10.1 A two-start square threaded bar needs to be manufactured - NSC Mechanical Technology Fitting and Machining - Question 10 - 2021 - Paper 1

The helix angle (θ) can be found using the relationship:

an(θ) = rac{ ext{lead}}{ ext{circumference}}

In this case, the lead is 40 mm and the circumference is given by:

C = D_{m} imes rac{ ext{π}}{N} = 84 imes rac{ ext{π}}{2} = 42 ext{π} ext{ mm}

Therefore,

an(θ) = rac{40}{42 ext{π}}

Calculating θ:

ightarrow θ ext{ is approximately } 9.63°$$ Thus, the helix angle is approximately **9.63°**.

The leading tool angle can be determined using the formula:

$ext{Leading Tool Angle} = 90° - ext{Helix Angle} - ext{Clearance Angle}$

Substituting the values:

• Helix Angle = 9.63°
• Clearance Angle = 3°

This gives:

$ext{Leading Tool Angle} = 90° - 9.63° - 3° = 77.37°$

Thus, the leading tool angle is 77.37°.

The following tool angle can be calculated using:

$ext{Following Tool Angle} = 90° - ext{Helix Angle} + ext{Clearance Angle}$

Using our previous values:

• Helix Angle = 9.63°
• Clearance Angle = 3°

Therefore:

$ext{Following Tool Angle} = 90° - 9.63° + 3° = 83.37°$

Thus, the following tool angle is 83.37°.

The labels for the figure are as follows:

• A: Crest
• B: Flank
• C: Root
• D: Thread Depth

Two uses of a square thread include:

1. Mechanical Clamping: Used in clamps and vices where high friction is essential to hold the workpiece.
2. Lead Screws: Employed in devices that require linear motion, such as CNC machines, to convert rotational motion into linear movement.