Dial Gauge – Parts, Internal Arrangement, Internal Parts Working, Applications, Advantages, and Disadvantages

Dial Gauge is used to measure the flatness and inclination of objects.
It is used to check the roundness of the round bar.
It checks the flatness of an object in comparison to the flatness of the standard object. In the mechanical field, the dial gauge is used to check the flatness and alignment of different jobs and workpieces.
It is very easy to use as compared to other instruments like vernier caliper, micrometer, etc.
This dial gauge is based on the principle of “Rack and Pinion”.
Dial Gauge can measure up to a minimum value of 0.01 mm reading. Hence its least count is 0.01 mm.


Dial Gauge
Dial Gauge

Parts of Dial Gauge Indicator:

1 Case:
There is a metallic casing which is the outermost part of the dial gauge.

2 Graduated Scale:
Inside the casing, a graduated scale is present in which different readings are marked.

3 Pointer:
A pointer is present which points at the measured value on the graduated scale.

4 Small Dial Gauge:
This small dial gauge is present inside the dial gauge. It also has a graduated scale that has reading. This small dial gauge has reverse readings. The reading of the small dial gauge can be straight or reverse based on the mechanism used in the gear train for the movement of the pointer in the small dial gauge.

5 Small dial pointer:
There is a small pointer that points at the measured value in the graduated scale of the small dial indicator. It is also called short hand indicator.

6 Stem:
The plunger or spindle moves up and down inside this stem.

7 Contact Point:
This contact point will have contact with the surface and will help in the movement of the plunger.

When the pointer of the outer indicator will complete its revolution, then the pointer of the small indicator will move from 0 to 1 i.e small dial indicator will show 1 mm when it big indicator will cross 100 reading in the big dial indicator.
When the outer pointer will complete its 10 rotations then the pointer of the small indicator will return to zero.
The small dial gauge is very helpful in taking a reading.

The internal arrangement of dial gauge:

In the internal part of the dial gauge, there is a rod and in this rod, there are racks cut on this rod.
This rack is connected to a small gear S1 and this small gear S1 is attached to the big gear G0 and both have the same axis.
This small pinion is also connected to another big gear G1. If the small gear S1 takes 10 rotations, then the big gear G1 which is connected to the small gear S1 will complete 1 rotation in the opposite direction.

Now, this big gear G1 is also connected to another small gear S2 which is the gear of the outer dial pointer and this small gear S2 is attached to a big gear G2 and both have the same axis. This big gear G2 is connected to a helical spring.
The main function of the helical spring is that it stores the rotational energy of the gears when the gears rotate.
This helical spring is used to reset the positions of the gear and the pointers. When the measurement is completed, the helical spring transfers the stored energy to the connected gear and all the gears move in the reverse direction one by one and reach their initial position. Also, the rod moves to its initial position.

Working of internal parts:

When the dial gauge is put over a workpiece, the rod of the dial gauge moves upward and the racks which are cut on it also moves.
The small gear S1 which is connected to the rack on the rod starts rotating. When the rod will move upward the small gear will rotate in the clockwise direction.
This small gear S1 is connected to a big gear G1. This big gear G1 controls the pointer P2 which is the pointer of the small dial gauge. When the small gear S1 rotates in clockwise then the big gear G1 will rotate in an anti-clockwise direction and the pointer P2 attached to the big gear G1 will also rotate in an anti-clockwise direction.
As this big gear G1


will rotate in an anti-clockwise direction, then the small gear S2 of the outer dial will rotate in the clockwise direction and hence the pointer of the outer dial P1 will rotate in the clockwise direction. Also, the big gear G2 will also rotate in a clockwise reaction.
Now this big gear G2 is connected to the helical spring and the helical spring will rotate in an anti-clockwise direction and will store the rotational energy and when the work will be completed then the helical spring will give its energy back to the gears and the gears and the pointers will move back to their initial positions. As all the gears will move in the opposite direction. So the rod with racks will also move upward and will move back to its initial position.

Least count of Dial Gauge Indicator:

100 lines reading in outer scale = 1mm = 1 full rotation on outer scale

Therefore, least count = 1 rotation on the main scale / No of division moved on the dial scale.

1 Rotation On Main Scale = 1mm
No. of division moved on dial scale = 100

Hence, Least Count = 1mm /100 = 0.01mm.

How to take a reading on Dial Gauge:

Let us assume that we use a dial gauge to measure the flatness of a workpiece.
When we use the dial gauge to measure the flatness of the workpiece, it shows some variation.
Let the small dial gauge shows a reading of a little more than three (3).

First, we will note the reading of the small dial indicator. We will take the only complete reading of the small indicator. so, if the reading is a little more than three then we will only take reading three and neglect the rest.
When the big dial pointer will complete one full rotation the small dial pointer will move one unit which is equal to 1mm. After taking the reading of the small dial indicator, a reading of the outer dial is taken. Let the reading of the outer dial indicator is 42.
After taking a reading of both the indicator we calculate the variation in mm using this formula:
Formula for variation ( in mm ) = Short dial reading + ( outer dial reading x least count )
Now taking the assumed values we have,
Variation = 3 + ( 42 x 0.01 )
= 3.42 mm

This 3.42 mm is the exact reading of variation in the surface using the dial gauge indicator.

Types Of Dial Gauge:

There are mainly two types of dial gauge:
1) Plunger Dial Gauge
2) Liver Dial Gauge

Also, dial gauges of different least counts are available:
1) 1 Micron or 0.001 mm
2) 2 Micron or 0.002 mm
3) 10 Micron or 0.01 mm
The last one of 10 Micron or 0.01 mm is the most used dial gauge. Others are also used but very rarely.

Applications of Dial Gauge:

1) Comparing two heights or distances.
2) It is used to measure the deformation such as in tension or compression.
3) To check the errors in geometrical form such as ovality, roundness, run out, and taper.
4) It is used to measure pit depth in EDM ( Electric Discharge Machine )
5) It is used to measure surface roughness.
6) It is used to determine the potential errors of surfaces such as parallelism and alignment.
7) Used to align job in lathe centers.
8) It is used to check the trueness of the milling machine.
9) It is used to inspect the precision of the workpiece in a grinding machine.

Advantages Of Dial Gauge:

1) Size of the dial gauge is very small and compact, so it can be used easily in mass production.
2) Dial gauges can be used to measure the amount of tapper in round objects easily.
3) It is the most flawless tool in taking linear measurements.

Disadvantages of Dial Gauge:

1) The precision of the dial gauge is often lost due to the vibration of machinery.
2) The main disadvantage of the dial gauge is parallax error.
Parallax error: Parallax error occurs when the measurement of an object’s length is more or less than the true length because of your eye being positioned at an angle to the measurement markings. )
3) Due to space constraints the tool is needed to be installed at an angle due to which the accuracy of the device is lost.

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