Intro: Lightbulb Knife Sharpener
Sometimes you really need to sharpen a knife. But what if all you have on hand is a burned out high pressure sodium light bulb and desperation? You're in luck! The bulb's quartz core can be used to sharpen knives, tools, and your reputation as a genius. If you've got a couple basic tools and a dowel, you can upgrade that quartz to a nice sharpener that's also a great conversation starter.
High pressure sodium bulb (burned out, unless you want a sharpener more than a working bulb)
Dowel, 1" - 2" diameter, whatever feels comfortable
Washer, same diameter as the dowel
String, flammable but slow burning
Drill press or drill
Nice but not strictly necessary:
Step 1: Break the Bulb
You have to be careful not to break the quartz core when you do this, so I decided against smashing the bulb on the ground. I tried a couple other methods and realized the bulb was much tougher than I thought. Eventually, the combination of scoring, burning, and tapping did the trick.
It helps to score a line around the bulb to guide the break. I set up a board against the dogs on my bench, clamped in a glass cutter, and braced the bulb against the board to get a straight line all the way around. I spun the bulb several times to get a nice cut.
I then tied a string around the scored line and set the string on fire. You want a string that will burn for a little while to get the glass nice and hot on that line. When the string burns off, immediately dunk the bulb in cold water. You should hear a crack from the cooling glass pulling apart.
If your bulb didn't break in half in the water, tap it gently on the edge of something. You should end up with two halves of a bulb and an exposed quartz core.
Step 2: Remove the Core
Sometimes you can just wiggle the core out once you've exposed it. If it is being stubborn, gently break off the rest of the glass so you can reach the bottom of the quartz and pull or cut it out. This is the part that makes this broken bulb into a really great knife sharpener.
Step 3: Make a Handle
Cut a dowel to the length you want your handle. You can either sand down the dowel and call it good or, if you have a lathe and a handy turning tool (see my instructable for a turning tool here), you can make a grip and some embellishments. When your handle is the shape you want it, sand and stain it.
Drill a hole in the top of the handle just barely bigger than the diameter of your quartz.
Step 4: Put It All Together
Use epoxy to secure your quartz in the handle and glue a washer on the top of the handle.
And you're done! You've got a quality knife sharpener made on the cheap from a burned out bulb and a dowel. Time to make all of your knives much sharper.