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Plug and Yoke


  1. Sometimes it is necessary to make complex curves and shapes in plastic.

  2. To create these shapes you may consider using the plug and yoke press forming techniques.

  3. Trays, dishes, magazine racks, and vases are just some of the products that may be made using the plug and yoke technique.

  4. Thin sheet acrylic is shaped using a two-part former. One of these is the male part of the former and the other the female part of the former.

  5. The thickness of the material has to be carefully considered. The gap between the male and female part of the former has to be about one and a half times the thickness of the plastic sheet.

  6. The male part of the former called the plug needs to have a slight taper with rounded corners and edges. This allows the plug to be easily removed.

  1. The acrylic or Perspex is heated in the oven until it is soft and malleable.

  2. The female part of the former, which is called the yoke, is pushed onto the male plug.

  3. It is essential that the two parts of the former align properly. In order to ensure this two dowel rods called locating pins. These are fixed into holes drilled into the corners of the plug. The pins also fit into holes drilled into the yoke.

  4. The draw is the amount of plastic that is pulled down to form the sides of the plastic tray or plate.

  5. The size of the plastic sheet used needs to allow for the depth of the draw.

The stages of press forming and using a Plug and Yoke.

  1. When the plastic sheet has been heated so that it is pliable it is placed or draped over the plug.

  2. The yoke is then pressed down over the plug and is held in position by attaching g-cramps until the plastic sheet cools and 'freezes' in the newly formed shape.

  3. The plastic can then be removed and the edges can be trimmed and edge treated.

  4. The image in this unit shows the finished plastic tray.

The plug and yoke cramped in position


The finished press-formed product