How to Make a Round Hole Square with a Square File

What You'll Need
Square file

A square file is a very useful shaping tool that can be used for a variety of purposes. Whether it is piece of aluminum sheet or any other type of metal sheet, creating a nearly perfect square hole out of a round hole is not an easy task using a drill. However, the square hole can be polished by using a square file.

Step 1 – Mark the Perimeter of the Square Hole

Determine how large the square hole should be and mark it around the round hole with a pencil and a square or any other tool with a straight edge. Adjust the dimensions of the square as needed and adjust its location if necessary. Double-check the measurements to ensure that the hole to be made will be of the correct dimensions.

Step 2 – Cut the Hole with Chisel and Hammer

If the metal sheet is thin enough, place it on a flat surface and secure it with clamps if necessary. The first method involves using a hammer and a chisel. Place the sharp edge of the chisel directly above a section of the marked square. Tap it lightly with a hammer until the sharp edge pierces through the metal. Move to the succeeding sections and do the same until the entire perimeter of the square is cut. Push the cut metal sheet out of the hole. Notice that the cuts made by the chisel and the hammer do not make a nearly perfect square. This is where the file comes in. Use the file to remove the burrs and smoothen out the interior edges of the hole. Slide the file back and forth on the edges of the hole so until the line is completely made straight and free from any rough edges.

Step 3 – Cut the Hole with the Help of a Drill

If the sheet metal is thicker, use a drill. Place a drill bit in the drill and drill around the entire perimeter of the square. The holes should just lightly touch the perimeter of the square, but should not go beyond the marked lines. Space the drilled holes just slightly a few millimeters apart from each other. Afterwards, use a chisel and a hammer to cut through the gaps in the holes. Ensure that the cuts are made exactly on the marked lines. File the edges of the hole to make it completely square.

Alternatively, you can also just drill a starter hole on one of the corners of the square and let the file do the rest of the work. Insert the file into the drilled hole and move it back and forth as it cuts through the line. When the file meets the end of the line, turn it to the direction of the next line. Work in this manner until the entire perimeter of the square is cut. Check all sides of the hole to make sure they are straight.