Creating a hole in a piece of sheet metal seems straightforward at first; just grab your drill and the correct-sized bit, and off you go! But things aren’t quite as simple when you need to cut a square hole. Drills, obviously, use round bits; so how does one create a square hole? The problem gets even trickier when the hole needs to be clean and square. Freehanding a few cuts with a metal hacksaw won’t suffice for precision work.
Here are three possible methods for creating a square hole. Which one you use will depend on the size of metal you need to cut, the level of precision necessary, and the tools you have available. We’ve also included a couple of alternate methods at the end!
Method #1: Drill Bit and File
This is one of the simplest methods out there. Start by using a small drill bit to create accurate starting points. Next, use the largest drill bit you can to create a circle whose diameter matches the width of the square hole you need. With the size established, take your file and widen the circle out to create a perfect square.
This method works best with smaller holes. Filing away the edges can be challenging work, but it allows you to be as accurate as you need. Files can also be used to smooth out the burs on the hole.
Method #2: Dremel Tool
This method works for any saw, really. But for small holes in thin-gauge metal, a Dremel tool works fantastic. The tool is small enough to be controlled easily by hand and make accurate cuts. The same technique can be used with a larger circular saw, but you’ll probably get less accurate cuts and a coarser-looking hole.
Related to this method, you could use a reciprocating saw to achieve the same effect, particularly with large holes. Cutting large square holes in sheet metal with a hand-held saw is tricky, however, and you’re likely to need some filing and smoothing after you’re done. If you just need a rough hold quickly, it’s a good method to consider.
Method #3: Square Punch
A punch is a basic bit of any craftsman’s tools; a set of short metal rods sized to match standard drill bit measurements. Unlike a drill, punches are used to push through a piece of metal or to enlarge an existing hole to a standard size – to “punch” through.
Square punches or square-head punches are the same ideas, except the point of the punch is squared off to produce a square rather than a circular hole. Square-head punches can be purchased in standard sets. For a metalworker who is frequently needed to produce uniformly-sized square holes in sheet metal, a set of square punches can be an ideal solution. They are generally for small holes only.
Some other alternates:
Using a mill to create a square hole will likely require some finishing work with a file. You can use a cutting head smaller than the dimensions of the finished hole, then create a square pattern. The finished product will be a square hole.
A nibbler is a pair of shears or scissors, but specially designed for sectioning metal. There’s a bit of a size limit here; nibblers generally aren’t suitable for thicker pieces of metal or particularly hard alloys. But for working with aluminum or similar softer metals, a nibbler provides a low-tech way to cut whatever pattern you need.
Drill and saw
A variation on the Dremel or saw method above. For larger holes in sheet metal where a clean cut is necessary but a hand-held saw is the only option, first use a drill to create numerous holes all along the perimeter of the square. This will help to give an even outline of the hole and provide a starting point for your saw. Then simply connect the dots of the drilled holes with your saw.
These are some basic methods to create a square hole in metal. Be creative and choose the method that matches the tools you have and the characteristics of the metal you’re cutting. Remember to use proper safety equipment such as eye protection to shield yourself from flying debris.