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07 November 2003

Options for Drilling Holes in Glass

Excerpted from Instruments of Amplification. Fun with Homemade Tubes, Transistors, and More by H. P. Friedrichs.

A classic, tried-and-true method appears in numerous laboratory texts. In the old days, a piece of brass or copper tubing, slightly smaller in diameter than the desired hole, was chucked into a drill press. The end of the tube was nicked with a sharp blade, and embedded with carborundum or silicon carbide grit. Drilling was really a grinding operation. The improvised bit was rotated against the glass, while a slurry of water and abrasive was dribbled onto the work area. A small wax or putty dam was sometimes fashioned to pool the cutting fluids around the drill site. I experimented briefly with this process and found it both frustrating and time consuming.

Recently, tool manufacturers have introduced special purpose drill bits intended for working glass, ceramics, and other , exceptionally hard materials. These bits have the appearance of a bullet-shaped paddle, welded to a steel shaft of shank. They're fairly expensive at five or six dollars apiece, but they work very well and are much faster than traditional drilling methods. Happily, these bits can now be found in many hardware stores and home-improvement centers.

Let me share with you three tips for their successful use: First, the bits can probably be used in a hand drill, but I strongly recommend a drill press. Glass is a brittle and unforgiving material. the drill press allows for more precise control of the bit. Second, use the slowest speed possible. Higher speeds will simply heat and burn up the bit. Finally, I like to dip a light grade of machine oil on the bit as I drill. I've found that the bit seems to cut better, it remains cool, and the oil controls the glass dust produced by the drilling operation. By the way, make sure you're wearing safety goggles and a dust mask.