A spur gear has a pitch-circle diameter of 126 mm with 42 teeth - NSC Mechanical Technology Fitting and Machining - Question 6 - 2019 - Paper 1

The working depth (WD) can be calculated using the formula:

$$WD = 2 \times m$$

Where m is the module. Substituting the previously calculated module:

$$WD = 2 \times 3 \text{ mm} = 6 \text{ mm}$$

Therefore, the working depth is 6 mm.

The cutting depth can be calculated as:

$$Cutting\ depth = 2.157 \times m$$

Using the module value:

$$Cutting\ depth = 2.157 \times 3 \text{ mm} = 6.471 \text{ mm}$$

Alternatively, it can also be given in terms of:

$$Cutting\ depth = 2.25 \times m = 2.25 \times 3 \text{ mm} = 6.75 \text{ mm}$$

Thus, the cutting depth can be either 6.471 mm or 6.75 mm.

To find the required angular indexing, we use the formula:

$$Indexing = \frac{34°}{9°} = \frac{34}{9} = 3.78 \\ ext{(approximately 3 full turns with remainder)}$$

This means that after 3 full turns, the next step involves finding the corresponding hole count using the ratio:

$$N = 34° \text{ to } 9° \rightarrow 34°\ times \frac{42}{54} = 3\text{ holes} \\ ext{(for a total of 3 full turns and 42 holes on the 54 hole circle)}$$

Thus, angular indexing for this angle results in 3 full turns and 42 holes.