Snap gauge is one of the types of go-nogo gauges.
It is a gauging tool which means it assesses whether part of the cylindrical or non-cylindrical shape meets its dimensional specification without actually providing a measurement of the actual value of the dimension.
The snap gauge is used to measure the outer diameter of the jobs of shapes like spherical-shaped jobs just like ring gauges and thickness gauges.
A Snap gauge is used to measure the outer diameter of a job within specified limits by comparing it with the measurement given in the snap gauge.
It can be used to measure the outer diameter of spherical and cylindrical jobs. It is also used to measure the thickness of the cubical or cuboidal blocks.
It is also called a gap gauge and is used to measure the diameter or thickness of art or material.
The shape of the snap gauge is like the C letter of the English Alphabet.
A snap gauge is a tool for inspection and quality control, it provides a rapid means of determining whether the outside dimensions of the parts are within its closed tolerances.
This gauge provides a quick-go and no-go decision of different shapes and features in machining operation.
Snap can be of different shapes and sizes. They can be of A Type, C Type and U Type.
Gauging is used instead of measuring for the following reasons:-
i) Gauges are less expensive than measuring instruments.
ii) The working speed increases as more parts can be checked in lesser time in gauging than the measuring instruments.
iii) Skilled Labour is not required.
Ring gauges and Thickness gauges have similar applications as that of snap gauges. A snap gauge can be used for measuring cylindrical and non-cylindrical objects while a ring gauge can only be used to measure the diameter of cylindrical parts.
Parts Of Snap Gauge:
1) Metal Frame or Body: Snap gauges consist of a metal frame that is the shape of C or U. The jaw of this frame is a set of two anvils.
Anvils are the jaws of the metal frame. Generally, there are single anvils on each face of the gauge but in some models, there is more than one anvil on each face of the gauge.
The anvils can be of the fixed type or adjustable type according to the type of snap gauge.
When the down screw is tightened, the anvil moves upward. When the screw below the go anvil is tightened the go anvil moves upward and when the screw below the no-go anvil is tightened, the no-go anvil goes upward.
The anvils are set according to the size of the job to be measured. The anvils are set by losing the screw, then the anvils are adjusted and then the anvils are set by tightening the screw and the anvils become fixed.
There are two types of anvils in every snap gauge:-
I) Go anvil
ii) No-go anvil
The go end will be of low limit and the no-go end will be of high limit.
Different types of anvils are used depending on the size and shape of the object which is to be gauged.
For easy passage of the part to be checked, sometimes the anvils are chamfered.
There is also a backstop on the inner portion of the frame. This backstop is used to locate the part to be checked. The snap gauge is named so because when the part is inserted between the jaws of the gauge, the spring action snaps the part into the position against the backstop.
This gauge is named a snap gauge because when the object to be measured is inserted between the jaws of the gauge, the object gets snapped into position against the backstop due to spring action.
Most of the snap gauges are handheld and a handle is provided for the user to hold the gauge properly.
Some types of snap gauges can be mounted on the tabletop frame or stand and can be used without holding.
Working Of Snap Gauge:
To ensure accurate gauging, anvils should be checked for parallelism and should be inspected regularly to check for wear.
snap gauge has the capability to access both the upper tolerance limit as well as the lower tolerance limit of the dimensional parameter being measured.
In a snap gauge, the jaws or the anvils have two different measurement widths,
The go anvil is set to the high limit of a shaft or part dimension and the no-go anvil is set to the lower limit.
To take measurements of an object, at first, the object is placed into the frame of the tool and checked whether the object passes the go range section.
If the object passes the go range section means that the object’s dimension is within the upper limit of the object’s tolerance.
After the object passes the upper limit of the object’s tolerance then it is evaluated in the no-go section.
If the object doesn’t pass through the no-go anvil, it means that the object’s lower tolerance on its measured dimension is satisfied and the object is accepted.
If the object doesn’t pass the no-go anvil then it is accepted.
If an object doesn’t pass through the go section of the snap gauge, then the exterior diameter or other value falls above the tolerance limit as specified. These objects are rejected as they have excess material and these objects are sent to be reworked.
Objects that pass through the go and the no-go section are also rejected as the exterior diameter or other value falls below the tolerance limit as specified. These objects do not have enough material in place possibly due to excessive removal of material due to machining and these objects are normally scrapped.
snap gauges can be characterized as being of several different types. Broad
Types of snap gauges:
Based On the Number of ends snap gauges are divided into two types:-
1) Single Ended Snap Gauges :
The single-ended snap gauge has only one end and both the anvils, go and no-go anvils are present on that one end.
Image Of Single-Ended Snap Gauge: Same as Fig 1
2) Double-ended Snap Gauges:
The double-ended snap gauge has two ends in the form of anvils. The go anvil is made for the lower limit and the no-go anvil is made for the upper limit.
It is also known as a solid snap gauge.
Based On usage snap gauges are divided into the following types:-
i) Plain Snap Gauges
In the plain snap gauge, the job to measure should pass through the go side of the plain snap gauge and the job should not pass through or should be restricted to passing through the no-go side of the plain snap gauge.
Image Of Plain Snap Gauge: Same as Fig 1
ii) Thread Snap Gauges
Thread snap gauges are used to measure the outer diameter of the threaded jobs.
It has threaded go and no-go anvils. These are not used in plain surface parts.
Thread Snap Gauges are also known as Thread callipers.
Thread snap gauges further have two types:
a) Normal Thread Snap Gauges
b) Roller Thread Snap Gauges
iii) Dial Snap Gauge:
It is also known as a snap indicator gauge. In this type of snap gauge, a display indicator is added to the tool which can be analog or digital.
This indicator indicates the amount of dedication from the nominal value exhibited by the part being gauged.
iv) Adjustable Snap Gauges
Adjustable snap gauges are adjustable according to the maximum and minimum limits of the part to be checked.
In the adjustable snap gauge go and no go are on the same side but have different adjustable anvils.
v) Progressive Snap Gauge:
A progressive snap gauge is also known as a caliper snap gauge. This type of snap gauge is commonly used for checking large diameters up to 100 mm.
This type of gauge is made of a horseshoe magnet-shaped frame with an I section on it to reduce the weight of the snap gauge.
vi) Position Snap Gauge:-
A position snap gauge is used for checking the position of features in relation to another surface.
vii) Combined Limit Snap Gauge:
This snap gauge is of a double-ended type. The go and no-go dimension is marked in a single gauge and a spherical projection is provided.
The handle is parallel to axes while using the go gauge and the handle is normal to axes while using the no-go gauge.
A slip gauge is also used for the measurement using a snap gauge.
Specifications of snap gauges:
1) Anvil width or thickness:
It shows the width of the anvils i.e the contact area for the measurement surface that will rest against the object.
2) Measurement Range:
It represents the minimum and maximum values of the dimensions that the snap gauge can be used. ie difference between the values measured by go and no-go anvils.
The smaller the measuring range is the higher is the performance of the snap gauge.
Advantages of snap gauges:
1) Measurement can be done using snap gauges at a fast rate.
2) Less dependent on the skill level of the tool user.
3) Snap gauges are less expensive than other measuring instruments.
Disadvantages of Snap Gauge:
1) Snap gauges have limited measurement ranges and cannot be used to measure parts that are beyond their measurement range
2) It is very time-consuming for very large-scale measurements.
3) it cannot be used to measure soft materials.
Precautions for Using Snap Gauges:
1) Anvils should be checked periodically for parallelism for accurate gaging.
2) Any wear of anvils should also be checked periodically.