The experiment to measure the diameter and thickness using screw gauge: Step-by-Step Guide

Screw gauge measurement:Objective

To measure the diameter of a given wire,the thickness of a sheet,and to understand the working and precision of the screw gauge.

Screw gauge measurement:Materials Required

Screw gauge

Wire

Metal sheet

Notebook for recording measurements

Screw gauge measurement: Principle

A screw gauge works on the principle of a screw thread movement. Each rotation of the screw advances or retracts the spindle by a fixed amount, called the pitch of the screw. 

Key Terms:

Pitch (P): 

Pitch is the axial distance between threads and the distance the thread moves with 360-degree revolution.In most cases, it turns out that the pitch is 1 mm.

Least Count (LC):

The least count of a measuring instrument is the smallest measurement increment that it can accurately measure. For a screw gauge, this is determined by the pitch of the screw and the number of divisions on its circular scale.

Screw Gauge measurement: Formula

Screw Gauge measurement:Thoery

The Screw Gauge: A Tool of Microscopic Precision

What is a Screw Gauge?

A screw gauge is a very accurate tool for measuring microscopic dimensions. It is made up of a thimble, a ratchet, a screw mechanism, and a U-shaped frame. The screw gauge is a vital instrument in labs and workshops since it can measure dimensions as small as 0.01 mm or even 0.001 mm.

The screw gauge, sometimes referred to as the micrometer screw gauge, is one of the most dependable instruments for reaching this level of accuracy. In this experiment, we will explore the intriguing method of measuring a wire’s diameter and a sheet’s thickness using a screw gauge. Prepare yourself for an adventure where every micron matters!

Screw Gauge measurement: Key Components of a Screw Gauge

Frame:

Frame is U-shaped, provides stability and houses the anvil and spindle.

Anvil :

The smaller stud is known as the anvil.The anvil is the fixed part of the device.

Spindle:

The longer stud is known as the spindle. The spindle moves as and when the head is moved. The object to be measured is held between the anvil and the spindle.

Sleeve:

The Barrel or sleeve is connecting the frame to the cylindrical tube. It is a non-movable part of the screw gauge and has a scale inscribed over it which is the main scale of the device.

Thimble:

The thimble carries the Vernier or secondary also called the circular scale.

Main Scale and Circular Scale: 

The main scale is on the sleeve, while the circular scale is on the thimble.

Ratchet:

It is a limiting device which applies a pressure by slipping at a predetermined torque and thus prevents the spindle from moving further.

Screw gauge measurement : Procedure

Understanding the Scales

Main Scale or Pitch scale:

Measures in millimeters (mm).

Circular Scale 0r Head scale:

Measures in fractions of a millimeter, typically 0.01 mm per division.

Measuring Zero Error:

Zero Error Correction

Step 1:: Close the jaws of the screw gauge by rotating the ratchet until it clicks.

Step 2: Observe the zero mark on the circular scale. If it doesn’t align with the reference line, note the zero error.

Positive Zero Error: The zero mark is below the reference line.

Negative Zero Error: The zero mark is above the reference line.

Step 3: Adjust subsequent measurements by subtracting or adding the zero error.

Positive error in screw gauge

Negative Error in Screw Gauge:

Determining Pitch and Least Count in a screw gauge:

Pitch of a screw gauge:

Least count of a screw gauge:

Screw Gauge Measurement: Measuring the Diameter of the Wire

Step 1: Place the wire between the anvil and spindle.

Step 2: Rotate the thimble until the wire is gently held (but not deformed).

Step 3: Read the Pitch/Main scale reading (PSR) just before the edge of the thimble.

Step 4: Read the circular/head scale reading (HSR) where it aligns with the reference line.

Step 5: Calculate the total reading using the formula

Screw Gauge Measurement :Measuring the Thickness of the Sheet

Step 1: Place the sheet between the anvil and spindle.

Step 2: Rotate the thimble until the sheet is gently held.

Step 3: Follow the same steps as above to record the PSR and HSR.

Step 4: Calculate the total reading using the same formula (Given above).

	Zero error	+3 div		Zero correction	-3 div
S.No.	Pitch scale  reading {P.S.R)	Coinciding  head scale division(H.S.D)	Head Scale Reading H.S.R =H.S.D x L.C	Thickness (Observed)  P.S.R+H.S.R	Corrected reading (P.S.R + H.S.R)Z.C
	mm	div	mm	mm	mm
1.	2.5	35	0.35	2.85	2.82
2.	2.5	34	0.34	2.84	2.81
3.	2.5	36	0.36	2.86	2.83
4.	2.5	34	0.34	2.84	2.81
5	2.5	35	0.35	2.85	2.82

Screw gauge measurement : Result

The diameter of the wire = 0.50 mm

The thickness of the sheet =2.818 mm

Conclusion: Mastering the Art of Precision

By following this detailed procedure, you’ve successfully measured the diameter of a wire and the thickness of a sheet with remarkable accuracy. The screw gauge, with its intricate design and precise measurements, is a testament to human ingenuity in the pursuit of perfection. Whether you’re a student, a scientist, or an engineer, mastering this tool opens up a world of possibilities where every micron matters.

Screw gauge measurement: Precautions

Ensure the screw gauge moves smoothly and is free from dust or rust.

Avoid excessive pressure when measuring to prevent deformation.

Take multiple readings at different points and average them for accuracy.

Correct for zero error in all calculations.

Link to this experiment

Zero error in screw gauge

Least count of a screw gauge