Updated better method here.
Cutting a square hole in sheet metal.
Jigsaw and a file.
Tap your hammer to leave an indentation on the sheet metal.
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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.
Ensure you fix the metal sheet down when you drill do not hold in you hand.
How to use chisels instead of files to cut a share hole for carriage bolts.
Go slow and drill a smaller hole first ti guide the bigger rill bit.
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Drill a hole large enough for a jigsaw blade in the part you re cutting out then cut it out with the jigsaw you ll have to curve into the straight lines of your square hole and do a little whittling but it works.
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Depending on the tools you have you ll now need to punch or drill a hole where the indentation has been made to produce an accurate hole in your sheet metal.
In this case w.
Https youtu be m3ul s9 ma0 make your own homemade broaching tool for drilling perfectly square holes in steel.