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 Automotive - Question 5 - 2017 - Paper 1

The included angle of a screw thread is the angle formed between the flanks of the thread. This is important for the engagement of threads and affects how the screw interacts with its counterpart. Indicate this angle on the diagram.

Pitch is defined as the distance between corresponding points on adjacent threads (e.g., crest to crest or root to root). This measurement indicates how coarse or fine the threads are. Label this distance clearly on the sketch.

The crest is the top surface of the thread. It is the most outward point of the thread profile. Mark this point appropriately in the diagram.

Flanks are the sides of the thread that connect the crest to the root. They contribute to the strength and engagement of the thread. Make sure to designate these in your sketch.

The process shown in FIGURE 5.2.1 is identified as Up-cut milling. This technique involves feeding the workpiece against the rotation of the cutter, resulting in a cutting action that pulls the material upwards.

The process shown in FIGURE 5.2.2 represents Down-cut milling. In this method, the cutter rotates into the workpiece, forcing it downward, which can produce a better surface finish.

Sector arms B and H serve to hold the dividing head in place while allowing for precise angular adjustments. They help in aligning the workpiece accurately during milling operations.

The index plate G is equipped with several holes that allow for accurate indexing during milling. This enables the user to achieve specific rotational positioning of the workpiece for angle divisions.

Index pin A engages with the holes in index plate G to secure the position of the dividing head during machining. This ensures the workpiece is accurately aligned for cutting.

The ratio between worm gear E and gear D is 40:1. This indicates that for every complete turn of the worm gear, the output shaft of gear D will rotate 1/40 of a turn, providing a mechanical advantage.

The pitch-circle diameter (PCD) is calculated using the formula:

Where m is the module and T is the number of teeth. For a gear with module 3 and 94 teeth:

The outside diameter (OD) of the gear is found using the formula:

Substituting the values:

The dedendum (b) is calculated as:

For a module of 3:

The cutting depth can be calculated as:

Substituting the values: