A machinist in a milling workshop is tasked to cut a spur gear with 180 teeth and a module of 2.5 - NSC Mechanical Technology Fitting and Machining - Question 6 - 2023 - Paper 1

The dedendum can be calculated using:

$ext{Dedendum} = 1.157 imes m$

Substituting the value of m:

$ext{Dedendum} = 1.157 imes 2.5 = 2.89 ext{ mm}$

The outside diameter can be calculated using:

$OD = PCD + 2(m)$

Substituting the values we found:

$OD = 450 + 2(2.5) = 455 ext{ mm}$

To find the maximum width (W) of the dovetail, we first need to calculate DE or y:

Using the triangle method:

$an heta = \frac{DE}{AD}$

Given:

• AD = 50
• $\tan(60^\circ) = \sqrt{3}$

Calculating DE:

$DE = \tan(60) imes 50 = 50 \times \sqrt{3} = 28.87 ext{ mm}$

Now calculating W:

$W = 136 + 2(DE) = 136 + 2(28.87) = 193.74 ext{ mm}$

To find the distance m, we first need to calculate AC or x:

Using the angle method:

$\tan \alpha = \frac{BC}{AC}$

Given:

• AC = 10
• $\tan(30^\circ) = \frac{1}{\sqrt{3}}$

Calculating:

$AC = \tan(30) imes 10 = 17.32 ext{ mm}$

Now calculating m:

$m = W - 2(AC + R) = 193.74 - 2(17.32 + 10) = 139.10 ext{ mm}$

To calculate the indexing required:

Using the formula:

$ext{Indexing} = \frac{A}{N}$

Where:

• A = divisions = 40
• N = number of teeth = 89

Calculating:

$ext{Indexing} = \frac{40}{89} \approx 0.4494$

Hence,

• Indexing required: 0 full turns and 24 holes on a 54-hole circle.

If we consider:

$D_r \text{ and } D_n = \frac{(A-n) \times 40}{A}$

Where:

• A = 40
• n = 89

Calculating:

$D_r = 1 \text{ and } D_n = \frac{40}{90}$

So, change gears will be:

$\frac{D_r}{D_n} = \frac{32}{72} = \frac{4}{9}$

1. Requires specialised machinery: The process of balancing workpieces often necessitates specific types of machinery, making it expensive and limiting its use to specialized workshops.

2. Difficult to ascertain the exact point of unbalance: Without precise measurement tools, it can be challenging to determine the exact unbalanced point, which could lead to inefficiency and inaccuracies in the final product.