Stock forms, types and sizes

Introduction to Stock Forms, Types, and Sizes

Welcome! In this chapter, we are going to look at Stock Forms. You might be wondering, "What on earth is a stock form?" Well, think about when you go to a supermarket to buy milk. It usually comes in 1-pint, 2-pint, or 4-pint bottles. It doesn't come in "any size you feel like." This is because standard sizes make things easier to transport, store, and sell.

In Design and Technology, stock forms are the standard shapes and sizes that materials (like wood, metal, and plastic) are sold in. Learning these is important because it helps you calculate how much material you need and helps you design products that fit the materials available, which saves money and reduces waste!

Why do we use Stock Forms?

Imagine if every time you wanted a piece of wood, the shop had to cut it from a random tree trunk just for you. It would be very expensive!
Standardization (making things to a set size) is great because:

• It makes materials cheaper because they are mass-produced.
• It makes them easier to transport and store in warehouses.
• Designers everywhere know exactly what sizes they can work with.

1. Papers and Boards

Paper and board are sold in several ways. If you've ever used a printer, you already know the most famous stock form: A4!

Common Stock Forms:

• Sheet: Flat pieces (like a piece of paper).
• Roll: Long continuous lengths (like wallpaper or wrapping paper).
• Ply: Layers of paper glued together to make it stronger.

How they are sold:

- Size: Usually follows the "A" series (A0 is the biggest, A4 is standard, A5 is half of A4).
- Weight: Measured in GSM (Grams per Square Metre). The higher the GSM, the heavier and thicker the paper.
- Thickness: Measured in microns. 1000 microns = 1mm.

Standard Components: These are the "extras" you use with paper, like fasteners, seals, and bindings (like the spiral on a notebook).

Quick Review: Remember that as the "A" number gets bigger (e.g., A4 to A5), the paper size actually gets smaller!

2. Timber Based Materials (Wood)

Wood doesn't just come as "a log." It is processed into specific shapes so builders and designers can use it easily.

Common Stock Forms:

• Planks and Boards: Long, flat pieces of wood used for flooring or furniture.
• Standard Moldings: These are shaped strips of wood, like skirting boards or picture frames.

How they are sold:

Timbers are sold by length, width, thickness, and sometimes diameter (for round dowels). If you go to a DIY shop, you might see "2 by 4" — this refers to the thickness and width in inches (though we usually use millimetres in school!).

Standard Components: Things like woodscrews, hinges, and KD (Knock-Down) fittings. KD fittings are those plastic blocks and bolts you find in IKEA furniture that allow you to put it together easily at home.

3. Metal Based Materials

Metals are very versatile and come in many "profiles" (cross-section shapes).

Common Stock Forms:

• Sheet: Thin, flat sections.
• Rod: Solid cylinders of metal.
• Bar: Solid flat or square lengths.
• Tube: Hollow cylinders (like a bike frame).

How they are sold:

Metals are sold by length, width, thickness, and diameter. For tubes, the wall thickness is also very important!

Standard Components: To join metal, we use rivets, machine screws, nuts, and bolts.

4. Polymers (Plastics)

Since plastic is man-made, it can be formed into almost any stock shape imagineable.

Common Stock Forms:

• Sheet, Rod, and Tube: Just like metals.
• Powder and Granules: These are used in factories. They are melted down to be injection molded into shapes like LEGO bricks.
• Foam and Films: Think of expanded polystyrene or thin cling-film.

How they are sold:

Polymers are sold by length, width, and gauge (another word for thickness). Granules are usually sold by weight in bags.

Standard Components: Plastics often use specialized screws, nuts, bolts, and plastic hinges.

5. Textile Based Materials

Textiles start as tiny fibres, which are turned into stock forms you can actually use.

Common Stock Forms:

• Yarns: This is "thread" or "wool" used for knitting or weaving.
• Fabrics: These are big "sheets" of material made from yarn.

How they are sold:

Fabric is almost always sold by the roll. You buy it by the width of the roll and the weight of the fabric. It is also measured by ply (the number of threads twisted together).

Standard Components: The bits that finish a garment, such as zips, press studs (poppers), and Velcro.

6. Electrical and Mechanical Components

These are the "guts" of a product that make it work.

How they are sold:

• Quantity: Usually sold in packs (e.g., a pack of 100 LEDs).
• Ratings: Sold by Volt and Current (Amp) ratings so you don't blow them up!

Standard Components:

• E12 Resistor Series: A standard set of resistor values used worldwide.
• DIL (Dual In-Line) packages: These are the little "caterpillar" shaped microchips.
• Microcontrollers (PIC): Small computers on a chip that you can program.

The Maths Bit: Calculating and Nesting

Don't worry, the maths here is very practical! Because materials come in fixed stock sizes, you need to be smart about how you cut your shapes out to avoid wasting money.

Nesting and Minimising Waste

Nesting is like using a cookie cutter on dough. You want to place your shapes as close together as possible so you don't leave big gaps of wasted material.
Analogy: Imagine you have a sheet of stickers. If the stickers are scattered everywhere, you can't fit many on. If they are lined up perfectly, you can fit dozens!

Key Formulas:

You may need to calculate the Surface Area or Volume of a stock form to know how much to buy:

Area of a rectangle: \( \text{Area} = \text{length} \times \text{width} \)

Volume of a 3D shape: \( \text{Volume} = \text{length} \times \text{width} \times \text{height} \)

Key Takeaway: Always plan your "cutting list" before buying material to make sure you use the most efficient stock form size!

Quick Review: Common Mistakes to Avoid

- Mistake: Thinking "A0" paper is the smallest.
- Correction: A0 is the biggest (1 square metre!). A4 is what you use in school.

- Mistake: Forgetting that "Tubes" are hollow and "Rods" are solid.
- Correction: Always check if your design needs to be hollow (to save weight) or solid (for strength).

Summary Checklist

1. Materials come in Stock Forms to keep costs down.
2. Paper is measured in GSM; Wood comes in Planks; Metal comes in Sheets/Tubes.
3. Standard components (like screws or zips) are designed to work with these stock forms.
4. Use Nesting to save material and help the environment!