5.1 A spur gear with 118 teeth must be cut on a universal milling machine - NSC Mechanical Technology Welding and Metalwork - Question 5 - 2017 - Paper 1

Up-Cut Milling

• In up-cut milling, the cutter rotates against the direction of the workpiece feed. This method typically pulls the material upward.

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Down-Cut Milling

• In down-cut milling, the cutter rotates in the same direction as the workpiece feed. This method pushes the material downward.

• Sketch:

  

Summary

• In up-cut milling, the cutting occurs as the chip thickness decreases, while in down-cut milling, the cutting occurs as the chip thickness increases.

To calculate the width of the key:

$\text{Width} = \frac{D}{4} = \frac{102}{4} = 25.5 \text{ mm}$

To find the thickness of the key:

$\text{Thickness} = \frac{D}{6} = \frac{102}{6} = 17 \text{ mm}$

To determine the length of the key:

$\text{Length} = D \times 1.5 = 102 \times 1.5 = 153 \text{ mm}$

To calculate the thickness at the smaller end of the key:

$\text{Thickness at smaller end} = \frac{T \cdot L}{100} = \frac{17 \cdot 153}{100} = 15.47 \text{ mm}$

The addendum (height of the tooth above the pitch circle):

$\text{Addendum} = ext{module} = 3 \text{ mm}$

The dedendum (depth of the tooth below the pitch circle):

$\text{Dedendum} = 1.25 \times ext{module} = 1.25 \times 3 = 3.75 \text{ mm}$

The clearance (space between the top of the tooth and the base of the tooth in the mating gear):

$\text{Clearance} = \text{Dedendum} - ext{Addendum} = 3.75 - 3 = 0.75 \text{ mm}$

To calculate the pitch circle diameter:

$\text{Pitch Circle Diameter (PCD)} = \text{Number of Teeth} \times ext{module} = 60 \times 3 = 180 \text{ mm}$

To find the outside diameter:

$\text{Outside Diameter} = \text{PCD} + 2 \times ext{Addendum} = 180 + 2 \times 3 = 186 \text{ mm}$

To calculate the cutting depth:

$\text{Cutting Depth} = 2.157 \text{ mm} \text{ or } 2.25 \text{ mm}$

To find the circular pitch:

$\text{Circular Pitch} = ext{module} \times \pi = 3 \times \pi \approx 9.43 \text{ mm}$