5.1 State TWO advantages of using the tailstock set-over method to cut an external taper on the centre lathe - NSC Mechanical Technology Fitting and Machining - Question 5 - 2018 - Paper 1

To find the angle, we can use the formulas provided:

Let:

• D = Large diameter = 60 mm
• d = Small diameter = 28 mm
• L = Length of taper = 85 mm

Calculate X: $X = \frac{D - d}{2} = \frac{60 - 28}{2} = 16 \text{ mm}$

Now, calculate the angle theta: $\tan \left( \frac{\theta}{2} \right) = \frac{X}{L} = \frac{16}{85}$ $\theta = 2 \times \tan^{-1} \left( \frac{16}{85} \right)$

Using a calculator, we get: $\theta \approx 10.66^{\circ}.$

1. The centre gauge is used to measure the angle of the screw cutting tool to ensure it is set correctly for thread cutting.
2. It helps in setting the cutting tool square and perpendicular to the work piece axis, ensuring accurate thread dimensions.

The length of the parallel key can be calculated using the formula: $\text{Length} = 1.5 \times \text{diameter} = 1.5 \times 42 = 63 \text{ mm}.$

1. Up-cut milling allows for deeper cutting, which reduces cutting pressure on the tool and leads to a smoother operation.
2. It absorbs cutting pressure at the back of the edge, which enhances tool longevity.

1. Vibration in the arbor is unavoidable, which can lead to reduced precision.
2. A fine feed must be used, making the process slower and possibly less efficient.

1. The square and ruler method can help ensure the cutter is aligned correctly with the work piece.
2. The set-over method can be enhanced using the machine's dial indicator to verify alignment.