What is Drilling?- Definition, Process, and Tips

What is a Drilling?

Drilling is a method used to create holes in solid materials, typically by spinning a drill bit. This bit most often a rotary cutting tool with multiple cutting points is pressed firmly against the surface of the material and rotated at high speeds, sometimes reaching thousands of revolutions per minute. As it spins, the bit’s cutting edges gradually shave away material, producing chips or swarf and forming a round hole.

When it comes to drilling into rock, the approach can differ quite a bit. Instead of relying solely on a steady circular cutting motion, rock drilling usually combines rotation with a rapid hammering action. The drill bit is repeatedly struck, either from inside or outside the hole, which helps break up tough material. Drills designed for horizontal rock drilling are referred to as drifter drills.

Although most drilled holes are circular, there are some unusual situations where specially shaped bits are used to create holes with a non-circular cross-section making it possible, for example, to drill a square hole.

Related Posts: What is a Drilling Machine?

Drilling Process

When it comes to drilled holes, there are a few things you’ll typically notice right away. On the entry side, the hole is usually defined by a sharp edge, while the exit side often shows burrs a common byproduct of the drilling process. Inside the hole, you can spot the helical feed marks left behind by the drill bit as it worked its way through the material.

Drilling isn’t just about making holes; it can also subtly change the mechanical properties of the workpiece. For example, the act of drilling tends to create low residual stresses around the opening, along with a thin, highly stressed, and sometimes disturbed layer on the fresh surface inside the hole.

Unfortunately, this stressed layer makes the material a bit more vulnerable it’s more prone to corrosion and cracking over time. That’s why, in many cases, you’ll see a finishing operation done afterward to smooth things out and reduce those unwanted effects.

With fluted drill bits, chip removal is handled by the flutes themselves. The nature of the chips whether they come out as long spirals or break up into small flakes can tell you a lot about the material you’re working with and how easily it can be machined. Generally speaking, long chips are a sign that the material is pretty machinable.

Ideally, drilled holes should be placed perpendicular to the workpiece surface. This simple step goes a long way toward preventing the drill bit from “walking” off the intended line a common issue that can lead to misplaced holes. The risk of walking increases as the drill’s length-to-diameter ratio gets larger. There are several ways to keep the bit on track, such as:

• Marking the center before drilling, which can be done by casting, molding, or forging a mark right into the material, or by using a center punch, spot drilling, or even spot facing to create a smooth, accurate surface on a rough casting.
• Using a drill jig with bushings to physically guide the drill into position.

As for the surface finish inside the hole, it can vary quite a bit ranging from about 32 to 500 microinches. If you’re aiming for a finer finish, a finishing cut can get you closer to the lower end of that range, while rough drilling will leave things rougher, nearer the higher end.

Cutting fluids play a crucial role in the drilling process. They help cool the bit, extend its lifespan, improve the surface finish, and make it easier to clear out chips. These fluids are typically applied either by flooding the work area or using a spray mist, depending on what the job calls for.

Finally, picking the right drill for the job matters more than you might think. There are many types of drills out there, each tailored to specific tasks. For instance, a sub-land drill can handle multiple diameters in one go, a spade drill is designed for making larger holes, and an indexable drill excels at managing chips.

12 Tips for Drilling Holes in Metal

At some point, most DIY enthusiasts will find themselves needing to drill through metal, whether it’s for a home project, a repair, or something more creative. There’s actually a surprising variety in both the types of metal you might encounter and the ways you can approach drilling into them.

While drilling into metal isn’t necessarily more complicated than working with wood, there are a few key differences to keep in mind. For starters, you’ll need to gather a couple of extra supplies and adjust your technique a bit.

Just about any portable drill will get the job done though if you happen to have a drill press, that’s a bonus. As for the drill bits, you’ll generally use the same high-speed steel bits that work for wood, which makes things easier.

The biggest things to remember when drilling through metal are safety and patience. It’s important to use the proper safety gear and take your time, especially because drilling too quickly can cause the bit to overheat or even damage the material.

Most of the techniques you’d use will work across a range of metals whether you’re working with thin sheet metal, aluminum, or something tougher like a thick steel plate.

Here are 12 tips to make the task fast, easy and safe.

1. Drill Bits Required for Metal Drilling

When it comes to drilling holes in metal, most general-purpose twist bits are quite effective. Interestingly, the majority of drill bits designed for metal are also capable of handling materials like wood and plastic, making them versatile tools in any workshop. The more affordable twist bits are typically made from high-speed steel (HSS), which tends to be sufficient for standard metal drilling projects.

However, if you find yourself frequently drilling holes, or if you’re working with particularly tough and abrasive metals such as stainless steel or cast iron, it’s worth considering an upgrade. Investing in black oxide or cobalt steel bits may cost a little extra, but these options maintain their sharpness longer and can handle more demanding jobs without dulling as quickly.

Additionally, some drill bits are coated with titanium nitride (often abbreviated as TIN). Manufacturers suggest that this coating enhances resistance to heat and friction, which means the bits can have a lifespan up to six times greater than standard high-speed steel versions.

2. Protect Your Eyes

Even a single small metal shard can lead to a significant eye injury, making it essential to use appropriate eye protection whenever drilling into metal. For optimal safety, it’s advisable to wear safety glasses that offer side protection by wrapping around the contours of your face.

