Go slow and drill a smaller hole first ti guide the bigger rill bit.
Making a sqaure hole sheet metal.
Next use a compass to outline the edge of the hole.
Blacksmithing for beginners cutting a square hole in sheet metal.
Use your center punch to strike at the center of the hole.
How to use chisels instead of files to cut a share hole for carriage bolts.
Drill a hole in the metal close to but smaller than the finished hole size.
Making a square hole in a plough blade.
At first locate the center of the whole.
How to make a square hole without using special tools.
Insert the broach and ensure it lines up at 90 degrees from the work peice or the hole will be crooked.
If the hole is a lot bigger then your biggest drill bit then drilling holes round the edge of the square and then connecting them with a saw is the best way for you.
This will create dimples in the sheet.
Ensure you fix the metal sheet down when you drill do not hold in you hand.