How to read a micrometer & also know its type,part,principle

Hello friends today we will talk about micrometer which is the part of metrology in which we will know how to read a micrometer.

Before knowing how to read a micrometer, First of all, we have to know what are these types, what are the parts of  micrometer, on which principle the micrometer works, Then we will be able to take micrometer readings with accurately.

On How to read a micrometer, You need to know about measuring technique, zero error, methods of removing zero error.

This is just a brief overview but we will know further in detail.

So let’s start step by step about micrometer and then after know, how to read a micrometer.

Definition of Micrometer

A micrometer is a device which is used to measure dimension of length, diameter, thickness with accurately.

Types of Micrometer

If we talk about the type of micrometer there are so many types of micrometer available in the market.
So here we only discuss that type of micrometer which is widely used in industries.


types of micrometer
Different Types of Micrometer


Outside Micrometer

Outside Micrometer Used to measure external dimensions.
As like outside diameter of shaft, flat plates thickness etc.

Inside Micrometer

Inside micrometer is used to take direct measurement of internal sizes, such as the diameter of the holes, or the distance between two parallel surfaces.

The principle of measuring it is similar to an outside micrometer.

Measuring by an inside micrometer, its measuring surfaces are hard and grinded in a rounding that allows for accurate measurement and when the instrument needs setting Its movable jaw can be tightened.

Inside Micrometers 25 mm to 50 mm and 50 mm to 150 mm are found to measure in the range, whose reading precision is 0.01 mm.

Depth Micrometer

It is used to measure the depth of holes, slots, projections, recesses, keyways, etc.

Its principle of functioning is similar to that of an outside micrometer.

Its design consists of a grinded and wrapped hard base, which is then recessed with a micrometer head.  

Screw Thread Micrometer 

This micrometer is used to measure the pitch diameter of a screw thread.

Its structure is similar to that of an outside micrometer.

Tube Micrometer 

This micrometer is used to measure the thickness of the walls of tubes, pipes, etc.  Its anvil is spherical.

Rolling Mill Micrometer

This type of micrometer is designed primarily to check the thickness of the seats when rolling, so that the sheet ends are fixed away to measure.

But this micrometer is also used for other measurements where there is a need to take measurements in more depth.  

Electronic Micrometer 

This is a convenient instrument to use.  Measurements with a minimum count of microns (0.001 mm.) are used.

Its spindle opens with the help of a push button and slides on the job.

The size of the measurement is displayed on a dial that can be read easily.

Micrometers of this type are made in different ranges. 

Digital Micrometer

Digital outside micrometer is a modern micrometer used for external dimensions 0.001 mm used to measure in precision.
It has all the parts that are in a Vernier outside micrometer.

Apart from this, it has a digital counter which is fixed on the frame and gives direct numerical reading for quick and accurate measurement. 

Parts of Micrometer 

There are commonly various used micrometer is outside micrometer so here discussed outside micrometers part and also all types of micrometer parts are almost same.

how to read a micrometer
Micrometer Parts

The outside micrometer has the following parts

Frame

It is made from forged steel or malleable cast iron.

With this frame all other parts of micrometers are attached.

Anvil

Anvil about 3 mm is carried out on the frame.

It is one of the measuring ends.
It is made of alloy steel finished in a completely flat surface. 

Spindle 

The spindle moves and grips the job against the anvil.
So that it gets forward and backward movement.

Sleeve

It remains fixed on the frame.
Datum lines and graduation are maintained on it.

It is also known as barrel.
 

Thimble 

It is a tubular cover that is attached to the spindle and moves along the spindle.

There is a bevel edge on the thimble which is divided into 50 equal parts. 
Each 5th is numbered like 0, 5, 10, ... 45

Ratchet Stop 

This is the enlarged section on the thimble. This ensures uniform pressure between the measuring faces.

Spindle Lock Nut 

This is used to lock the spindle in a fixed position. 


Working Principle of Micrometer 

The micrometer works on the screw-nut principle.

During a round, the movement of the length of its spindle is equal to the pitch of the screw.

The movement of the spindle to the distance or part of the pitch can be accurately measured on the sleeve or barrel and the thimble.  

