A while ago, I got a set of three foam padded glasses on ebay for a great price. I use the yellow tinted ones while hiking, the standard black tinted ones while bike riding, and these clear ones worked great as safety glasses when I was machining something. The foam around the lens helps to keep out dust and other debris.
However, repeatedly moving the glasses from eyes to my forehead eventually snapped them in half. I had previously fixed one of the broken ear pieces with a bit of super glue, but the same method did not work to repair the broken frame. Since there wasn't enough room for tape, and I'm too cool for that jazz anyway, I glued a pair of strong permanent magnets to the frame to connect them together and replaced the ear pieces with an elastic strap. The glasses can now be put on by pulling the strap around the back of my head and bringing the two lens near each other. The magnets do the rest of the work...
Step 1: Necessary Parts
Since every situation is a bit unique, I will list what I used and why so you can decide what would work best for you.
Safety Glasses - They don't need to be broken, but then this would be kind of pointless.
2 Small, Strong Magnets - These are used to easily connect/disconnect the two frame pieces.
Elastic Strap - I got this by cutting the unnecessary over-the-head strap from a common headlamp. Using the strap is easier than standard ear pieces because of the front magnet design.
2 Small Open Slit Rings - This kind of like those small cheap rings that attach a keyless remote to your key ring.
Needle and Thread - I needed to sew the elastic strap back to itself to make a loop for the metal rings.
Precision Phillips Head Screwdriver - The screws that hold the earpieces to the glasses frame are tiny!
Needle Nose Pliers - Used to Reshape the metal rings into Ovals.
Soldering Iron - Used to seal the slit in the metal ring
Super Glue - To connect the magnets to the frame.
Step 2: Remove the Ear Pieces
There will be a very small screw used to hold the ear pieces to the front part of the frame. These can be easily removed with the right screwdriver.
Step 3: Preparing the Metal Rings
The rings are OK to use, but I wanted to flatten them into more of an oval so they fit better. This can be done with a pair of pliers.
Step 4: Attaching the Strap
One end of the strap had an adjustable loop in it. I had to make a loop in the other end by folding over a bit of the strap and sewing it to itself. Once both sides have some kind of loop, the metal 'ovals' can be attached to the strap.
The metal 'ovals' can then be run through the screw hole in the eye glass frame. This was the best way I could come up with attaching the strap to the frame.
Step 5: Sealing the Rings
Once the strap and eye glass frame are connected, the metal rings can be sealed so they don't come apart. This can be easily done with a tiny bit of hot solder.
Step 6: Attaching the Magnets
Finally, the magnets can be put in place with a drop or two of super glue. Make sure to hold the magnet in place long enough for the glue to set. Also, ensure the correct side of the second magnet you glue is is facing out so the two will attract each other instead of repel.
You may need to sand the broken area down before adding the magnets if they aren't straight.
Step 7: Keep Those Eyes Safe
When the glue is finally dry, give these glasses (now more like goggles) a try. I just wrap the strap around the back of my head, bring the two broken pieces near each other, and let go. The magnets do the rest of the work.
As a final note, my wife says these are still super dorky... but way better than taping them back together.