I'm blind as a bat. When I got my last pair of glasses I opted for the version that has the sunglasses attachment that mounts magnetically. Over my time of wearing them there have been times when I 've needed to take them off, but not had time to put them away (e.g. driving into a parking garage). I would either put them in my lap or the cup holder. Not only did this risk scratching them, but invariably they go flying if I have to break hard. I decided to take advantage of the magnet already in them to solve this problem.
Step 1: Tools and Materials
*A rod or other suitably shaped piece of ferrous material
*A cotton ball
*Dremel w/ cut off wheel (or other implemtns of metal cutting and shaping)
*Bench vise or other way to hold your work piece.
Step 2: Choose and Cut Your Metal
I chose this particular rod as it had a flat area on the end that would allow the magnet in my sunglasses to make the most contact with it. (It also has a threaed hole in it that will be handy later.) If your metal doesn't have a convienent flat area I'm sure you can make one. I believe it can be done by applying the techniques I describe for cleaning up the rough end in step three to the face of the work piece.
I then used my dremel to cut most of the way through the rod about 3/4 of an inch from the tip. I cut from both sides leaving a thin piece of metal connecting the end to the rest of the rod. Then I used a pair of pliers to break the end off the rod. (I've found that if I cut all the way through the rod the piece I want goes flying across the room. You then spend more time looking for the piece than it actually takes to do the project. Or you're trying to call 911 with a piece of metal in your eye.)
Step 3: Clean Up the Rough End
When you've finished cutting your material there will be a rough end. In order to properly mount your sunglasses holder this end will have to be leveled off. I did this by mounting my dremel sideways in the dremel drill press. (If you don't have this nifty thing you can build one by following Zanshin's rotary tool wood slab instructable). I just held the rough end of the piece to the flat of the cutting wheel. This leveled it nicley.
You can use a pair of pliers to hold the piece, however I took advantage of the anatomy of my work piece to control it. I screwed a threaded rod into the hole on my work piece. This gave me a handle to manipulate the piece and keep my hands from getting burned as the metal heated from friction.
Step 4: Mounting
Now grab your newly fabricated sunglasses holder, isopropyl alcohol, a cotton ball and your superglue and go to the car to which you intend to mount the holder. Sit in the drivers seat and think about where you want the mount to be. You want it to be within reach, but not in a place that is in the way of your controls or where you'll bump the sunglasses.
Once you've selected your spot put some isopropyl alcohol on the cotton ball and clean the area (I have to thank Zach for this tip in his Garmin Nuvi Mount instructable). Once the residual alcohol has evaporated, put super glue (If you want to be able to remove it w/o damaging the surface choose something else to secure it) on the bottom of the holder. Put the holder in the proper orientation and place it in the spot you've cleaned. If the holder is likely to fall before the glue dries hold it in place or rig a jig of some sort to hold it in place.
Once the glue has set up apply sunglasses.