Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Apply appropriate safety procedures in the workshop.
• Select materials based on their properties.
• Accurately use marking-out tools.
• Develop a time management plan for the PAT.
• Interpret technical drawings.

Lesson summary

This week's focus is on preparing for the Practical Assessment Task (PAT), which is a significant component of your Grade 12 Mechanical Technology mark. Think of the PAT as your opportunity to demonstrate the skills and knowledge you’ve gained throughout the year in a tangible and practical way. Successfully completing the PAT can open doors to further education, apprenticeships, and employment in the mechanical engineering field – vital sectors for South Africa's development. It's not just about building something; it's about problem-solving, applying theory, and showcasing your craftsmanship.

Lesson notes

2.1 Workshop Safety and Personal Protective Equipment (PPE) Safety is paramount in any workshop environment. Before starting any PAT, you must understand and adhere to all safety regulations.

General Workshop Rules: Cleanliness, no running, no horseplay, reporting accidents immediately, understanding emergency procedures (fire exits, first aid).

Personal Protective Equipment (PPE): Safety Glasses/Goggles: Protect your eyes from flying debris, dust, and sparks. Always wear them.

Overalls/Aprons: Protect your clothing from dirt, oil, and sparks.

Safety Shoes/Boots: Protect your feet from falling objects and sharp materials. Steel-toed boots are ideal.

Gloves: Choose the appropriate gloves for the task (e.g., leather gloves for welding, nitrile gloves for handling chemicals).

Hearing Protection: Earplugs or earmuffs are essential when working with noisy machinery.

Dust Mask/Respirator: Protect your lungs from dust and fumes, especially when sanding, grinding, or welding.

Machine-Specific Safety: Each machine (lathe, milling machine, welding machine, drill press, etc.) has its own set of safety rules. Read the manufacturer's instructions and ask your teacher for clarification if needed. Never operate a machine you haven't been trained on.

Material Handling Safety: Use correct lifting techniques to avoid back injuries. Secure materials properly before cutting or machining. Be aware of sharp edges and hot surfaces.

Example: While operating a center lathe, one must wear safety goggles to protect from flying swarf, ensure that long hair is tied back to avoid entanglement with the chuck, and never attempt to measure or adjust the workpiece while the machine is running. 2.2 Material Selection and Properties Choosing the right material is crucial for the success and longevity of your PAT project.

Consider the following properties: Strength: Ability to withstand loads without breaking (tensile strength, compressive strength, shear strength).

Hardness: Resistance to scratching, indentation, and wear.

Toughness: Ability to absorb energy and resist fracture.

Ductility: Ability to be drawn into a wire.

Malleability: Ability to be hammered or rolled into thin sheets.

Corrosion Resistance: Ability to resist degradation due to environmental factors (rust, oxidation).

Weldability: Ease with which a material can be joined by welding.

Machinability: Ease with which a material can be cut and shaped using machine tools.

Cost: Consider the affordability and availability of the material.

Common Materials: Mild Steel: Low carbon content, relatively inexpensive, good weldability and machinability. Suitable for general-purpose applications.

High Carbon Steel: Higher carbon content, harder and stronger than mild steel, but less ductile and weldable. Used for tools and dies.

Aluminum: Lightweight, corrosion-resistant, good thermal and electrical conductivity. Used in aerospace, automotive, and construction.

Stainless Steel: Corrosion-resistant, strong, and hygienic. Used in food processing, medical equipment, and architecture.

Brass: Corrosion-resistant, good electrical conductivity, attractive appearance. Used in plumbing fixtures, decorative hardware, and musical instruments.

Plastics: Various types (e.g., PVC, ABS, Nylon), each with its own unique properties. Used in a wide range of applications.

Example: If your PAT requires a part that needs to withstand high tensile forces, you might choose high carbon steel over mild steel.

However, if weldability is a critical factor, mild steel might be a better choice. If weight is a significant concern, aluminum could be considered. 2.3 Marking-Out Tools and Techniques Accurate marking out is essential for ensuring the precision of your final product.

Common marking-out tools include: Steel Rule: For measuring straight lines and distances.

Try Square: For checking right angles and marking perpendicular lines.

Combination Square: Versatile tool for measuring, marking angles, and finding centers.

Protractor: For measuring and marking angles.

Dividers: For transferring distances and drawing circles and arcs. Punches (Center Punch, Dot Punch): For marking the center of holes for drilling and creating reference points.

Scribers: For marking lines on metal surfaces.

Surface Plate: Flat, stable reference surface for accurate marking out.

Height Gauge: For measuring heights and marking parallel lines.

Techniques: Datum Line: Establish a reference line (datum line) from which all other measurements are taken.

Accuracy: Use sharp tools and apply light pressure to avoid distorting the material.

Clarity: Make clear, visible lines that are easy to follow.

Double-Check: Always double-check your measurements before cutting or machining.

Example: To mark out a rectangular plate with dimensions 100mm x 50mm, first use a steel rule and scriber to mark a datum line along one edge of the material. Then, use a try square to mark a perpendicular line at one end of the datum line.