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01 cutting the blank

March 19, 2021

Materials


  • 1lb EPS (Expanded Polystyrene) blank. 96" long x 30" wide x 6" deep.

  • 1/8" panel board for outline template and rocker template

  • Masking tape

Tools


  • Hot Wire Cutter

  • Hand Saw

  • Rasp Plane

  • Sanding Boards, Sanding Square

Steps

  1. The 1lb EPS (Expanded Polystyrene) blank was cut to 96" long x 30" wide x 6" thick at a local EPS warehouse.

  2. Cut 2 rocker templates from 1/8" panel board. Sand the edges smooth. (The bottom shape of my template was flat at the back fin area up to the front foot straps, with a very gradual curve for the nose starting after the front foot straps).

  3. Attach the rocker templates to the sides of the EPS foam with screws or nails.

  4. Use a hot wire to cut the top and bottom shape, slowly pulling the wire across the rocker templates as a guide.

  5. Use a long sanding board to sand smooth any areas as necessary using the rocker templates as a guide.

  6. Use a marker pen to draw a centerline down the middle of the top and bottom of the board.

  7. Cut out a board outline template from 1/8" panel board. Sand the edges smooth. Just make a half board template that you can flip over to use for the other side. This will insure that each side is identical.

  8. Use the board outline template to draw an outline on the top and bottom of board.

  9. Remove the rocker templates from the sides of the board.

  10. Cut out the board shape about 1cm on the outside of the line using a hand saw (placing a mirror on the floor can help you see the underside of the board as you cut it).

  11. Shape the board edge square to within about 2-3mm of the the outline first using a rasp plane, then a square sanding board. (The edge does not need to be finished until you have added the sandwich core material to the hull).

Notes


  • EPS density is rated in lbs per cubic foot, and 1lb is what most production windsurfing boards are made with (16kg/m3). EPS comes in other densities such as 1.5lb or 2lb per cubic yard, which are often used for surf board blanks.

  • I created the rocker templates and board outline design in Adobe Illustrator at 1:1 scale. For the rocker template, I took measurements in Illustrator at various intervals along the rocker and transferred those measurements to the panel board. For the board outline, I took measurements from the centerline to the edge of the board at 10cm intervals. I used these measurements to then create the board outline template. Masking tape was used to create a smooth line between the points I marked on the templates (see the outline template above with tape still around the edge).

  • I made a hot wire cutter using a power supply/battery charger with 26 gauge nichrome wire. I think 24 gauge wire would have been better at maintaining the correct temperature. When using a hot wire the wire should be hot enough so that it actually melts the EPS just before touching it. You should not have to pull it through the EPS, and it should not leave lines in the EPS. The wire will stretch as it gets hot, so you will need a tension system - a short bungee cord worked very well! The wire can be cleaned between uses with steel wool or fine sandpaper.

  • The sanding square was made using a metal bracket and 4" x 1/2" steps of wood, with 60 grit sandpaper glued to one surface with contact cement.

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