## Introduction: Casting Plaster

Making a cuboctahedron pencil holder;

## Step 1: Materials You Will Need:

- A sheet of high impact polystyrene

- A sheet of paper

- A set square

- A pencil

- A gluestick

- A compass

- A scissor

- Plaster

- Sellotape

## Step 2: Stick a Piece of Paper Onto High Impact Polystyrene

Use the glue stick to stick the paper onto the high impact polystyrene, try to stick the paper to the edge as closely as possible.

## Step 3: Draw Five 70mm Squares on the Paper

Draw five 70mm squares with a set square to make sure the angles are 90 degrees.

## Step 4: Draw Eight 70mm Triangles on the Paper With a Compass

Draw eight 70mm triangles by drawing out a 70mm line first. Then, open the compass until it is 70mm wide. Put the needle on one end of the line and mark it out, do the same on the other side. Connect each end of the line to the intersection of each line made on the compass. Repeat eight times.

## Step 5: Cut Out All the Squares and Triangles

Use a scissor to cut out all the shapes, making sure to stay as accurate to the lines as possible.

## Step 6: Assemble the Shape

Using sellotape, put together the shape, making sure to seal each edge and to have the paper be on the outside. To assemble the shape, start off with a square and stick a triangle to each side of the square. Then, stick squares to the side of each triangle, all going the same way; do the same for the triangles. Stick each shape together, making sure that the side of each triangle touches the side of a square.

## Step 7: Draw Four Rectangles and One Square on Polystyrene

Draw four 120mm x 65mm rectangles and a 60mm square on leftover polystyrene.

## Step 8: Cut Out the Rectangles and Square

Use a scissor to cut out all the shapes, making sure to stay as accurate to the lines as possible.

## Step 9: Assemble a Rectangular Prism

Use sellotape to assemble a rectangular prism, make sure to put the side with paper on the inside of the prism and to seal every edge.

## Step 10: Mix Plaster

Mix plaster by using 2 parts water and 3 parts plaster, work fast.

## Step 11: Pour the Plaster

Carefully pour the plaster into the cuboctahedron, when the plaster is a little over half of the mould, slowly insert the rectangular prism, making sure that it is centred. If the plaster isn't filled to the brim when the rectangular prism is put in, take it out and pour more plaster. Use tape to secure the rectangular prism and make sure it doesn't move. Gently tap the sides to remove air bubbles.

## Step 12: Remove the Polystyrene

After waiting for 24 hours or more for the plaster to dry, use a blade to remove the sellotape and carefully peel the polystyrene off, do the same for both the mould and core.

## Step 13: Sand Down the Sides of the Product

Sand the sides of the product down carefully until smooth.

## Comments

2 years ago

Nicely done!

There have been a lot of these shared as instructables lately - was this for a school assignment, and if so, what type of course was this for?