A machine table is lifted by means of a double start screw thread which had a pitch of 5 mm. How many revolutions are needed to lift the table to a height of 200 mm?

Explanation:

Concept:

Double start screw thread:

• In the double start thread, one thread is wound exactly in the middle of the other.
• This made it possible to raise the lead of the helix without raising the pitch.
• The relation between lead and pitch is given as:

Lead (L) = pitch (p) × number of start (n)

Calculation:

Given:

Pitch (p) = 5 mm, lift (L) = 200 mm, type of thread = double start

So, for one revolution, the screw advance = 2 × p = 2 × 5 = 10 mm

Number of revolutions = \(\frac{Total\space screw\space advance}{Screw\space advance\space in\space one\space revolution}\) = \(\frac{200}{10}\) = 20 revolutions

Thus, option (1) is the correct answer.