6.1 A spur gear, with a pitch-circle diameter of 165 mm and 110 teeth, is needed for a gearbox - NSC Mechanical Technology Fitting and Machining - Question 6 - 2022 - Paper 1

The outside diameter (OD) of the spur gear can be calculated using the formula:

$OD = D + 2m$

Substituting the values:

• $D = 165$ mm
• $m = 1.5$ mm

We get: $OD = 165 + 2 \times 1.5 = 168 \text{ mm}$

Therefore, the outside diameter of the spur gear is 168 mm.

To find the maximum width (W) of the dovetail, we note from the figure:

• The total width across the two circles is 120 mm
• The diameter of each circle is 30 mm

The width of the dovetail can be calculated as: $W = 120 - 2 \times 30 = 60 \text{ mm}$

Thus, the maximum width of the dovetail is 60 mm.

The distance (m) between the precision rollers can be found from the drawing as:

• The diameter of the circles is 30 mm, with 11 mm separation between their centers.

Thus: $m = 30 + 11 = 41 \text{ mm}$

Therefore, the distance between the precision rollers is 41 mm.

The indexing requires calculating the number of divisions to index the spur gear:

The formula to find the indexing (I) is: $I = \frac{T}{A}$ Where:

• $T = 163$ (number of teeth)
• $A = 160$ (divisions of the simple indexing)

Substituting: $I = \frac{163}{160} \approx 1.01875$

Thus, about 1.01875 rotations are needed in the dividing head.

For the change gears required, use the formula for calculating gear ratios:

The required ratio can be derived from: $R = \frac{T}{N}$ Where $N$ is the number of turns of the handle that correlate to the index. Assuming a direct proportionality with the given ratio: $N = \frac{A}{R} = \frac{160}{40} = 4$

Thus, 4 change gears are required.

Two types of balancing methods include:

1. Static Balancing
2. Dynamic Balancing

Static balancing focuses on balancing the object at rest. In contrast, dynamic balancing examines forces when the object is in motion.

Two advantages of balancing rotating components include:

1. Reduced Vibration: Balancing minimizes vibrations, leading to smoother operation and reduced wear.
2. Increased Lifespan: Properly balanced components tend to last longer, which reduces maintenance costs and downtime.