Each Sunday for seven weeks, we will be posting a different part of our series "How to use a flex shaft"
What can you do with burs? Grind, carve, excavate, enlarge, trim, fit, adjust, mill, set stones, create texture, make catches, and fill teeth. (You didn’t think Dr. Fillgood was actually using drills, did you?) Steel burs can cut metal, wax, wood, plastics, and composites. The easier question might be: What can’t you do with burs? I often reach for a bur before I grab a file. But I’m getting ahead of myself.
Let’s start with basics. Is it “bur” or “burr”? I’ve seen it both ways, but “bur” is the most common. (Confusingly, burs are sometimes used to remove “burrs,” the ragged bit of metal left around a drilled hole.)
I think of burs this way: Wrap a file around a shaft or shank, and you have a spinning file — a bur. And, as with a file, getting the contour that you want in your work depends on the shape of bur you choose. The most common shank diameter for burs is — you guessed it — 3⁄32 in. (2.3 mm). They’re available individually, in sets of graduated sizes or different shapes, or in same-sized six-packs. As with drills, lubrication can make a dull bur seem sharp again. Use the same lube that you would for drills. Finally, remember that most burs won’t cut in reverse.
Burs are available in tungsten vanadium steel (tungsten), high-speed tool steel (HSS), diamond, and carbide. Tungsten and HSS are widely available and form the backbone of catalog burs, while carbide is hard and brittle and is the least commonly used. The harder and more heat-resistant HSS will generally hold up longer, but tungsten burs offer a wider selection of profiles (shapes). There are tungsten options that are designed to prolong life: specially hardened “Blackhead” tungsten burs, and tungsten burs coated in yellow titanium nitride.
Tungsten burs are machine cut, and so are consistent in diameter and tooth angle. HSS burs are all cut by hand by tiny men using diamond grinding wheels and jigs, so they vary a bit (only kidding about the little folk, but the burs are hand-cut). The teeth on HSS burs are usually cut in arcs radiating from the center as opposed to the straighter ones on their tungsten cousins. Generally, tungsten vanadium burs are about one-third the cost of HSS burs and are commonly available in six-packs. HSS burs can be resharpened, although they will come back a bit smaller.
HSS: Spearhead, Elite
Tungsten vanadium: Busch, Braessler, Fox, Dentsply Maillefer, Lynx
Brands carried by vendors will vary, but an extensive selection of styles can be found in most catalogs.
Unlike files, there are only two cuts (tooth size) of burs: “fine” and “standard.” But, like files, burs come in single cut or crosscut. The latter cuts much faster, and leaves a cleaner cut. Not all shapes are available in crosscut. HSS crosscut burs aren’t fully crosscut, but do have several crosscut lines in them to help evacuate material.
Profile is key. I use one shape for a multitude of tasks by using different parts of the bur: the side, the tip, or the edge. And I may use several shapes in progression to get the result I want. Here’s a few profiles that I use, plucked from the multitude: