Selecting Blades and Bits

All things being equal, having good-quality power tools is only half of a winning formula for getting maximum productivity throughout the day; the other major factor is furnishing those tools with top-quality blades and bits, and the right selection, at that. Some of the most popular accessories among electricians are step bits, hole saws, reciprocating saw blades, and dry-cut metal saw blades, as well as ship auger bits, spade bits, and drill bits. Manufacturer mentions are noninclusive. Step bits Step bits, which fit into standard electric drill chucks, save time and effort because they allow users to automatically size holes in metal and other thin materials, including plastic or wood, without having to change bits all along the way. They are well suited for drilling knockouts in electrical junction boxes and cabinets, and for drilling into lighting fixtures. Shaped like mini evergreen trees with stepped graduations, these bits provide round holes in any of several sizes, generally from 1/8 to 1 inch. While some step bits require pilot holes, most don’t. The electrician drills continuously until reaching the desired diameter. The user can often feel when the bit pops through; some bits also give off an audible “pop.” Some models have the increments etched into the flute areas. Step drill bits are single fluted or double fluted (which may create a more triangular rather than pure round hole but could do it faster than a single-fluted model). With single-fluted step drills that produce very clean holes, deburring is typically unnecessary. Minimum and maximum hole sizes and step increments vary within and among manufacturers. Klein Tools, for example, offers a full line of Klein-Unibit Step-Drill Bits, single-fluted bits fabricated of high-speed steel in sizes to fit 1/4-inch, 3/4-inch or 1/2-inch chucks of portable electric drills, with the largest bit featuring 13 increments. The single-flute design, points out Steve Gianaris, Klein Tools product manager, eliminates skidding, ensures penetration of softer materials at the proper speed, and helps eliminate vibration and chatter. The bits are available in fractional, metric, and TiN coated, with the sizes laser-etched in the flute. With a black oxide coating, the flutes trap oil and prevent rust, keeping the bit running a little cooler and further extending the life of the bit, Gianaris noted. MAGNA Professional Tools double fluted Drill Tree Bits, available in high-speed steel and in titanium nitride (which, the company notes, requires 25 percent less effort and lasts up to six times longer), feature self-starting points for easier drilling. Various models are available, including one in each material that can make 13 different-sized holes. Gardner Bender step bits, with self-starting, self-centering drill tip, are designed to drill through 10-gauge mild steel or stainless steel. The bits feature a three-lobed shank for positive non-slip grip in drill chucks. Milwaukee Electric Tool Corp., Makita USA, and Hilti each also manufacture double fluted high-speed steel step bits with self-starting tips in varying drilling ranges. Hole saws For efficient drilling of large (generally 1 inch or more) holes, hole saws used with electric drills could come in very handy. Hole saws may have polished or coated bits, which last longer on harder materials. To ensure a particular hole saw is suitable for use on metal, look for a model that specifies that capability. The Milwaukee Bi-Metal Hole Saw, available in over 40 different configurations for a variety of hole diameter sizes and depths of cuts, features a heavy-duty thick back design that reinforces the rear stress points and helps assure continued straight cuts over time, notes Dave Tatem, director, accessory business at Milwaukee. The saw, capable of cutting into all types of machinable materials, including steel, is made of cobalt steel and features a bi-metal tooth construction that, according to Tatem, adds to tool longevity. Klein Tools Journeyman’s Hole-Saw Set contains the 13 sizes most commonly used for electrical applications in steel and other metals as well as wood and plastic. The saws feature a thick-cup design which, says the company, provides more strength and longer-lasting cutting performance and eliminates pilot-hole elongation that results in excessive vibration and chatter. Slanted knock-out slots in the sides allow easy core removal. DeWALT Industrial Tool Co. bi-metal hole saws are designed for heavy-duty cutting in standard or deep-cut applications in steel and other metals as well as wood, plastic, and other compositions. They are available in various size hole diameters, from 5/8 to 6 inches. Makita Carbide Tipped Hole Cutters, which can be used either with a cobalt-center bit suitable for cutting sheets of stainless steel, galvanized iron, and aluminum, or a carbide center bit tipped with tungsten carbide, which is suitable for drilling many materials, feature a built-in stopper that prevents the cutter from penetrating further. Recip blades Matching a recip blade to the application maximizes productivity, with width (up to 1 inch), thickness, and length of blade, type and number of teeth, and blade material all contributing factors. Thicker blades are generally more rigid and, therefore, more likely to hold up well under rigorous use. Blade thickness traditionally has been 