A homemade kunai knife looks like a wide dart-shaped arrow with a circle on the end of the handle. The handle is wrapped with grass or leather. This traditional Japanese weapon was used as a gouger. The shape of the knife allowed Ninja warriors to dig into castle walls to gain entrance. It also made a good climbing tool and weapon. Making a homemade kunai knife is extremely time consuming, so allot eight to 12 hours to complete the project.
Draw a 10-inch line on paper. Mark the line at 4 inches and 5 ½ inches.
Place the ruler perpendicular to the line at the 4-inch mark. Draw a line 2 inches long that crosses at that point.
Turn the paper so the 4-inch section of the 10-inch line is pointing straight down. Connect the outer two points of the 2-inch line with the bottom point of the 10-inch line to create a triangular dart shape.
Connect the top points of the 2-inch line with the mark on the centre line at 5 1/2 inches.
Place the point of the compass 1 inch from the top of the 10-inch line. Set the tip of the pencil on the end of the 10-inch line. Draw a 2-inch circle.
Set the compass to 3/4 inch. Place the point of the compass in the same spot. Draw a 1 1/2-inch circle.
Draw a line 1/8-inch from both sides of the centre line to create a 1/4-inch handle between the circular end and the blade.
Cut out the paper knife template.
Brush the surface of the paper kunai knife template with rubber cement. Turn the template over and position it on the 1/8-inch steel. Push it into place and allow to dry for 10 minutes. Draw around the outside edge of the template with soapstone.
Put on the safety glasses/goggles and welding gloves. Secure the knife blank in the bench vice for easy cutting. Cut around the knife shape with a plasma cutter. Cut just outside the shape to prevent breaching the knife shape integrity. Allow the blade to cool.
Remove the cut shape from the bench vice. Grind the edges of the blade to the desired pitch. Grind the square edges from the knife handle and circular end. For example, grind each angled edge at a 30-degree bevel. Flip the knife over and repeat the process on the opposite side of the blade.
File the knife handle, outside of the circular end and the inside of the circular end with diamond files to achieve the desired shape. File the edges with a round diamond file to achieve a rounded edge.
Bevel the outer edge of the blade to achieve the desired sharpness. For example, sharpen the edges of the blade using a 35- to 40-degree bevel.
Wrap the handle with sea grass. Begin under the ring and proceed to the top of the blade. Epoxy the ends of the sea grass to hold it in place.
Rub a layer of oil over the surface of the knife to prevent rusting.
Oil the blade after every use to prevent rusting.