a) Answer any three of the following: (i) Identify any two lubricating materials used in engineering machines; (ii) Distinguish between the use of a plug gauge and the use of a gap gauge; (iii) State two uses for a chuck guard on the lathe; (iv) Distinguish between countersink and counterbore holes; (v) Name two important properties of cutting tool materials - Leaving Cert Engineering - Question 7 - 2015

A Plug Gauge is used to check if a hole's diameter falls within a specific range by inserting a precisely sized plug into the hole. Conversely, a Gap Gauge is employed to measure the gap or space between two surfaces, ensuring that an external diameter meets required tolerances.

Two uses for a chuck guard on the lathe are:

• Protecting Operators: The guard prevents loose clothing or fingers from getting caught in the revolving chuck, enhancing safety.
• Interlocking Safety: The guard ensures that the lathe cannot be operated until the guard is in place, reducing the risk of accidents.

Surface grinding is a machining process used to produce smooth and flat surfaces. In this process, the grinding wheel rotates and the cylinder head is held on a magnetic chuck, which secures it in place. The table containing the cylinder head moves horizontally, and the grinding wheel is lowered to grind each surface until it achieves the desired smoothness.

The two safety hazards associated with the use of a grinding machine are:

• Flying Debris: Grinding processes can produce small metal particles that may be emitted at high speeds, posing a risk of eye injury. Thus, wearing protective eyewear is critical.
• Vibration Risks: Grinding machines that operate at high speeds must be correctly mounted to prevent increased vibration, which can lead to operational instability and potential injuries.

The metal cutting chips are:

• Chip A (Continuous Chip): This type of chip is typically produced from soft, ductile materials like aluminum, characterized by its long, continuous strands, indicating a smooth cutting action.
• Chip B (Discontinuous Chip): This chip is created from brittle materials, such as brass, and appears in shorter segments. This indicates a more aggressive cutting action, often leading to poor surface finishes.

The chip formation shown at C may represent a built-up edge chip condition. As the edge builds up, it can affect safety and surface finish by:

• Safety Impact: The lack of a clean cutting edge can lead to unpredictable chip behavior, posing a risk of injury to operators as chips may break loose suddenly.
• Surface Finish Impact: With a compromised cutting edge, the surface finish may suffer, resulting in a rough, uneven surface that requires additional machining or finishing processes to achieve the desired smoothness.

Advantages:

• High Consistency and Accuracy: CNC machines produce components with high precision, ensuring uniformity across batches.
• Automation and Efficiency: CNC machining reduces the need for manual labor, allowing for faster production times.

Disadvantages:

• High Initial Costs: CNC machines can be expensive to purchase and maintain compared to manual machines.
• Complex Programming: The programming aspect of CNC machines may require skilled labor, increasing operational costs for businesses.