7/200 inch; some manufacturers are now offering blades up to 31/500-inch thick. Bi-metal blades generally last much longer than carbon steel blades. Progressive blades typically feature fine teeth close to the shank and coarser or bigger teeth toward the tip. At 31/500 inch, The AX, from Milwaukee, available in 6-, 9-, and 12-inch length blades, is well-suited to rough-in work and to cutting into wood as well as nail-embedded wood without bending of blades, notes the manufacturer. Milwaukee also offers the TORCH, a moderately heavy (21/500) fine-tooth blade appropriate for metal cutting, with teeth range from 10 TPI to 18 TPI, and sporting a relatively thick back that, says the company, increases rigidity and enables the tool to cut squarer cuts. In their new Progressor line of recip blades, BOSCH offers three progressive 21/500-inch entries—one for metal, another for wood, and a third, 8-inch-long universal blade designed to perform well in a mix of materials, including wood with nails. The number of teeth per inch varies across the length of the blade, which, notes Ron Techter, business manager for accessories at BOSCH, allows for fast cutting through a mix of materials as well as various thicknesses of material. The blades are individually cut out of a band of steel, rather than stamped from bands of steel, which helps ensure consistent front teeth important for plunge cutting as well as fast cutting. Makita offers several Industrial Range recip saw blades, including its new line of Demolisher blades, suitable for nail-embedded wood and other materials, which are 31/500 inch thick and 7/8 inch wide and have taper-back blades. Each features a first tooth consistently centered on the blade for straight plunge cuts. The company also offers a full line of wood-cutting, all-purpose, and drywall and plaster blades, a couple of which are progressive. MAGNA offers several Bi-Metal Universal Shank recip saw blades featuring a flexible spring steel back that, notes the manufacturer, helps ensure long blade life. The company also sells demolition, progressive tooth, and metal cutting universal shank recip blades, among others. Dry-cut saw blades New, fast-cutting, long-lasting dry-cut blades for dry-cut saws essentially replace abrasive blades for metal cutting, including conduit and angle iron. The blades cut, rather than grind down, the material, leaving a clean, burr-free, finish without creating dust. According to Brent Withey, Makita accessories manager, it is possible to get up to 2,500 cuts with a carbide-tipped dry-cut blade, compared to 50 cuts with an abrasive blade. Makita recently introduced four 12-inch diameter carbide-tipped dry-cut blades—one for ferrous metals, a second for ferrous metal that lasts twice as long and provides quieter cutting, a third for stainless steel, and a fourth for thin ferrous metal—that are first hand hammered and then machine hammered. Tenryu America, Inc. offers dry-cut blades with 14-inch diameters in two different models: the standard single-plated, slot-less Steel Pro, made of heat-hardened tool steel saw plates with impact-resistant-grade carbide teeth implanted and braze welded into a tooth pocket, and the similarly toothed and welded Stealth, which is double plated, with the two plates spot-laminated together for reduction of vibration and quieter cutting. The blades on both models feature a modified triple chip grind pattern, with alternate teeth chamfered on both sides to 45 degrees, with flat teeth in between. DeWALT’s triple-tooth 14-inch diameter dry-cut blade sports a universal 1-inch round arbor and carbide formulated teeth with 12 percent titanium, which, the manufacturer notes, contributes to long life. Porter Cable has a new 14-inch, 72-tooth metal cutting dry cut blade consisting of two plates bonded together. This design, notes the company, creates a barrier to noise and vibration. Self-feed bits Self-feed bits, useful for boring conduit holes in wood, feature screw tips in the center that effectively pull the bits into the work (helpful when drilling overhead) and cut quickly without leaving a big wood plug in the middle, rather, the chips are thrown out behind the blade (helpful when going through double plates). Bosch, Milwaukee, and Makita manufacture them; both Bosch and Milwaukee offer quick-change 7/16-inch hexes on their bits to accommodate larger drills. Specialty wood bit Milwaukee PathFinder drill bit, introduced earlier this year, drills curved or irregular holes up to 90 degrees. The innovative bit, available in eight sizes, bores straight holes in wood, composites, chipboard, plasterboard, and hard plastics two to three times faster than traditional spade bits and almost as clean as a forstner bit, notes Tatem, eliminating the blinding and vibration associated with other drill bits. The bit, which has six cutting surfaces on the front, side, and back, cuts precise channels and grooves for recessing wire, conduit or pipe and drills quickly in-between studs for running wire and conduit. The FELDMANS provide Web content for companies and write for magazines, trade associations, building product manufacturers, and other companies on a broad range of topics. They can be reached at or (914) 238-6272.

Stay Informed Join our Newsletter

Having trouble finding time to sit down with the latest issue of
ELECTRICAL CONTRACTOR? Don't worry, we'll come to you.