# Make your own pencil case

## Project

Would you like a personalised pencil case which is exactly the right size for the number of pens, pencils, etc, you generally carry around? Then make your own!

You'll need to think through some initial questions before you start planning your design:

- How long is the longest pen, pencil, ruler or other object you might want to carry in it?
- How many pens, pencils, etc, do you want to carry about?
- If you bunch then all together, and measure round them with a piece of string, what diameter pencil case do you need?

When you've decided on the dimensions of your pencil case, have a think about what shape would be a good idea. You may well decide that a cylinder, cuboid or triangular, hexagonal or octagonal prism would work well.

What does the net of the shape you want look like?

- How many separate pieces do you need?
- What shape is each piece?
- Which sides need to fit together?

Try modelling the net of your pencil case with scrap paper, folding the paper net into shape and sticking it together with sellotape. Does it work? Is it the right size for your pens and pencils?

Once you're happy with your paper prototype, you need to decide what materials you will use for the real thing:

- Does it need to be a rigid material or could you use recycled fabric?
- Will you need to alter the measurements in your design to use the chosen material?
- Do you want the same material for all the pieces, or could the ends be made of something different from the rest?
- How will you stick or fasten the pieces together?
- How will you do up the pencil case?
- Do you want to put a design on any of the pieces before making up the pencil case?
- How will you ensure your pencil case stays shut?

## Teachers' Resources

### Why do this?

The KS3 DT curriculum requires students to be able to design for themselves from their own experience or for clients, learning appropriate skills in working with different materials. This task provides a context for this which can also be linked to the KS3 maths curriculum, drawing nets in 2-d which can be folded up into 3-d objects.

#### What are the big ideas?

- Designing an item which is fit for purpose by making a paper prototype.
- Visualising what a 3-d object will look like as a 2-d net.

### Possible approach

Creating 3-d objects from a 2-d design or plan is a topic covered in both maths and DT thus providing a good context for cross-curricular work. The pencil case could be initially designed in DT, focusing on the design process. At a convenient point later, the net could be drawn and tested in maths through making a paper prototype. The design would then be taken back into the DT lesson for making the final product, covering issues such as appropriate materials and the skills necessary to work with them.

Have a collection of cardboard boxes available for students to use to stimulate ideas and to help them with making the link between the 3-d object they want to finish up with, and the 2-d net.

#### What do you need to know if you're not a maths specialist?

The net of a prism (which is a 3-d shape with a constant cross-sectional area) consists of two end pieces which determine the shape of the prism (so circles for a cylinder, squares for a cuboid, hexagons for a hexagonal prism, etc) and a rectangle. The rectangle is wrapped round the two end pieces.

This means that the rectangle needs to have a length equal to the perimeter of the end pieces. Students will know how to find the perimeter of a square. Finding the perimeter (circumference) of a circle is covered in KS3, but it would be as well to check when this topic is covered at your school. Perimeters of other shapes, such as triangles, hexagons and octagons is best done by accurate measurement at this stage.

There are techniques for drawing a regular triangle (equilateral) and hexagon. To draw an equilateral triangle or a regular hexagon, start with a circle, marking one vertex. Keeping the compasses set to the same radius, put the point on the marked vertex and make two marks on the circle on either side. Repeat with one of the new marks, and continue until there are 6 equally spaced marks around the circle. Join all 6 marks to make a hexagon, join alternate marks to make a triangle. The most straight-forward way to draw an octagon (which will then not be regular, since the sides will not all be the same length) is to use squared paper.

### Where are the possible misconceptions?

Some students will see very quickly what shapes need to be put together to make a cylinder or a prism with a polygonal cross-section, others will struggle to see the relationship between the 3-d object they want and the 2-d net. Providing a collection of cardboard boxes in different sizes and shapes which they can open out will help with this.

Even when they have worked out what shape pieces they require, some will struggle with working out which lengths need to be equal. Again a collection of boxes which they can measure will help.

### Key questions

What shapes does the net of your pencil case need to have?

What dimensions should each shape be?

How will you add 'tabs' in the material you are making it from so that you can join pieces together?

### Possible extension

Students could be encouraged to choose a more 'difficult' shape, such as the octagonal prism.

### Possible support

Let students take cardboard boxes of different shapes apart, so they can see what shape pieces they are made of, and how the different edges of the individual pieces fit together.