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Heat your oven to about 400 °F (204 °C). Put a pan containing the plastic in the oven and heat it until it is completely melted.  Parental supervision is suggested Make sure the plastic is in a pan large enough to support the melted goop. Allow the plastic to cool enough that it is still pliable. Do not let it harden. Carefully shape the plastic into sunglasses with eye-holes. This allows you to fit the accessory to your head quite well. Cut off the earpieces in a shape like this. _/\_  Then, drill small holes in the ends of the shapes /\ and \/. Finally, screw on the earpieces to the main plastic part of the sunglasses. Cut out the acetate sheets to the size of each lens with a little extra around the edges. Then glue the acetate sheets to the plastic mold. If the plastic is still pliable, feel free to insert the acetate inside the plastic.
Melt some plastic. Let the plastic cool. Mold  your sunglasses. Make the earpieces. Make the lenses.