5.1 Neatly sketch and label an isometric V-screw thread to indicate the following screw thread terminology on: 5.1.1 Crest, major or outside diameter 5.1.2 Included screw-thread angle 5.1.3 Screw-thread pitch 5.1.4 Screw-thread crest 5.1.5 Screw-thread flanks 5.2 Identify the milling processes indicated in FIGURES 5.2.1 and 5.2.2 below - NSC Mechanical Technology Welding and Metalwork - Question 5 - 2017 - Paper 1

This angle is the angle between the flanks of the thread. It influences the strength and fit of the screw.

The pitch is the distance between corresponding points on adjacent threads. It indicates how tightly the threads are spaced.

The crest is the top or peak of the thread. It is the highest point of the thread profile.

The flanks are the sides of the thread that connect the crest to the root. They are crucial for ensuring proper thread engagement.

The milling process in FIGURE 5.2.1 is identified as up-cut milling.

The milling process in FIGURE 5.2.2 is identified as down-cut milling.

To calculate the indexing:

$Indexing = \frac{40}{A}$

Where:

• A = 22

Calculating, we have: $Indexing = \frac{40}{22} \approx 1.818$

This means that with 1 full turn, we can achieve approximately 54 holes on the 66-hole circle.

The sector arms B and H save time and reduce the risk of errors during the indexing process.

Index plate G is equipped with a variety of accurately spaced holes, allowing for precise movements of the indexing mechanism.

The index pin A ensures correct engagement in the desired hole on the index plate, facilitating accurate rotation.

The ratio between worm gear E and gear D is 40:1.

The PCD can be calculated using the formula: $PCD = m \times T$

For a gear with 94 teeth and a module of 3: $PCD = 3 \times 94 = 282 \text{ mm}$

The outside diameter can be calculated as: $OD = PCD + 2 \times m$

Thus, $OD = 282 + 2 \times 3 = 288 \text{ mm}$

The dedendum can be calculated as: $Dedendum = 1.157m$

For m = 3: $Dedendum = 1.157 \times 3 = 3.471 \text{ mm}$

The cutting depth is given by: $Cutting depth = 2.25 m$ For m = 3: $Cutting depth = 2.25 \times 3 = 6.75 \text{ mm}$