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.