How to cut foam core with 45 degree sides

Written by dan ketchum
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How to cut foam core with 45 degree sides
Sharp craft knives can be used to make smooth cuts in foam core. (careful! image by Josef F Stuefer from

Foam core --- a craft material made from thin layers of plastic foam and laminated paper --- serves as a handy mounting board for posters, graphic designs, photos and prints. Artists and hobbyists often cut foam core into square or rectangular shapes which feature 45-degree angles on four sides. Though rigid, foam core can be cut rather easily. You only need a handful of supplies and a few minutes to make 45-degree cuts in foam core.

Skill level:
Moderately Easy

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Things you need

  • Pencil
  • Angle ruler or T square
  • Craft knife

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  1. 1

    Position the foam core flat on a stable and solid flat surface. Place a mat under the foam core to avoid damaging the surface below. Make sure that the glossy, paper side of the foam core board is facing up.

  2. 2

    Sketch out the shape of the cut you'd like to make -- including any sides with 45-degree angles -- in the foam core, lightly marking the board with a pencil.

  3. 3

    Place an angle ruler or T square atop the foam board. If using an angle ruler, make a 45-degree angle and lock the ruler. Position the 45-degree angled joint of the ruler or T square over the sketch of the 45-degree side angle.

  4. 4

    Press the angle or T square firmly and cut along one edge with a craft knife. For the first cut, penetrate only the top paper layer of the foam core. Cut against the ruler rather than trying to follow along its side.

  5. 5

    Cut into the initial groove, keeping the ruler or T square in place as guide. Penetrate the foam layer of the board this time.

  6. 6

    Cut into the line once again to slice through the bottom piece of paper.

  7. 7

    Repeat the cutting process along the ruler or T square's other edge to complete your 45-degree angle cut.

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