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Among its many uses, sheet metal is often used to route wires or for mounting purposes, requiring you to cut holes. In this article, learn four methods for cutting perfect, smooth, round holes in sheet metal. We’ll also give you tips and tricks about working with different metals, and explain when to use which method.
What Is Sheet Metal?
Sheet metal is a catchall term, referring to metal that has been machined into thin, flat pieces. It can range from very thin (such as foils) to quite thick (plate steel).
Sheet metal is useful in a variety of applications, from decorative to utilitarian, and even structural uses. It can be bent, curled, stamped, or hydroformed, among dozens of other possibilities.
There are several different methods for cutting round holes in sheet metal. Keep reading to learn about four of them.
Tips for Cutting Holes in Sheet Metal
While there are many different ways to achieve the same goal, there are some basic things to know about making holes in sheet metal.
- Clamps are not optional. Most of the methods we’ll discuss use rotational force to drill through the sheet metal. Should the metal sheet become caught on the drill and begin to spin, it essentially becomes a large blade or propeller. The risk of injury is high, and the consequences can be devastating. Never, ever cut or drill sheet metal without clamping it first.
- Mask or sacrifice. As the drill pushes its way through sheet metal, the friction and heat can cause changes in the metal. This might result in discoloration, deformation, or a messy, jagged hole.
Clamping the sheet metal to a sacrificial wooden board is one way to prevent tear-out on the back side of the sheet. Another way is to apply tape over the area where you will be drilling. For delicate sheet metals, or when drilling holes in pre-finished metals, go ahead and tape the front of the sheet as well for extra protection.
- Find center. If you like, you can use a compass or a circle template to draw an outline of your circle in permanent ink. You can also use a scribe to mark the circle’s edges. What’s essential, however, is marking the center point of your circle.
A manual center punch struck with a ball peen hammer will do the job, creating a dimple you’ll be able to find with your drill bit when it’s time to cut the hole. Automatic or spring-loaded punches can also achieve this step quickly and easily.
- De-burr. You’ll have more or less burring depending on which method you use. If you’re using grommets or rubber trim, you might not need to deburr. A handheld deburring tool makes quick work of excess and jagged material. You can also spin a twist drill bit in the hole by hand for removal of minor burrs.
How to Cut Round Holes in Sheet Metal
You can cut round holes in sheet metal using any one of the methods below; twist drill bits, step drill bits, hole saws, hand punches, or a knockout punch. Whatever method you use, wear gloves and eye protection to reduce the risk of sheet metal injury.
1. Use Twist Drill Bits
The most common kind of drill bit, twist bits have spiral-shaped grooves called flutes cut into their surface. These grooves cut through sheet metal to make a hole.
- Drill a pilot hole. The smaller diameter bit you choose, the easier this step will be. Position your pilot bit in the dimple at the center point of your circle. Drill a very small, very straight hole directly through the sheet metal.
- Widen the hole. Remove your pilot bit and choose a new bit that is slightly larger. Center the bit in the pilot hole. Drill straight through the sheet metal, widening the hole.
- Repeat. Keep repeating this process with subsequently larger twist drill bits until you reach your desired diameter of hole.
2. Use a Step Drill Bit
A step drill bit features a single flute or groove. The base of the bit is wider than the tip. Created especially for thin materials, step drill bits eliminate the need to drill multiple holes and switch out bits. They also produce less burring than twist bits.
- Attach the step drill bit. Choose a step drill bit with a base the size of your desired hole, and insert the mandrel or arbor into your drill chuck. A self-starting step drill bit does not require a pilot hole. You can use a self-starting step drill bit to drill the pilot hole for a hole-enlarging step drill bit.
- Drill. Position the bit over the dimple that marks your hole’s center point. Use steady pressure and a slow speed to drill all the way through the sheet metal.
3. Use a Hole Saw
For hole diameters between three-fourths of an inch all the way up to six inches, a hole saw is a great choice. The serrated blade edge of these cylindrical shaped bits saws through the edges of the circle.
- Use a backer board. Hole saws tend to create a lot of tear-out and burring. You’ll want to spend some time cleaning up the hole at the end, but to minimize the work you have to do, use a backer board. Tightly clamping the sheet metal to a sacrificial board has the added benefit of helping the bit stay aligned as it completes the cut.
- Assemble your bit (if necessary). Insert the pilot bit into the arbor or mandrel, and attach the bit to your drill chuck. (Some models come with a permanently installed pilot bit, so this step may not be needed)
- Adjust your RPM. The type of material you are cutting and the diameter of your desired hole are two factors to consider before you start drilling. Check the manufacturer’s details for your hole saw, and set the rpm of your drill to match the speed listed on the included chart.
- Lubricate (if necessary). Lubrication during cutting has two purposes: to make the cut easier and cleaner, and to extend the life of your saw. You can use cutting fluid whenever you like, but it’s essential when cutting through harder sheet metal, such as steel.
- Position yourself. Should the hole saw bit catch in the metal, it can wrench the drill out of your hands and spin for a few moments before slowing to a stop. Arrange your body in such a way that this wouldn’t cause injury.
- Drill. Use consistent pressure and allow the saw to work its way through the sheet metal and all the way into the backing board. Back the hole saw out of the hole and use a screw or screwdriver to knock out the waste from inside the bit.
4. Use a Hand Punch
Hand punches quickly and easily produce small round holes in sheet metal, with minimal burring or jagged edges.
- Install your chosen punch and die set. The punch you choose must be the same size as your die. Install them into the jaws of the hand punch.
- Align with the center point. Position the center of the punch over the exact middle of your desired hole.
- Squeeze. Squeeze the handles of the hand punch together, forcing the punch through the sheet metal and into the die. The waste material should drop out, allowing you to remove the tool.
5. Use a Knockout Punch
Electricians tend to carry knockout punches of all sizes, as they quickly and easily make holes of the diameter needed for conduits. For laypeople, this isn’t economical, but smaller sized knockout punches can be found affordably.
- Drill a pilot hole. Use a twist drill bit or a step drill bit to make a small pilot hole in the sheet metal. The draw stud will be inserted into this hole, so size accordingly.
- Prepare to punch. Placing the die over the draw stud, insert the stud into your pilot hole. Thread the punch onto the draw stud by hand, stopping when it touches the sheet metal.
- Punch. Turn the draw stud using a socket or wrench, gradually pulling the punch through the metal. When no sheet metal remains between the punch and the die, your hole is complete. Unthread the punch.
- Deburr the hole. Use a method of your choice to remove any burrs or jagged edges from the exterior of your new round hole.
Sheet metal is a thin and flexible material with many uses. Making holes in sheet metal is a quick and easy process with the right tools. To make a single small hole, use a hand punch or a twist drill bit. To make a large hole, use a hole saw or a knockout punch. Use a step drill bit to easily and gradually increase the size of the hole without switching bits.