5.1 State TWO advantages of using the tailstock set-over method to cut an external taper on the centre lathe. 5.2 An 85 mm long external taper, with a large diameter of 60 mm and a small diameter of 28 mm, needs to be cut on a centre lathe. Calculate the angle at which the compound slide must be set to cut this taper. 5.3 State TWO uses of the centre gauge when cutting screw thread on a centre lathe. 5.4 Calculate the length of a parallel key suitable for a 42 mm diameter shaft. 5.5 State TWO advantages of up-cut milling. 5.6 State TWO disadvantages of down-cut milling. 5.7 State TWO methods of centring a milling cutter to the axis of a work piece.

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

Question 5

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5.1 State TWO advantages of using the tailstock set-over method to cut an external taper on the centre lathe. 5.2 An 85 mm long external taper, with a large diamete... show full transcript

Worked Solution & Example Answer:5.1 State TWO advantages of using the tailstock set-over method to cut an external taper on the centre lathe - English General - NSC Mechanical Technology Fitting and Machining - Question 5 - 2018 - Paper 1

Step 1

State TWO advantages of using the tailstock set-over method to cut an external taper on the centre lathe.

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Answer

The method allows for the accurate cutting of long tapers, ensuring that the dimensions meet specifications.
Using the tailstock enables the use of an automatic feed mechanism, resulting in a smoother finish and reducing manual effort.

Step 2

Calculate the angle at which the compound slide must be set to cut this taper.

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Answer

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: $\theta \approx 10.66^{\circ}.$

Step 3

State TWO uses of the centre gauge when cutting screw thread on a centre lathe.

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Answer

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

Step 4

Calculate the length of a parallel key suitable for a 42 mm diameter shaft.

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Answer

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

Step 5

State TWO advantages of up-cut milling.

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Answer

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

Step 6

State TWO disadvantages of down-cut milling.

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Answer

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

Step 7

State TWO methods of centring a milling cutter to the axis of a work piece.

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Answer

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

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