How to Cut Thin Sheet Metal and Keep It Flat

About: Left school at 14 and took on a 6-year apprenticeship for radio and electronics, It was vacuum tubes then), the last 2 actually working for the Technical college I was studying at. Moved on the aircraft ele...

Intro: How to Cut Thin Sheet Metal and Keep It Flat

If you use metal shears to cut thin sheet metal such as duct metal, it curls and can be difficult to flaten properly. These photo-steps show that it can be done using a utility knife. The illustrations are for a small bracket, but I have cut 3 foot long pieces using this method. You just need to be careful and take your time making several scoring lines and not pressing too hard. Snap off a piece of blade as necessary and don't use the thinest blades or the extra heavy duty types.

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    5 Discussions


    1 year ago

    This is possibly the most useful tutorial I've seen anywhere. For the cut-out, it occurs to me that you could drill a small hole at each corner prior to cutting. Not only would this make it easier not to overshoot with the knife, , but would also help prevent cracks from propagating from the corner


    2 years ago

    I'm surprised that such simple tools can be used to cut sheet metal! I wouldn't have thought that a normal utility knife would be able to do the job. Granted, I'm sure that it wouldn't work as well with thicker metal, but it's still impressive that tools that I have at home would be able to cut the sheet so well. Thanks for the instructions; I feel like even I could cut some metal sheets, though only if they were pretty small.


    3 years ago on Introduction

    Thank you for such a detailed tutorial. I need to install some metal weatherstripping and wasn't sure how to trim it for the bolt and latch. Scoring it first with a utility knife seems like it will allow me to make precise cuts without deforming it.


    4 years ago on Introduction

    very interesting. didn't even consider to use those cutters. Can you tell me which metals (and thickness) you can cut that way?

    1 reply

    Reply 4 years ago on Introduction

    The brackets in this instructable were 0.01" (10 thou) thick, but I have 'cut' metal up to 0.025" (25 thou) this way. The thicker metal requires more scoring before you attempt to bend the metal back-and-forth to brake it.
    On particularly thick metal, I have turned the piece over to score the back-side along the same line as the front, but you have to be very careful to score on exactly the same line as the front, otherwise you will get very sharp needle-like edges or at worst a double brake along the score line. Place the metal on a hard surface to score it and on long pieces, do the bending with the score place along a sharp edge of a bench and, if necessary, clamp the 'fixed' piece with a long piece of flat wood to prevent buckling the metal while bending it back-and-forth.
    I hope this reads sensibly.