How to use a flex shaft: Part 6 of 7

Each Sunday for seven weeks, we will be posting a different part of our series "How to use a flex shaft"

• Part 1: Flex shaft fundamentals
• Part 2: Handpieces and foot controls
• Part 3: Drilling
• Part 4: Abrasives and grinders
• Part 5: Finishing and polishing
• Part 6: Burs
• Part 7: Odds and ends

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.

MATERIALS

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. 

BRANDS

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.

CUT

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. 

SHAPES

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:

Round, or ball, burs

The ball is the “cockroach” of burs (I’m tired of writing “workhorse”). It’s the ultimate generalist. I use ball burs from 15 mm down to 0.4 mm for a variety of tasks. The sizes that I use most often I buy in six-packs, usually tungsten vanadium, but I do have several gradu-ated sets of HSS ball burs. 

At my bench, a big ball bur is essential for trimming edges or grinding contours. I use the equator of the bur for that. The tiniest ball burs work great for signing and hallmarking work. I rarely use the very tip of a ball bur, instead using the top/side of the ball. (Normally, I hold the shank at a roughly 45˚ angle to the work.) Use them for any sort of countersinking application, for grinding round-bottomed seats for pearls, and for texturing. Grind fairly deep, overlapping divots for a peened effect. Tungsten ball burs range up to 15 mm.

Bud and flame burs

Technically, flame burs are longer and more gently tapered than buds, but they’re pretty much the same shape. A cousin to the ball, the bud bur is great for countersinking (use the tip), relieving, and general grinding (use the sides). It’s handy for stone setting, too. Some jewelers use it to grind tapered seats for flush sets. I’ve used its elongated, rounded side to prong- or tube/bezel-set deep-bellied “native cut” faceted stones. After defining the seat with a setting bur, I follow with the bud, which grinds away material for the  bulbous pavilion.

Cylinder burs

Next to the ball, I most often use a variety of cylinder burs: tapered cylinders, square (straight), crosscut, and single cut. Both the sides and tip of the cylinder have teeth. Tungsten vanadium cylinders range in size from roughly 0.6 mm to 3 mm, while HSS range up to 11 mm whoppers. I use cylinders when I want to make a groove, to extend or widen a hole, to carve clasps, or to trim straight-walled areas like bezels. 

If I were soldering a wire at a right angle to the edge of a sheet, I might grind a little depression in the sheet edge with a cylinder bur to form a seat for the wire. I mostly use the sides of the bur.

Krause bur

The long, tapered Krause is kind of like a cross between a cylinder and a flame bur. The tip sees most of the work; it’s perfect for cleaning up filigree, getting into the corner of a square hole or bezel, or refining the chevron of a marquise setting — anyplace that requires an agile little grinding point. Cylinder and Krause burs have an Achilles’ neck: The point where the cutting head meets the shank can be narrow and delicate, and since these burs are often used with lateral/side pressure, the heads can snap off. (That makes this a good time to remind you to wear safety glasses when using the flex shaft!) Consider it a refining bur.

Hart/bearing cutter burs

These look like the pavilions of two faceted stones glued girdle to girdle, or maybe a flying saucer with a sharp equator, or a squat baseball diamond. They are used in stone setting: prong, multiple shared prong, flush, channel, even bead and bright cut. The edge (sharp equator) is used. 

This bur is really about manipulation. Apply the spinning bur to a sheet of metal, and you have a notch. Drag that spinning bur, and the notch becomes a channel. Move the bur along a curved line in a piece of sheet, and that channel becomes a carved score that will allow the metal to fold with a crisp edge. I use it a lot for texturing, especially flat bands or the rim of a brooch: If you drag the bur in parallel lines, it yields a pattern like a sharp forging hammer. It can also make crosshatched lines.

Setting burs

In profile, these burs echo the pavilion of faceted stones. Like a pavilion, the front half of the setting bur comes to a point.  Where the girdle and then the crown would be on the stone, the setting bur continues up to a flat/vertical side. Many stone setters prefer tungsten vanadium setting burs: They are uniform, fairly tough, and less expensive. 

