Hello mechons, welcome to MechGeni, now in this article we are going to explain you about the measuring device named Dial Indicators.
Here now we are going to explain about what are Dial indicators, principle of dial indicator, working of dial indicators, types of dial indicators and also the advantages, disadvantages and applications of dial indicators.
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First lets start with
What are Dial indicators?
A dial indicator is a very important compensator used in mechanical measurement applications.
Principle of Dial indicators
The dial indicator operates on the principle that a very slight upward pressure on the spindle or plunger at the contact point was multiplied through a system of gears and levers and it was indicated on the face of the dial by the pointer of the dial indicator.
The body of the dial indicator contains a round graduated scale and a contact point which is connected with the gear train. So that the pointer on the dial face magnifies and indicates the amount of plunger movement in the dial.
Construction of the dial indicator
The dial gauge consists of the following parts.
- Circular dial body
- Pointer or indicating hand
- Graduated scale
- Revolution counter
- Bezel
- Bezel clamp
- Dust cap
- Stem
- Plunger
which is divided into
- Spindle
- Contact point
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| Parts of a Dial Indicator |
In the side view we can see other Parts
- Crystal
- Back
- Mounting lug
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| Side view of dial indicator |
After opening the body of dial indicator, we can see internal parts and those are
- Rack
- Rack guide
- Gear train
- Hairspring
- coil spring.
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| Working parts of the dial indicator |
Working of dial indicator
Before we see the working of the dial indicator we must first understand how the magnification process is achieved with the help of Gears.
Let us Consider two gears A and B. These gears are meshing with each other. The number of teeths on gear A is less when compared to gear B. The smaller gear A is called Pinion, when we rotate the pinion by one revolution the gear B will rotate through a small angle. This change in angle of rotation on gear B depends on the gear ratio, now suppose if we rotated gear B by one full revolution then the number of revolution of pinion(Gear A) is more.
With this basic concept of the relation of gears now we can see how the magnification of the plunger is achieved in a dial indicator gauge.
The gear and pinion arrangement is used in this instrument to obtain the required high magnification ratio by arranging the gear train in a similar way to that of a clockwise movement.
A perfect sliding plunger is fitted in its own bearings. This plunger carries a rack, which was accurately meshed with pinion A, the rotation of the plunger about its own axis is prevented by a pin attached to it, which is located in a slot in Rack guide
In order to keep the plunger in an extended or normal position the light coil spring is employed. Now the small movement in the contact point causes the rack to rotate the pinion A with which it is being meshed.
The larger gear B is attached to the same spindle as pinion A. The gear B is further meshed with pinion C, which thus magnifies the movement of pinion A attached to the second pinion C.
Now the Gear D which is meshed with the third pinion E mounted on the same spindle.
This magnification is further enlarged at the tip of pointer by an amount depending upon its length
In order to take a backlash a light hair springage is always fitted to the dial gauge gear trains by meshing a gear F to pinion A and attaching spring with gear F is also to prevent gear backlash.
The gears which are used here are Precision cut. And the movement assembly resembles like a high-quality watch.
After final assembly each dial indicator gauge is thoroughly tested, checked and properly calibrated with the help of micrometer head or with the help of slip gauges.
If the pointer moves more than one revolution a revolution counter is also incorporated, which will correctly indicate the number of revolutions made by the main pointer and thus it enables a complete reading to be made when the gauge is used for direct measurement.
We can also rotate the round graduated scale to set the pointer to zero and in some dial indicators the bezel has two range pointers which are used to set the ranges.
( PleaseWatch the video for clear cut understanding )
Applications of dial indicator
- Comparing two Heights or distance between narrow limits
- Determining the errors in the geometrical forms such as ovality roundness and taper
- For taking accurate measurements of deformation such in tension and compression
- Positional errors of surfaces such as parallelism squareness and alignment are being determined with the help of dial indicators.
- Alignment of Lathe centers is being checked with the dial gauge indicators.
- To check the trueness of milling machine Arbors and to check the parallelism of shape or armed with table surface or vice.
Advantages of Dial Indicators
- These are the most perfect tool for taking linear measurements
- It is also used to measure several other measurements by combining with some other attachments to the dial gauge indicator.
- Small in size and can be used in many production units.
- The tool is very efficient to assume the quality of a workpiece
Disadvantages of dial gauge Indicator
- Due to the vibrations of machines the Precision of this instrument is often poor.
- Parallax Effect is also a main disadvantage while taking the measurements