3. Make a Center Punch

When you begin drilling, it’s common for the drill bit to slip off your intended spot, which can throw off your accuracy. A practical way to avoid this is to start by carefully measuring and marking the exact location for your hole.

After that, take a center punch and give it a firm tap with a hammer to make a small indentation. This little dimple acts almost like a guide, allowing the tip of your drill bit to settle in and stay put as you start drilling.

4. Lubricated Bits Last Longer

When working with steel that’s at least 1/8 inch thick, it’s a good idea to use a cutting fluid or even something as common as 3-IN-ONE oil. Adding a bit of lubrication helps keep friction and heat under control while you drill.

Not only does this make the job smoother, but it also helps your drill bits last much longer. On the other hand, if you’re dealing with metals like aluminum, brass, or cast iron which tend to be a bit more forgiving you can usually get away without any lubricant at all.

5. Clamps Prevent Stitches

It’s important never to hold a piece of metal with one hand while drilling through it with the other. When drilling metal, the bit can easily catch, which may cause the workpiece to spin out of control and potentially injure you.

Sharp metal edges can cut deeply and quickly sometimes even down to the bone. To keep yourself safe, always secure your workpiece with at least two clamps before you begin drilling. This way, your hands are clear of harm’s way and your project stays firmly in place.

6. Start with a Small Hole

If you need to create a large hole in metal, it’s actually best to begin with a smaller drill bit. Although twist bits can be found in sizes up to an inch in diameter, starting with a 1/4-inch bit gives you more control and helps prevent mistakes or damage to your.

7. Deburr the Hole

When working with metal and drilling holes, it’s common for sharp edges or small metal burrs to remain around the opening. While there are specialized deburring tools available for this task, it is not always necessary to purchase them right away.

An effective and straightforward alternative involves using a twist drill bit that is slightly larger than the hole you’ve made.

By placing this bit at the opening and rotating it gently by hand, you can efficiently smooth the edges and remove any leftover burrs. This simple technique can help ensure a cleaner, safer finish without the need for extra equipment.

8. Hole Saws Cut Bigger Holes

When dealing with larger holes, a hole saw is an efficient tool that produces clean results in a short amount of time. Similar to twist drill bits, hole saws can be attached directly to your drill and are capable of cutting through thin sheet metals, such as aluminum and steel.

To ensure accuracy and protect your work surface, it’s helpful to place a piece of scrap plywood underneath. This serves as a backing for the hole saw’s pilot bit and adds an extra layer of protection for the material beneath.

9. Drill at a Slow Speed

The relationship between drill bit speed and heat generation is straightforward: as the bit spins faster, it tends to heat up more quickly. This increased heat can cause drill bits to become dull much faster than usual.

To preserve the longevity and effectiveness of drill bits especially those designed for metal it is generally advisable to use the slowest practical speed during drilling.

This becomes even more important when working with harder metals, such as steel, or when using larger diameter bits. For instance, small twist drill bits, ranging from 1/16 inch to 3/16 inch, are typically suitable for drilling through most metals at speeds up to 3,000 rpm.

However, as the diameter of the bit increases, slower speeds become necessary. For larger twist bits say, between 11/16 inch and 1 inch in size a range of 350 to 1,000 rpm is more appropriate. By paying attention to speed and bit size, you can minimize heat buildup and extend the life of your tools.

10. Make a Sandwich

When you need to drill neat, accurate holes in thin sheet metal, try this straightforward technique: make a “sandwich” using two pieces of wood. Place your sheet metal between the wooden layers and secure the whole stack firmly with clamps on your workbench or table.

The wood on either side helps hold the metal flat and steady, so when you start drilling, the bit won’t skid around or deform the metal. This simple trick can make a big difference in both the quality and safety of your work.

11. Try a Step Bit

Step drill bits are particularly useful for creating clean, precise holes in sheet metal and other thin materials. If you’ve ever tried drilling into a steel junction box, an electrical service panel, or even a stainless-steel sink, you’ll know how challenging it can be to get a tidy result with standard drill bits. That’s where step bits come in handy they’re designed to make this kind of work much easier.

One of the great advantages of using a step drill bit for metal is the versatility it offers. With a single bit, you can make holes of various diameters, rather than switching out multiple bits for different sizes. Some step drill bits are even tough enough to handle metal up to 3/8 inch thick, which is pretty impressive for something that looks so simple.

It’s worth mentioning, though, that this convenience comes at a cost. Step drill bits tend to be pricier than your regular drill bits. But if you’re after clean, well-sized holes without the hassle, they’re often well worth the investment.

12. Step Up to a Drill Press

Drilling holes in metal with a handheld drill is certainly doable, but anyone aiming for more precise and reliable results will likely find a drill press to be a better option.

These machines are actually designed with metalworking in mind, providing a stable platform and a mechanism that guides the drill bit straight down into the material. This setup makes it much easier to create clean, accurate holes without the bit wandering.

Another advantage of using a drill press is the robust, cast-iron worktable that often comes with it. You can easily adjust the height and angle to suit your project, and the table offers plenty of ways to secure your workpiece for added stability.

Adjusting the drilling speed is pretty straightforward, too—you just pop open the top cover and move the drive belt between pulleys to match the material you’re working with.

When it comes to cost, floor-standing drill presses can be quite an investment, but there are solid benchtop models available that don’t break the bank. For around $100, you can get a reliable unit that covers most metalworking needs in a home shop or even a small professional setting.

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