Introduction: Why do Stock Forms Matter?

Imagine you are building a bookshelf. You wouldn't want to go into a forest, chop down a tree, and wait months for it to dry out before you could start cutting! Instead, you go to a timber merchant and buy wood that is already cut into helpful, standard shapes. These are called stock forms.

Using stock forms makes life easier for designers and manufacturers because they are standardised. This means a piece of wood bought in one shop will be the same size as a piece bought in another. It also makes it much easier to calculate costs and minimise waste.

Timber Stock Forms

In the world of timbers, wood is supplied in several common shapes and sizes. Here are the main ones you need to know for your exam:

1. Boards and Planks

This is the most common form for both natural timbers (like Oak or Pine) and manufactured boards (like MDF or Plywood). They are long, flat, and rectangular.

2. Dowels

Dowels are cylindrical rods of wood. They are often used for joining pieces of wood together, making clothes pegs, or as axles in toy cars. They come in standard diameters, such as \(5 \text{ mm}\), \(10 \text{ mm}\), or \(15 \text{ mm}\).

3. Mouldings

These are lengths of timber cut into decorative shapes, like skirting boards or picture frames. While you don't need to memorise every shape, it's important to know they are a standard way timber is sold.

Understanding Wood Sizes: Rough Sawn vs. Planed

When you buy natural timber, it starts as "Rough Sawn." This means it has been cut with a large industrial saw and feels fuzzy or "hairy" to the touch. To make it smooth and ready for a project, it needs to be planed.

Important Terminology:

  • PSE (Planed Square Edge): Only the surfaces are planed smooth, leaving the edges rough, or sometimes just one edge is planed square.
  • PAR (Planed All Round): All four sides of the timber have been planed smooth.

The "Magic" \(3 \text{ mm}\) Rule:
When a piece of wood is planed, it loses about \(3 \text{ mm}\) from its thickness and width. If you order a piece of \(25 \text{ mm}\) thick rough sawn timber and ask for it to be PAR, it will arrive measuring approximately \(22 \text{ mm}\). Designers must account for this when planning their projects!

Standard Sizes for Manufactured Boards

Manufactured boards like MDF, Plywood, and Chipboard come in very specific, large standard sheets. In the UK, we use metric measurements, but these sizes are based on old imperial (feet and inches) measurements. You must remember these two common sizes:

  • Full sheet: \(2440 \text{ mm} \times 1220 \text{ mm}\)
  • Half sheet: \(1220 \text{ mm} \times 610 \text{ mm}\)

Common thicknesses for these boards include \(3 \text{ mm}\), \(6 \text{ mm}\), \(9 \text{ mm}\), \(12 \text{ mm}\), and \(18 \text{ mm}\).

Quick Review: Why use standard sizes? It lowers the cost because machines can be set to one size, and it makes transporting and storing the wood much easier!

Calculating Material Quantities

In your exam, you will likely have to calculate how much wood you need. This is a vital skill to ensure you don't run out of material or waste money buying too much.

1. Calculating Area

To find out how much space a flat board takes up, we use the area formula:
\( \text{Area} = \text{Length} \times \text{Width} \)

Example: If you need a piece of Plywood that is \(500 \text{ mm}\) long and \(200 \text{ mm}\) wide:
\( 500 \text{ mm} \times 200 \text{ mm} = 100,000 \text{ mm}^2 \)

2. Calculating Volume

If you need to know the total "bulk" of the wood (perhaps for shipping costs), use volume:
\( \text{Volume} = \text{Length} \times \text{Width} \times \text{Thickness} \)

3. Working with Wastage

In real life, you always lose some wood to "saw kerf" (the dust created by the blade) or mistakes. We usually add a percentage for wastage, typically \(10\%\).

How to calculate \(10\%\) wastage:
If your project needs \(2 \text{ m}^2\) of wood:
1. Find \(10\%\): \( 2 \div 10 = 0.2 \)
2. Add it to the total: \( 2 + 0.2 = 2.2 \text{ m}^2 \)

Step-by-Step: How many pieces can I get?

The Problem: How many pieces of \(610 \text{ mm} \times 305 \text{ mm}\) can you cut from a standard half-sheet of MDF (\(1220 \text{ mm} \times 610 \text{ mm}\))?

Step 1: Compare the widths.
\( 1220 \text{ mm} \div 610 \text{ mm} = 2 \)

Step 2: Compare the lengths.
\( 610 \text{ mm} \div 305 \text{ mm} = 2 \)

Step 3: Multiply the results.
\( 2 \times 2 = 4 \text{ pieces} \)

Top Tip: Always sketch it out! A quick drawing of the board can help you visualise how the pieces fit and ensure you aren't forgetting the "grain direction" if using natural timber.

Key Takeaways

  • Stock forms are standard shapes like boards and dowels.
  • PAR stands for Planed All Round; it's smooth but slightly smaller than rough sawn wood.
  • Standard board sizes are \(2440 \times 1220 \text{ mm}\).
  • Always account for wastage when ordering materials.
  • Math skills like area, volume, and percentages are essential for calculation questions in Section B of your exam.