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. YOUR SHOP
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Changing the belt position alters the rotation speed of this drill press. Most hand drills have a variable-speed function to control rotation. Photo by Scott Nesbitt |
Know the drill
Editor’s note: From time to time, GCM presents articles from its archives that are timelessly helpful for its readers. This article was originally published in January 2006.
When boring holes, pay attention to four factors, and you’ll work faster and get cleaner, straighter holes; your bits will stay sharp longer and break less often. Each factor changes depending on the material you’re boring and the kind of bit you’re using.
Speed. The bigger the bit, the slower the speed. This comes from the rules of materials and the laws of geometry. A drill bit is harder than the material being bored. Rotate the tip too fast, and it skates over the surface or bounces around, producing a bunch of little chips. The tip and cutting edge can easily overheat from friction or develop chips from the bouncing. Carbide-tip masonry bits are designed to bounce; all other bits produce a nice, smooth cut and a long, clean chip when cutting metals or other solids. In wood or other grainy material, you should produce chips, not dust.
Here’s the geometry: Keep the speed of the outer edge of the cutting surface at or below its ideal cutting speed. With each rotation of the drill, that outer edge travels a certain distance. The formula is: C = D × π, where C is circumference, D is diameter and π is the math constant 3.1416. The outer edge of a 1-inch bit travels exactly twice as fast as the edge of a ½-inch bit, so wider bits must be rotated more slowly than narrower bits.
Pressure. To keep the bit slicing, you need to apply pressure. Too much pressure jams the bit; too little lets it skate. Each bit and material has an ideal pressure in pounds per square inch; increasing the bit size requires increasing the pressure. Harder material will require more pressure. Since you probably don’t have a computerized drill press, your best bet is to pay attention to the chips coming out of the hole and adjust your pressure to produce a nice steady flow of long thin chips.
Stability. A drill press keeps the bit running straight into the hole and lets you apply lots of pressure. Even the thinnest bits rarely break in a drill press. But drill bits are hard steel, and hard steel is brittle. Stability is why professional-grade hand drills have an optional side handle that lets you get a solid, two-handed grip on the tool. If possible, you should always grip a hand drill with two hands. Use your upper body and shoulders to apply guidance and pressure rather than your wrists and elbows.
Lubrication. Liquid is applied for two reasons: to carry heat away from the cutting tool and to lubricate the metal-to-metal contact point where the tool touches the base material. So should you add lubricant every time you bore a hole? Here are some suggestions:
Steel. Add oil or grease
Brass. Drill bit makers generally say keep it dry
Aluminum. Light oil or light grease
Copper. Try grease, lard or (undiluted) dishwashing detergent
Plastics and other synthetics. Water, dish soap or a wax stick
Wood. Grease or heavy oil (for outdoor items); dry spray or wax stick lube (for decorative items)
Starting Feb. 1, 2009, employers were required to begin posting a summary of the total number of job-related injuries and illnesses that occurred last year. Employers are only required to post the summary — OSHA Form 300A, not the OSHA 300 Log — from Feb. 1 through April 30, 2009. To obtain a copy of OSHA Forms 300, 300A and 301, visit the OSHA Recordkeeping Web site at www.osha.gov/recordkeeping/index.html. Some hidden dangers may lurk in mechanics’ working areas when working with compressed air in a maintenance shop, according to an article in The Newsletter by Ron Smith, CPSI. To counter the dangers, he suggests taking these safety precautions: |
