Screw gauge

Screw gauge

Aim:

To determine the thickness of the beam or diameter of a thin wire.

Apparatus required:

Screw gauge, given beam or thin wire etc

Formula:

 Procedure:

        Prior to conducting any measurements, it is essential to determine the zero error of the screw gauge. In an accurate screw gauge, the centre line of the pitch scale should align precisely with the zero mark of the head scale. Any misalignment results in an error known as zero error, which can manifest as either positive or negative, contingent upon the position of the head scale relative to the centre line.

A positive error occurs when the zero mark of the head scale is situated below the centre line, while a negative error arises when it is positioned above the centre line.

It is crucial to ensure that only the ratchet is turned until the spindle makes contact with the anvil, a process that can be verified by the sound produced by the instrument. Once the zero error has been identified, it must be corrected accordingly. In cases of positive error, the correction applied should be the negative equivalent of the identified error value.

Subsequently, the object whose thickness or diameter is to be measured should be placed between the spindle and the anvil. Afterward, rotate the ratchet and record the readings from both the pitch scale and the head scale divisions.

Tabular Column 1: To find the thickness or diameter of a given material

Least count (LC) = 0.01 mm

Zero error = ______ div                                Zero correction = ______ div

S.No	PSR mm	HSC div	CHSC= HSC+ZC div	CHSR=CHSC x LC mm	TR=PSR+CHSR cm
1
2
3
4
5

Average =________ mm

PSR - Pitch scale reading

HSC - Head scale coincidence

CHSC - Corrected head scale coincidence

CHSR - Corrected head scale reading

Result: 

The thickness of a given beam or diameter of a thin wire using screw gauge is determined as  ______ x 10-3 m.

You can simulate screw gauge from here Virtual lab