When a broken gear was measured, it was found to have an outside diameter of 112 mm - NSC Mechanical Technology Automotive - Question 5 - 2016 - Paper 1

The pitch-circle diameter (PCD) can be found using the formula:

$PCD = OD - 2 \times m$

Substituting the values:

$PCD = 112 - 2 \times 4 = 112 - 8 = 104 \ mm$

The cutting depth is determined using the formula:

$Cutting\ Depth = m \times 2.157$

Substituting the value for the module:

$Cutting\ Depth = 4 \times 2.157 = 8.628 \ mm$

The addendum can be calculated using the module:

$Addendum = m = 4 \ mm$

The dedendum can be calculated as:

$Dedendum = 1.157 \times m$

Thus:

$Dedendum = 1.157 \times 4 = 4.628 \ mm$

The clearance is calculated using:

$Clearance = 0.157 \times m$

Therefore:

$Clearance = 0.157 \times 4 = 0.628 \ mm$

The number of teeth (T) can be found with the formula:

$T = \frac{PCD}{m}$

Substituting the previously calculated values:

$T = \frac{104}{4} = 26 \ teeth$

The indexing can be calculated using:

$Indexing = \frac{40}{n} \times 13$

Using previously calculated values:

$n = 26 \rightarrow Indexing = \frac{40}{26} \times 13 \approx 20.0$

1. Set up the work piece in the lathe: Secure the work piece and turn to the major diameter of the thread.

2. Set the compound slide angle: Adjust the compound slide to 30 degrees to the right and set the tool accurately in the post.

3. Consult index plate for correct settings: Use the quick-change gearbox to set 2 mm pitch and move accordingly.

4. Initiate cutting: Start the lathe and touch the cutting tool to the work piece.

5. Adjust feed rate: Move the tool a short distance to set the zero point on the feed dial, then engage the half-nut lever to continue.

6. Monitor progress: Use the thread gauge to check if the thread pitch is correct, ensuring successive cuts bring the thread to the desired depth.

7. Finish the cut: Stop the lathe once the threading is complete and check the thread with a ring gauge for accuracy.