10.1 Draw a cross-sectional view of a square screw thread. Label the crest and the root of the screw thread. 10.2 A two-start square screw thread needs to be cut on a lathe. The lead of the thread is 25 mm and the crest diameter is 70 mm. The clearance angle must be 3°. Calculate the following: 10.2.1 Pitch diameter 10.2.2 Helix angle of the screw thread 10.2.3 Leading tool angle 10.2.4 Following tool angle 10.3 Label parts A–C of the V-screw thread shown in FIGURE 10.3 below.

NSC Mechanical Technology Fitting and Machining Calculations on size of drills for bolts and nuts (Square thread): 10.1 Draw a cross-sectional view

10.1 Draw a cross-sectional view of a square screw thread - NSC Mechanical Technology Fitting and Machining - Question 10 - 2023 - Paper 1

Question 10

10.1 Draw a cross-sectional view of a square screw thread. Label the crest and the root of the screw thread. 10.2 A two-start square screw thread needs to be cut on... show full transcript

Worked Solution & Example Answer:10.1 Draw a cross-sectional view of a square screw thread - NSC Mechanical Technology Fitting and Machining - Question 10 - 2023 - Paper 1

Step 1

10.2.1 Pitch diameter

96%

114 rated

Answer

To calculate the pitch diameter (PD), we first need to find the pitch. The pitch is given by the formula:

$\text{Pitch} = \frac{\text{Lead}}{\text{Number of starts}}$

Given:

Lead = 25 mm
Number of starts = 2

Thus,

$\text{Pitch} = \frac{25}{2} = 12.5 \text{ mm}$

Next, we apply the formula for the pitch diameter:

$\text{PD} = \text{OD} - \frac{P}{2}$

OD = 70 mm
P = 12.5 mm

Thus,

$\text{PD} = 70 - \frac{12.5}{2} = 70 - 6.25 = 63.75 \text{ mm}$

Step 2

10.2.2 Helix angle of the screw thread

99%

104 rated

Answer

To calculate the helix angle (θ), we use the formula:

$\tan(\theta) = \frac{\text{Lead}}{\pi \times D_p}$

Substituting the values:

Lead = 25 mm
Pitch diameter (D_p) = 63.75 mm

Thus,

$\tan(\theta) = \frac{25}{\pi \times 63.75}$

Calculating gives:

$\theta = \tan^{-1}(0.124827406) \approx 7.12° \text{ or } 7°$

Step 3

10.2.3 Leading tool angle

96%

101 rated

Answer

The leading angle can be calculated from the helix angle and the clearance angle:

$\text{Leading angle} = 90° - (\text{Helix angle} + \text{Clearance angle})$

Substituting the values:

Helix angle = 7.12°
Clearance angle = 3°

Thus,

$\text{Leading angle} = 90° - (7.12° + 3°) = 90° - 10.12° = 79.88° \text{ or } 79°53'$

Step 4

10.2.4 Following tool angle

98%

120 rated

Answer

The following angle can be calculated similarly:

$\text{Following angle} = 90° + (\text{Helix angle} - \text{Clearance angle})$

Substituting the values:

Helix angle = 7.12°
Clearance angle = 3°

Thus,

$\text{Following angle} = 90° + (7.12° - 3°) = 90° + 4.12° = 94.12° \text{ or } 94°$

Step 5

10.3 Label parts A–C of the V-screw thread shown in FIGURE 10.3 below

97%

117 rated

Answer

The parts of the V-screw thread are labeled as follows:

A: Helix angle
B: Pitch / Lead
C: Root

10.1 Draw a cross-sectional view of a square screw thread - NSC Mechanical Technology Fitting and Machining - Question 10 - 2023 - Paper 1

Worked Solution & Example Answer:10.1 Draw a cross-sectional view of a square screw thread - NSC Mechanical Technology Fitting and Machining - Question 10 - 2023 - Paper 1

10.2.1 Pitch diameter

10.2.2 Helix angle of the screw thread

10.2.3 Leading tool angle

10.2.4 Following tool angle

10.3 Label parts A–C of the V-screw thread shown in FIGURE 10.3 below

Join the NSC students using SimpleStudy...