10.1 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 10.2 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 Calculations on size of drills for bolts and nuts (Square thread): 10.1 A triple-start square threa

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

Question 10

10.1 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... show full transcript

Worked Solution & Example Answer:10.1 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

To calculate the pitch of the square thread, we use the formula:

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

Given that the lead is 36 mm and there are 3 starts:

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

Step 2

10.1.2 Pitch diameter

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Answer

The pitch diameter can be calculated with the formula:

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

Using the outer diameter (OD) of 70 mm and the pitch obtained in the previous step:

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

Step 3

10.1.3 Helix angle of the thread

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Answer

The helix angle can be found using the tangent function:

\tan(\theta) = \frac{Lead}{\pi \times PD}

Substituting the known values:

\tan(\theta) = \frac{36}{\pi \times 64} \ \theta = \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 is calculated as follows:

Leading \: angle = 90° - (Helix \: angle + Clearance \: angle)

Assuming a clearance angle of 3°:

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

Step 5

10.1.5 Following angle

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The following angle can be computed using:

Following \: angle = 90° + (Helix \: angle - Clearance \: angle)

Substituting the respective angles:

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 type is identified as a square thread.

Step 7

10.2.2 Label A–D.

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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°.

10.1 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:10.1 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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