Setting burs are used in all types of faceted stone setting. Some jewelers and setters manipulate a small bur, grinding a seat into each prong (some even use hart burs this way) or slowly grinding a seat into the wall of a heavy bezel, believing that this offers the best control. (These bezels would be thick sterling, gold, plati-num, etc., rather than a thin, fine-silver bezel strip.) For round stones, other setters use a setting bur just a hair smaller than the diameter of the stone and grind the entire bezel or all the prongs at once. A smaller bur compensates for the slight wobble that all handpieces have, which has the effect of grinding a larger seat.

Even though I set fewer stones these days, I use setting burs all the time. The sloped and pointed portion makes beautiful countersinks — great for relieving and refining a hole on the inside of a ring. The vertical/straight sides can be generous in width, and I use these to grind sides and edges or an inside seam of a ring where it was sized or soldered.

Cup, or concave cutter, bur

Prepare to wince: My cup runneth over with uses for this bur. Well, maybe not runneth over, but it is a handy little animal. It’s basically a cup lined with teeth that cut and burnish. I believe that these burs were designed for rounding and finishing the tips on prongs (although a rounded prong is not always preferable). You can use them for rounding and refining the tip of any wire, especially ear wires. They’re also useful for finishing rivet heads. I gently manipulate the handpiece in a circle to help the cup create a domed rivet. 

The art with these burs is in selecting the proper size. Too small, and it gouges and scores the rivet, prong, or post; too big, and it can clip the stone or leave a ring around the rivet. The cup should just about cover whatever you are grinding. 

Cup burs range from 0.9 mm to 10 mm, which is a pretty hefty prong tip. These big boys can be carefully used to refine round bezels or to finish the end of a rod or a really big rivet. 

There are several species of cup bur. Busch makes a squashed-looking cup, de-signed to get into tight places. There are cup burs with side slits to keep them from clogging. I’ve heard that these slit cups give a nice round tip with a great finish.

Cone burs

Straight-sided cones and reamers are good burs for countersinking and gently widening a hole. Generally, they have a sharp point and a more acute taper than a tapered cylinder bur. 

Inverted cone burs

A special-occasion bur, the inverted cone can really save the day. Say, there’s a blob of solder inside a tube or bezel where it meets the backplate, or that too much solder has flooded that inside corner. (I’m imagining this, since it has never happened to me!) You can’t get in there with a file or a disk. You could use a round bur, but that wouldn’t get in the corner, and it would gouge the bottom rather than leave it flat. You could get in with a cylinder bur and use its flat tip and side to grind, but chances are you’ll grind into the side wall, too.

What you need is a bur whose cutter is wider at its tip than at where it meets the shank — a reverse taper. The inverted cone has teeth on its sloped sides and its flat, wider tip. Holding the shaft at 90˚ to the base sheet so that the tip of the bur rests flat, use the bur like a router, working slowly and moving it in small circles. The flat bottom will cut the solder glob, while the edge of the bur nibbles into the corner. Because the taper is inverted, the side of the bur slopes away from the bezel/tube wall. The bottom gets cut (machined), and the corner is left nice and crisp while the wall is left alone — it takes practice. 

Wheel burs

Their squared edge makes them great for grinding flat areas between uprights or carving and refining the bottom of a trough, as in preparing a channel setting.

Miscellaneous burs

There are bur sets designed for wax carving, and there are also strange little three-bladed propeller burs called “wax paddles,” which cut wax quickly and cleanly without clogging. Florentine burs are large cylinders that cut parallel lines: Cut in one direction, then come back and cut across those lines. Oval, knife-edged, and round-edged wheel burs are a few more; there are more still.

When I started out, my first burs came from the family dentist. (It was the least he could do!) They were smaller versions of jewelry burs (they only went up to 2 mm or so) and, while they were used, they were still pretty sharp. I still use them today, and dental lab catalogs are a good place to find strange burs.

Diamond burs

These are the ticket for working with stone, ceramic, glass, or hard metals — anywhere an abrasive type of cutting is preferred. They come in various shapes and quality. I always keep a few diamond ball, bud, and cylinder burs on hand.

SAFETY NOTE: Burs take a while to master. They pull your hand away from you as they spin, and can do damage quickly. Don’t just hold a bur to the work and step on the pedal; success lies largely in skillful manipulation. Wear eye protection, keep your bur lubricated, work gradually (“nibble,” don’t “gobble”), use sane speed, and watch your fingers!

AUTHOR’S NOTE: Thanks to John Frei for his patience and willingness to share his encyclopedic knowledge of tools. (I think he actually really enjoys it.)