10.1 A two-start square thread with a 5 mm pitch must be cut on a lathe. The crest diameter of the thread is 82 mm and the clearance angle 3°. Calculate the following: 10.1.1 The lead of the thread 10.1.2 The helix angle of the thread 10.1.3 The leading tool angle 10.1.4 The following tool angle 10.2 The measurement of a screw thread is given as M24 x 2,5. What does the following mean: 10.2.1 M 10.2.2 24 10.2.3 2,5 NSC 10.3 FIGURE 10.3 below shows a left-hand square screw thread cutting tool. Label angles A–D.

NSC Mechanical Technology Fitting and Machining ISO metric V tread: 10.1 A two-start square thread w

10.1 A two-start square thread with a 5 mm pitch must be cut on a lathe - NSC Mechanical Technology Fitting and Machining - Question 10 - 2018 - Paper 1

Question 10

10.1 A two-start square thread with a 5 mm pitch must be cut on a lathe. The crest diameter of the thread is 82 mm and the clearance angle 3°. Calculate the followi... show full transcript

Worked Solution & Example Answer:10.1 A two-start square thread with a 5 mm pitch must be cut on a lathe - NSC Mechanical Technology Fitting and Machining - Question 10 - 2018 - Paper 1

Step 1

10.1.1 The lead of the thread

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Answer

To calculate the lead of the thread, we use the formula:

Lead = pitch × number of starts

Given:

Pitch = 5 mm
Number of starts = 2

Calculating:

Lead = 5 mm × 2 = 10 mm

Step 2

10.1.2 The helix angle of the thread

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Answer

The helix angle (φ) can be calculated using:

an(φ) = \frac{lead}{pitch \times circumference}

Where circumference for an outside diameter (D) can be calculated as:

\text{Circumference} = \pi D = \pi (82 - 2.5) \\= \\ 79.67 mm

Thus, substituting values:

an(φ) = \frac{10}{79.67} \\φ = 2.29° \\(2°17'24")

Step 3

10.1.3 The leading tool angle

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Answer

The leading tool angle can be found using:

$\text{Leading tool angle} = 90° - (\text{helix angle} + \text{clearance angle})$

Given:

Helix angle = 2.29°
Clearance angle = 3°

Calculating:

$\text{Leading tool angle} = 90° - (2.29° + 3°) = 84.71° \\(84°42'36")$

Step 4

10.1.4 The following tool angle

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The following tool angle can be calculated using:

$\text{Following tool angle} = 90° - (\text{helix angle} - \text{clearance angle})$

Given:

Helix angle = 2.29°
Clearance angle = 3°

Calculating:

$\text{Following tool angle} = 90° - (2.29° - 3°) = 89.29° \\(89°17'24")$

Step 5

10.2.1 M

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Answer

The 'M' indicates it is a metric screw thread.

Step 6

10.2.2 24

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The number '24' refers to the nominal diameter of the screw thread measured in millimeters.

Step 7

10.2.3 2,5

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'2,5' represents the pitch of the thread, given in millimeters.

Step 8

10.3 A – Helix angle

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Label A represents the helix angle.

Step 9

10.3 B – Clearance angle

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Answer

Label B indicates the clearance angle.

Step 10

10.3 C – Leading tool angle

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Answer

Label C corresponds to the leading tool angle.

Step 11

10.3 D – Following tool angle

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Answer

Label D denotes the following tool angle.

10.1 A two-start square thread with a 5 mm pitch must be cut on a lathe - NSC Mechanical Technology Fitting and Machining - Question 10 - 2018 - Paper 1

Worked Solution & Example Answer:10.1 A two-start square thread with a 5 mm pitch must be cut on a lathe - NSC Mechanical Technology Fitting and Machining - Question 10 - 2018 - Paper 1

10.1.1 The lead of the thread

10.1.2 The helix angle of the thread

10.1.3 The leading tool angle

10.1.4 The following tool angle

10.2.1 M

10.2.2 24

10.2.3 2,5

10.3 A – Helix angle

10.3 B – Clearance angle

10.3 C – Leading tool angle

10.3 D – Following tool angle

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