FIGURE 5.1 below shows the set-up of a taper with an included angle of 8°, to be machined between centres - NSC Mechanical Technology Fitting and Machining - Question 5 - 2019 - Paper 1

To calculate the tailstock set-over, we use the set-over angle determined in the previous calculation.

Given that the set-over can be found using the relationship:

$X = \frac{AB}{L} \times 300$

Substituting the values:

• $AB \approx 20.98 ext{ mm}$
• $L = 300 ext{ mm}$

Then,

$X = \frac{20.98}{300} \times 400 \approx 27.97 ext{ mm}$

Thus, the tailstock set-over required is approximately 27.97 mm.

To find the width of the parallel key:

$\text{Width} = \frac{D}{4}$

Given: $D = 42 ext{ mm}$,

Substituting:

$\text{Width} = \frac{42}{4} = 10.5 ext{ mm}$

The width of the key is 10.5 mm.

To find the thickness of the parallel key:

$\text{Thickness} = \frac{D}{6}$

Given: $D = 42 ext{ mm}$,

Substituting:

$\text{Thickness} = \frac{42}{6} = 7 ext{ mm}$

The thickness of the key is 7 mm.

1. A better finish is obtained due to the cutting action slicing down into the material, which reduces the friction.

2. High-speed cutting is possible, which leads to more efficient machining processes and allows for deeper cuts to be made.

To illustrate straddle milling, depict a setup with two milling cutters positioned either side of a workpiece. Ensure to label the following parts:

• Arbor
• Work piece
• Milling cutters

This setup allows simultaneous cutting on both sides of the workpiece, enhancing efficiency.