What Are Step Drill Bits Used For?

We’re sure you have at least one power drill in your woodworking shop. They are pretty essential tools to have, whether corded or cordless or even a drill press.

Along with the drills, you likely have a variety of bits for them, and the types of drill bits you have will depend on the type of work you do or the projects you work on. Power drills usually come with a few standard drill bits, but the type of drill bit you use is chosen based on the diameter of holes your project requires.

The drill bits will come in different diameters and lengths, and it might be a pilot hole you need, a starter hole, or a specialty hole – for instance, a pocket hole joint. We’ve written of pocket hole joinery in the past, most recently here.

But then there are even more specialty holes beyond the pocket hole and special drill bits beyond the standard drill bits that came with your power drill. The step drill bit is one of them.

What Are Step Drill Bits?

Step drill bits, also referred to as unibits, are a conical-shaped drill bit that, by virtue of their shape, allows you to drill holes of varying sizes. The deeper you drill into the material you’re working with, the larger the hole will become.

This obviates the need to change drill bits while drilling holes, for instance. It also makes it easier to drill larger holes a little bit (no pun intended) at a time as you push the drill bit further into the materials.

These specialty drill bits are capable of drilling into metal, for instance, up to ¼ “ thick, and are common on construction sites. Their use, though, is not limited to sheet metal; step drill bits are also used for drilling holes in plywood, drywall, laminate, plexiglass, and particle board.

You will often see an electrician use a step drill bit to drill holes in plastic switch and outlet boxes when roughing a new construction for wires to fit through or in studs as a new house is being rough-wired before sheetrock or drywall is hung. Since many of us woodworkers are also home DIYers, it’s handy to have step drill bits for our power drills when we need larger holes and not just holes in sheet metal.

Step Drill Bits In Use

If you have ever tried to drill through a thin piece of sheet metal with a traditional fluted drill bit, you’ve likely encountered problems.  A traditional twist drill bit, like those standard drill bits that come with a power drill, will often catch a burr and be pulled right through. When clean holes are needed, this is a bad result.

Very small holes are okay with twist drill bits, but once the hole size needed is much larger than the material being drilled, a step drill bit is a much better choice. Their straight flute will help prevent thin, flexible materials from being twisted out of shape as the drill passes through them.

Step Bit Sizes

Step drill bits will usually have their diameters etched into them for easy reference when looking through your collection. The smaller diameter step drill bits usually have a sharp point at the tip to make them self-starters that don’t need a pilot hole drilled first.

Larger step drill bits are blunter and cone-shaped and will always need a pilot hole drilled that is the same size as the drill bit’s smallest step. If it is sheet metal you are drilling, a punch will be used to mark the center of the hole to be drilled, and then the step drill bit will take it from there.

When drilling sheet metal, there will sometimes be burrs that will need to be cleaned out of the hole before you proceed. Step drill bits are also well-suited to clean holes to finish the drilling.

They are also a great tool for enlarging an existing hole. Simply go deeper with the step drill bit, or change to a larger one to enlarge the hole already there to the size you need.

Additionally, if a chamfered edge is something you want, you can accomplish this simply by tapping the hole you’ve drilled with the next level’s bevel on the step drill bit. It might help if you are using a wide head screw that you want to lay flush on the surface of the material you’ve drilled.

Step Drill Bit Materials

There is a wide variety of materials used to manufacture step drill bits, and each has its own strength of use.

• High-speed steel. These step drill bits are good for drilling into soft materials, including wood, fiberglass, and plastic. They would suit that electrician who needs to drill holes in the plastic wall outlet or plug boxes, as well as drill through studs when rough-wiring a new construction. They are also the least expensive step drill bits.
• Black oxide-coated high-speed steel. The added finish coating will retard corrosion. This enhances durability and makes them a better choice for drilling into harder metals.
• Cobalt bits. More brittle than HSS bits but much quicker to cool down after use when drilling metals. Cooling down faster helps them keep their stiffness when temperatures rise while drilling.
• Titanium-coated and carbide tipped. The former is much more expensive, but they hold their sharp better and longer. This makes them a good investment if you will be using them often. The latter will hold their sharp even longer and are well suited for drilling into masonry and tile work.

Safety Measures When Using a Step Drill Bit

We subscribe to the safety first rule and have repeated this often on these pages. When using a step drill bit:

Always wear safety goggles. Especially if you are drilling into metal. Burrs and bits will often fly, whether using a hand-held power drill or using a drill press. Metal shavings are much more dangerous than bits of wood and can damage your eyes and face easily. A face mask wouldn’t hurt, either.

Find the center of the hole. Measure well and mark better. Punching an indentation in a metal sheet or a plastic sheet will get you off to a better and much more accurate start so that you only have to drill once. The dent marks the spot and makes the drilling more exact.

Using a lubricant. If you are drilling into metal rather than wood or plastic, a lubricant will help make the drilling easier. Use a self-starting step drill bit to begin the hole, and remember that the more pressure you apply, the greater heat will be generated – you want to avoid this, if possible, as it will dull the bit. At the first sign of smoke, stop drilling and let everything cool down.

A step up. If you’ve taken the smaller step drill bit as far as you can and the hole needs to be larger, add more lubricant when you swap it out for a larger bit, and follow the same rules about smoke.

Clean up after yourself. When you are finished with drilling, be sure to clean up the hole of any burrs that developed and clean off the drill(s) used. Wipe any metal shavings off the bit before returning it to the toolbox.

Strengths and Weaknesses of Step Drill Bits

On the plus side, we have:

• Single bit, varying diameter holes. The depth of the drill with a single bit will determine the diameter of the hole without having to change bits.
• Round matters. A smooth and round hole is a strength of using step drill bits.
• So does size. Step drill bits are smaller than standard twist drill bits and can fit into tighter spots.

And on the downside, we have:

• Durability. Step drill bits can wear down fast, even with proper use.
• Difficulty sharpening them. Their unique shape makes keeping them sharp a real chore.
• Price. A good set of step drill bits can be very expensive.

Step Drill Bit Prices

While you can find a set of 4 different-sized step drill bits for under $20 (we found some at the large online retail site in the upper teens), as you move up in the materials and coatings available in the marketplace, the cost goes up steeply.

The less well-known brands will be your best bet for a small set of HSS drill bits at that lower price point. But, for the coated and fancy-tipped drill bits and the more well-known brand-name manufacturers, you will pay a lot more.

A DEWALT step drill bit, just one, might run you more than $40; a single step drill bit from Lenox might be closer to $30, and a Milwaukee brand single bit will be just below that price point.

An Introduction to Step Drill Bits

If you’ve never used a step drill bit, we found a video that will introduce you to them. You’ll be able to see the gauge markings on the drill bits to identify the diameter of each step, and you will see how the videographer flipped the metal workpiece to use the step drill bit to clean out the other side of the hole he drilled. You’ll also hear him discuss safety precautions when using them to drill metals.

As we have said, step drill bits are not just for drilling metal; plastics, plexiglass, laminates, wood, plywood, drywall, and more are materials that a step drill bit might be a good choice for when a hole is needed.

An HSS step drill bit set won’t break the shop’s budget, and a set of 4 might come in handy someday. While not essential, not all woodworking shop projects are all about only wood. Sometimes in the DIY home renovation work we all do, a step drill bit might very well come in handy.

At the least, consider it. You already have a power drill in your tool inventory, if not a drill press. Better to have and not always need than to need sometimes and not have.

Last update on 2024-09-09 / Affiliate links / Images from Amazon Product Advertising API