SoC wrote on 11/19/17 at 18:54:58:First the aluminum stock from the hardware store is pretty soft alloy, in picture it looks anodized, which is usually softer material. It experiences a lot of fatigue when bent. How did you bend it? In a break or possibly in a vise. Third did the bend involve a mallet? and forth was it a clean one shot to the correct angle or did it involve any bendies to get it at the right angle. Its always best to use a break and get angles correct with aluminum in one clean bend. If in a vise and hit with a mallet it fatigues the metal additionally. If it involved any tweaking bending to get angle correct that causes a lot of fatigue. There is a little science to bending aluminum, there are radius considerations, known as the minimal bend radius, which can be referenced on line. Also like mentioned with tweaking, you can bend aluminum, but can't straigten it if bent to far, that's why it's best to use a break.
That said, to be honest I would have felt safe in using a similar material for that application, maybe just shortened to height of the arms.
Hey SoC, thanks for the tips
To answer your questions, I tried a few different methods of bending the aluminium.
1. I put it in a vice and yanked it - snapped right off.
2. I put it in a vice and tapped it with a hammer - ended up obviously weak.
3. I held it by hand over the corner of the anvil-flat on my vice and peened it with a hammer, kind of working the radius as I went. I was careful not to go too far, so I didn't need to bend it back out at all.
The last method seemed to produce a good result. It withstood a moderate test of putting some pressure on it by hand. I thought it was pretty good, and went with that.
I was surprised after a few months when one arm fell off! I was especially surprised by the intact one. It showed no signs of fatigue, but it broke off with the slightest pressure.
I've now mounted the signals in the fender-rail holes to keep me on the road. I was going to make a new bracket from mild steel, and weld instead of bend. But, I kind of like them where they are now, so I'm re-thinking the setup. I want to add some kind of capacity to carry a small bag on the back, even if I carry a passenger. I'm thinking about a custom made sissy bar - I just don't like the stock fender-rails which the OEM sissy bar attaches to. I'm not in a hurry so I'll take some time to think, sketch, and prototype. A friend of mine knows a guy that does that kind of custom work, so I'll probably pay him a visit eventually.
In the mean time, I'm waiting for my Triumph Superbars to arrive for the other end of the bike!!