A triple-start square threaded bar needs to be manufactured. The lead of the square thread is 36 mm and the crest diameter is 70 mm. The clearance angle must be 3°. Calculate the following: 10.1.1 Pitch 10.1.2 Pitch diameter 10.1.3 Helix angle of the thread 10.1.4 Leading angle 10.1.5 Following angle FIGURE 10.2 below shows a cutting tool to cut screw thread. Answer the questions that follow. 10.2.1 Identify the type of screw thread. 10.2.2 Label A–D. 10.3 State the included angle for a metric V-screw thread.

NSC Mechanical Technology Fitting and Machining Screw cutting: A triple-start square threaded b

A triple-start square threaded bar needs to be manufactured - NSC Mechanical Technology Fitting and Machining - Question 10 - 2022 - Paper 1

Question 10

A triple-start square threaded bar needs to be manufactured. The lead of the square thread is 36 mm and the crest diameter is 70 mm. The clearance angle must be 3°. ... show full transcript

Worked Solution & Example Answer:A triple-start square threaded bar needs to be manufactured - NSC Mechanical Technology Fitting and Machining - Question 10 - 2022 - Paper 1

Step 1

10.1.1 Pitch

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Answer

The pitch of a square threaded bar can be calculated using the formula:

Pitch = \frac{Lead}{Number \; of\; starts}

Given:

Lead = 36 mm
Number of starts = 3

Thus,

Pitch = \frac{36\, mm}{3} = 12\, mm

Step 2

10.1.2 Pitch diameter

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Answer

The pitch diameter (D_p) can be calculated using the formula:

D_p = OD - \frac{P}{2}

Where:

OD = 70 mm
P = Pitch = 12 mm

Therefore,

D_p = 70\, mm - \frac{12 \; mm}{2} = 64\, mm

Step 3

10.1.3 Helix angle of the thread

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Answer

The helix angle (θ) can be determined using the formula:

\tan(θ) = \frac{Lead}{\pi \times PD}

Substituting the given values:

Lead = 36 mm
Pitch Diameter (PD) = 64 mm

Thus,

\tan(θ) = \frac{36}{\pi \times 64} \\ θ = \arctan(0.179049311) \approx 10.15° \text{ or } 10°9'

Step 4

10.1.4 Leading angle

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Answer

The leading angle can be calculated using:

Leading\; angle = 90° - (helix \; angle + clearance \; angle)

Given:

Helix angle ≈ 10.15°
Clearance angle = 3°

Therefore,

Leading\; angle = 90° - (10°9' + 3°) = 76°51' \text{ or } 76.85°

Step 5

10.1.5 Following angle

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Answer

The following angle can be calculated using:

Following\; angle = 90° + (helix \; angle - clearance \; angle)

Thus,

Following\; angle = 90° + (10°9' - 3°) = 97°9' \text{ or } 97.15°

Step 6

10.2.1 Identify the type of screw thread

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Answer

The screw thread is identified as a square thread.

Step 7

10.2.2 Label A–D

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Answer

A - Clearance angle B - Leading angle C - Following angle D - Helix angle

Step 8

10.3 State the included angle for a metric V-screw thread

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Answer

The included angle for a metric V-screw thread is 60°.

A triple-start square threaded bar needs to be manufactured - NSC Mechanical Technology Fitting and Machining - Question 10 - 2022 - Paper 1

Worked Solution & Example Answer:A triple-start square threaded bar needs to be manufactured - NSC Mechanical Technology Fitting and Machining - Question 10 - 2022 - Paper 1

10.1.1 Pitch

10.1.2 Pitch diameter

10.1.3 Helix angle of the thread

10.1.4 Leading angle

10.1.5 Following angle

10.2.1 Identify the type of screw thread

10.2.2 Label A–D

10.3 State the included angle for a metric V-screw thread

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