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How to use a flex shaft: Part 3 of 7

Here’s the Drill…

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

For the jewelry maker, drilling is a process that enables many other processes. Piercing and riveting begin with drilling a hole, and drill bits can be used to create pattern and texture. When it comes to the flex shaft, drilling may seem to be the simplest of tasks, but there’s more to the story than it first seems.

Types of drill bits

First, let’s define our terms. We often say “drill” to mean the whole assemblage, but to be precise, the drill (i.e., the flex-shaft handpiece) holds and spins the drill bit. The drill bits that we use in the studio are most commonly made from high-speed tool steel, which is harder and lasts longer than other common drill-bit materials, such as tungsten vanadium steel. (Please note that “high speed” refers to the type of steel, not to the intended rpm.) There are also carbide drill bits, which are very hard, very sharp, and very brittle; these are “special occasion” bits for use when you need to cut harder materials. Diamond drill bits, which are steel shanks plated in industrial-diamond grit, will cut anything.

twisted

Twist drill bits

When we think “drill bit,” it’s probably the common twist drill bit that comes to mind. A twist drill bit is a steel shaft with grooves that begin halfway up the shaft and end at the tip. The base, or shank, is the lower, ungrooved portion of the bit. 

As with cutting tools like files or gravers, it helps to think of a drill bit as a chisel. In this context, a file would be a series of small chisels, each lined up after the other. The tip of a drill bit has two opposing chisels with cutting edges that face each other and cut as they spin. A drill bit won’t cut in reverse; like a file, the chisel tips cut when pushed into the metal but not when dragged in the other direction. 

CHART
drill bit types

On a twist drill bit, these chisel tips are called “lips,” and the grooves that spiral around the shaft of the bit are called “flutes.” Flutes don’t really cut; their primary job is to evacuate “swarth,” the cut material (usually chips or windings). If the swarth isn’t removed, it will jam up and bind the bit, causing it to snap.

Most drill bits have a shank that’s the same diameter as the rest of the bit, so an adjustable handpiece (#30 style) is required to accommodate the different sizes. For those who love their quick-release style handpiece, there are choked drill bits. The various shaft sizes of these little beauties all emerge from a 3⁄32-in. (2.38 mm) shank, the most common size used for flex-shaft accessories and for the collets of most quick-release handpieces. The downside to choked bits is that they cost about twice as much as their variable-shank cousins. An economical solution is the adaptor chuck, which holds small bits in an adjustable collet, much like a pin vise, and has a 3⁄32-in. (2.38 mm) shank. 

The tip of a twist drill bit can vary in steepness (the “point angle”) according to the material the bit is designed to cut. An all-purpose point angle is 118°; I use these to drill through metal, plastic, wood, pearl, and even slate. (Bits don’t cut metal well after attacking slate, but they still work on that stone, so I designate them for that task.) Although all-purpose bits will cut plastics, steeper point angles are used to cut Plexiglas and other materials. 

Whether you’re buying plain or choked bits, you’ll usually have to order them in multiples of five, six, or 12, although smaller suppliers may offer them individually. Drill bits are consumable, and I buy the sizes I use most often in bulk.

NOTE: Speaking of size, I select my drill bits by their millimeter measurement. For ordering, though, I remember the drill-bit number and wire gauge equivalents of the bits I use most often:


Diamond drill bits: Twist and core

For drilling stone, glass, ceramics, and hard materials, diamond drill bits are the ticket. Unlike the chisel action of a steel bit, the diamond grit cuts abrasively — it grinds away material rather than chipping it away. The diamond coating is usually plated onto two basic shapes: twist and core. You may also be able to find solid-cylinder diamond bits, but they’re less common.

The diamond twist drill bit is essentially a standard twist drill bit plated with diamond from its flutes to its lips, with the shank left bare. Diamond core drill bits consist of a diamond-coated hollow cylinder.

The cylinder’s rim does all the cutting, and waste material is evacuated through the hollow center and a hole in the side. Diamond drill bits come in a variety of sizes and with choked or straight shanks. 

The one weakness of a diamond drill bit is the bond between diamond and steel. This is where these bits eventually fail due to heat build-up; that’s why they’re meant to be used wet. I periodically dip the end of the bit in water as I drill or hold my work in a shallow, water-filled container.

