which almost always has a gnarly burr) with the same bit, just go slow.
Step 3: Flaring/Dimple Dies
Depending on who you ask, these dies are called either dimple dies or flaring dies. I prefer flaring dies myself. I made this one a few years back. It's designed for 3/4" holes, though it may work on other sizes. It's made from 4140 steel, and is not heat treated. I've flared both mild steel and aluminum, perhaps 100 holes and it shows no wear. The flaring die can be used in a vice, an arbor press a hydraulic press or even a largish C-clamp.
After flaring the larger holes, I realized the screws that secure the bracket to the rear fender would interfere with the license plate lying flat on the bracket. I quickly drilled, tapped and countersunk a piece of steel 1/2" round bar. I first applied a bit of grease on the threads and tapered surface of a flat head screw, then I gripped the round bar in a vice, passed the flat head screw through the 1/4" hole drilled in the bracket, and threaded the screw into the round bar. Using an impact driver (Milwaukee M12), I tightened the screw into the round bar whilst I head onto the bracket with a gloved hand. While not perfect solution, the flathead screws now sit much closer to the surface of the bracket, and no longer interfere with the license plate.
Step 4: Welded Nuts
While nuts and bolts would have worked fine, I wanted a cleaner, more permanent solution. Thus, I threaded four 1/4-20 hex nuts onto a piece of all-thread, then turned them round on a lathe. You can grind them round as well if you don't have a lathe. Simply stack the nuts on short piece of all-thread and tighten together. Then, grip the all-thread in a drill and spin it as you apply it to a grinding wheel, sanding disc, or sanding belt. Use caution when using this technique, as it can be dangerous for the inexperienced. If you're not confident, hex nuts look good too!
Using an old license plate as a template, I bolted it to the bracket and tacked the nuts with the TIG welder. Note the use of brass screws. For this job, I used stainless nuts. If you use stainless bolts and stainless nuts, the heat from the weld will cause them to fuse together just a tiny bit. Then, when you try to remove the bolts, the stainless will instantly gall and you won't get the two apart. By using dissimilar metals, you can avoid this all together. Also note the use of silicon bronze filler rod. By using it, you can keep the heat low (the base metals don't actually melt), and thereby minimize any distortion in the sheet metal. Silicon bronze is surprisingly strong (certainly enough for this application), and it's very easy to work with.
Step 5: Installation on the Fender
Next, I drilled the holes in the fender. The lower hole I slotted slightly with a round file. This gives me slight adjustability so I can square up the bracket with the bike.
I turned a pair of aluminum spacers, just because I like the almost hidden details. Alternatively, you can use a pair of plastic washers available from the hardware store.
And that's it! All that needed is a layer of powder coat, but that will come later.