Metric micrometers have 0.5 mm pitch threads on the spindle.
Thus spindle 0.5 mm in one round of Thimble moves forward .

A 25 mm long datum line is formed on the sleeve or barrel.
The entire mm and half mm mark are made on this line.

The circumference of Thimble and bevel edge is divided into 50 equal parts. Therefore, the movement of a division of the thimble is 0.01 mm.
Thus, the Outside Micrometer has an Accuracy or Least Count of 0.01 mm.

How to Read a Micrometer

Finally, now we know step by step how to read a micrometer readings.

Here we will learn to read the metric micrometer. 

Measuring Technique 

There are following technique take to apply during reading a micrometer

1. Clean the face of a measuring micrometer with a soft cloth or paper.  

2. Check the zero setting of the micrometer.  

3. Hold the micrometer from the frame with the left hand and place the job between the anvil and the spindle.  

4. Rotate the ratchet with the right hand and keep moving it until the sound of slip or rattle. 

5. Ensure that the measuring axis is at right angles to the job axis and passes through the center. 

6. Take Reading.

Micrometer Readings

To take readings from a micrometer, the following three items must be taken into consideration.

•Major divisions (the number of whole mm) 

•Minor divisions 
(number of half mm)

•Thimble divisions (in front of the datum line)  

how to read a micrometer
Micrometer Readings

See in figure Lower line shows the major divisions which represent whole millimetres graduation.

Upper line shows minor division which always represent one-half millimetres graduation.

In front of the datum line shows thimble division.
Which is divided into 50 equal division and  which reading shows in thimble division its  multiply with 0.01 mm. 
After then which reading obtained It will be thimble divisions readings.

During reading the Metric micrometer, First read the major division readings.

Then read minor division reading, if additional line shown in minor division.

After that read thimble division reading and its multiply with 0.01 mm.

After that added these three values and which value obtained is a micrometer reading.

Refer to figure and clearly shown 

Major divisions reading – 38 mm

Minor division readings – 0.5 mm

Thimble division readings – 29  mm
Multiply with 0.01 mm
Then found reading is actual thimble division reading
0.29 mm

After that adding these three values and then which final reading obtained.
It will be a micrometer readings.

Micrometer readings – 38+0.5+0.29 = 38.79 mm

Note: Some micrometer manufacturers can reverse the position of full and half millimeters graduations and but The order in which you read the micrometers remains the same.

Zero Error of a Micrometer 

Keep moving the micrometers until it touches the anvil.

If the zero of the thimble does not correspond to the datum line on the sleeve, then the micrometer is called a zero error.

If the micrometer gives a reading in plus, then it has negative zero error.
This error is subtracted from the actual reading.  

If the micrometer gives a reading in minus then it has positive zero error.
This error is added to the actual reading.  

Methods of Removing Zero Error

There are following methods to given for removing zero error

1. By adjusting the sleeve of the micrometer with the help of spanner available in the micrometer box.

2. By adjusting the nut between the micrometer and thimble.
 
3. In some types of micrometers the anvil is fitted by a screw.  They are can be adjusted by screwing or unscrewing the anvil.

Test Pieces of Micrometer

These are round pieces of alloy steel which are hard and grinded in precision as per the range of micrometers such as 25 mm, 50 mm and so on .

These peace’s are used to check the micrometer and  zero error

The following are the reasons why micrometer readings are wrong.  

•Wrong setting of zero line of Thimble. 
 
• Apply too much or too little pressure on the thimble.  

• Missing work.  

• Screw failure.  

•Micrometer frame twisted.  

•Deteriorating micrometer measuring face. 

Care and Maintenance

• Before taking the measurements, wipe the anvil and work and clean it thoroughly. 

• Do not apply excessive pressure while measuring. Often two clicks  of a ratchet are sufficient. 

• When the micrometer is not being used, do not let its anvil faces in contact.

• Thread should be properly greased or oiled.

•Cotton vest should not be used while cleaning the micrometer.

•Do not place the micrometer on the bed of the machine, it may malfunction there.  

• When the micrometer is not in use, keep it in its box.  

After a few months the micrometers keep checking the accuracy.  


So friends here I discussed how to read a micrometer and also its types, parts and working principle etc.
I hope you all clearly understand.

Thank You.

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