Safety

A note about safety. Specifically, protecting your eyes: safety goggles, safety glasses, face shield. Pick one. Use it.

Drilling

Using a sharp drill bit is one of life’s pleasures. Using a dull drill bit is like trying to cut a tomato with a butter knife: tedious, dangerous, and in the end, a mess. The key to keeping your bits sharp as long as possible is the holy trinity of speed, pressure, and lubrication. 

Heat, generated by friction, is the main enemy of a sharp drill bit; it tempers and softens the delicate cutting edge. Remember this when you’re tempted to up the rpms; the sound of a flex-shaft motor spinning at top speed is the sound of a dulling and dying drill bit. The foot pedal is not an on/off switch! I start drilling at low rpms and continue at slow speed, gently applying the spinning bit, and even pumping the pedal a little. 

Also, be careful of applying too much pressure; heat builds quickly in a tiny drill bit, and pressure adds to the friction. Too much pressure can flex and break a bit, or deflect it and cause it to wander (like a fine saw blade). 

The third leg in the sharp-bit tripod is lubricant. I’ve used lip balm in a pinch, but common lubricants include bar soap, wax (such as paraffin or beeswax), oil (messy), and a variety of waxy cakes with proprietary names like “Bur-Life,” “Pro-Cut,” and “Stay Sharp.” These come in cylinders that push out like a stick of deodorant or — my favorite — in replaceable cartridges that slot into a simple holder that you screw to your bench. I touch my spinning drill tip to the lube, then drill away. My saw blades, burs, and anything that needs lubrication gets dragged through the little cone-shaped cake. (I even have one screwed to the bench where I draw wire.) It’s also available in liquid drops. Apply lubricant just to the tip of the drill bit.

Avoiding breaks

There are six major reasons a bit breaks:

  • Speed: Drilling too fast
  • Flex: Excessive pressure
  • Deflection: Leaning too far off center
  • Protrusion: Too much bit sticks out of the handpiece
  • Binding: Not clearing swarth
  • Dryness: An unlubricated bit

As a bit dulls, you may be tempted to apply more pressure and speed. Don’t. That will dull the bit even more, leading to more force and more speed, until you finally toss the smoking bit away in frustration. It can also result in a broken bit. 

Bits are also more likely to bend and snap the further they protrude from the handpiece. A longer bit is more likely to bend or wobble — and then break. 

There is almost a sound and feel to a bit just before it breaks. (Odds are, you’ll learn to recognize the signs.) I was taught to pause every now and then, and back the bit out of the hole to clean debris. That’s excellent advice, especially when drilling through thick material. 

The most dangerous time for a small drill bit is when you’ve almost cut through the metal. Overly cautious, you may cut back on the speed and pressure to the point where the thin amount of metal left — little more than foil, really — binds and snaps the bit. Instead, continue to drill confidently through that last smidgen just as you did the rest.

Sometimes, you can get away with using a sharp drill bit without first making a pilot mark in the metal, but generally a punched dimple will keep the bit on target. Most people use a center punch to make a pilot mark, but I prefer to use a scribe or even a sharp engraving tool. Dig the point of the tool firmly into the metal exactly where you want the hole, and wiggle the handle around in an arc. This leaves a neat little mark that the drill bit can find and has the advantage of not collapsing the metal as a hammered center punch might. 

When I’m beginning a hole, I rest my idle drill bit in the pilot mark and then gently step on the pedal and begin drilling. When I’m enlarging an already drilled hole, I usually introduce a slowly spinning bit into the hole. This reduces the chance that the bit will catch.

Despite your careful practice, this will eventually happen: It’s late, you’re tired, and you break a bit off flush in a thick ring. You can’t poke it, drill it, or dig it out. How do you fix it? You can dissolve it in a hot solution of alum. Alum can be found at drugstores (it’s an astringent) or even at the supermarket in the spice aisle (it’s used for pickling). 

Mix the alum powder with hot or boiling water in a Pyrex container until no more will dissolve, and then toss in the afflicted ring. It may take several hours, but the drill bit will go away. Hot pickle also works. I just throw the piece in for an hour or so; the acid eats away the steel bit enough that you can wiggle it free. Sure, you’ll have a little copper-plated area around the hole, but you can buff that off easily. This method works with nonferrous (iron-free) metals like silver, gold, copper, brass, bronze, platinum, palladium, and even aluminum.

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