In this article we are going to discuss about the types of gauges in metrology, their uses along with their images. Let’s start with the Definition of Gauge.
What are Gauges ?
Gauges are the mechanical tools that are used by engineers to get certain dimensional information like measuring the tolerance limit of a component, inline with a specified standard. Gauges do not provide the exact dimensional value. They are used to determine whether the measured dimension falls within the specified limit or not.
Gauges can be mechanical or electro mechanical and the readings can be direct reading from the tool or from a digital screen. Now let us have a brief overview of different types of gauges in mechanical engineering.
Types of Gauges in Metrology
Different types of gauges used in every industry are following :-
- Plug plain Gauge
- Snap types
- Ring types
- Pin gauges
- Caliper Gauges
- Feeler gauge
- Screw pitch gauge
- Radius and Fillet Gauges
- Plate gauge and wire gauge
- Indicating gauges
- Air Gauges
- Taper gauges
- Thread gauges
1. Plain Plug Gauge
Plain plug gauges are cylindrical types of gauges which are used for checking holes of many different shapes and sizes. They are used to check the inside diameter limit on manufactured parts. There are plug gauges for straight cylindrical holes, tapered, threaded square and splined holes.
These plain plug gauges are made of proper wear-resistant steel, and the handles are made of any suitable steel, such as light metal handles for heavy plain plug gauges or suitable non-metallic handles for smaller plain plug gauges.
The gauging surface of plain plug gauges is hardened to at least 750 H.V. and is suitably stabilized, ground, and lapped.
Plain plug gauges are double-ended for sizes up to 63 mm and single-ended for sizes greater than 63 mm.
The plain plug gauges are designated by ‘GO’ and ‘NOGO’ as applicable.
Types of Plain Plug Gauges
1. GO and NOGO plain plug gauges for sizes up to 10 mm.
2. GO and NOGO plain plug gauges for size over 10 mm and up to 30 mm (Taper Inserted Type)
3. GO and NOGO plain plug gauges for sizes over 30 mm and up to 63 mm of fastened type.
4. Go and NOGO plain plug gauges for sizes over 63 mm and up to 100 mm of fastened type.
5. GO and NOGO plain plug gauges for sizes over 100 mm and up to 250 mm of flat type. This is a shell form plug gauge. Each plug is relieved to reduced weight.
Figure shows a standard plug gauge used to test the nominal size of a cylindrical hole.
Figure shoes a double ended limit plug gauge used to test the limits of size. At one end it has a plug of minimum limit size the “go” end and ; at the other end a plug of maximum limit, the “no go” end. These ends are detachable from the handle so that they may be renewed seperately when worn.
In a progressive limit plug gauge fig the “go” and “no go” sections of the gauge are on the same end of the handle.
Larger holes are gauged with annular plug gauges, which are shell-constructed for light weight, and flat plug gauges, made in the form of diametrical sections of cylinders.
2. Snap Gauges
Snap gauges are the types of gauges that are used for checking external dimensions. Shafts are mainly checked by snap gauges. They may be solid and progressive or adjustable or double ended. The most usual types illustrated in figure are as follows :
- Solid or non-adjustable caliper or snap gauge with “go” and “no go” ends is used for large sizes.
- Adjustable caliper or snap gauge is used for larger sizes.
- Double ended solid snap gauge with “go” and “no go” ends is used for smaller sizes.
This is made with two fixed anvils and two adjustable anvils, one for the “go ” and the other for the “no go”. The housing of these gauges has two reassess to receive the measuring anvils secured with two screws. The anvils are set for a specified size within an available range of adjustment of 3 to 8 mm. The adjustable gauges can be used for measuring series of shafts of different sizes provided the diameters are within the available range of the gauge.
3. Ring Gauges
Ring gauges are used to test the external diameters. They allow shafts to be checked more accurately since they embrace the whole of their surface. Ring gauges, however, are expensive to manufacture and therefore find limited use. Moreover, ring gauges are are not suitable for measuring journals in the middle sections of shafts.
A common type standard ring gauge shown in the figure. In a limit ring gauge, the “go” and “no go” ends are identified by an annular groove on the periphery. Above about 35mm all gauges are flanged to reduce weight and facilitate handling.
4. Pin Gauges
When the holes to be checked are larger than 75 mm, such as an automobile cylinder, a pin gauge, as shown in the figure, can be used. Pin gauges are such types of gauges.
The gauge is placed lengthwise in the cylinder bore during the measurement, and the measurement is completed. These gauges are particularly useful for measuring grooves or slots.
What do pin gauges measure ?
The PIN GAUGE is the pin shape according to fixed size precisely. The primary purpose of PIN GAUGE is to measure and inspect the diameter of samll holes, it also can be used as a test bar for geometric deviations measurements.
5. Caliper Gauges
A caliper gauge is similar to a snap gauge, but it is used to check the product’s inside and outside dimensions. The inside dimensions (hole diameter) are checked at one end of the caliper gauge, while the outside dimensions are measured at the other (shaft diameter).
6. Feeler Gauges
Feeler gauges are types of gauges used for checking clearances between mating services. They are made in the form of a set of Steel, precision machined blade 0.03 to 1.0 mm thick and 100 mm long. The blades are provided in a holder as shown in the figure. Each blade has indication of its thickness.
The Indian standard establishes 7 sets of feeler gauges : numbers 1, 2, 3, 4, 5, 6, 7, which differ by the number of blades in them and wider range of thickness. Thin blades differ in thickness by 0.01 mm in the 0.03 to 1mm set, and by 0.05 mm in 0.1 to 1.0 mm set.
To find the size of the clearance, one or two blades are inserted and tried for a fit between the contacting surface until blades of suitable thickness are found.
7. Screw Pitch Gauges
Screw pitch gauge serves as an everyday tool used in picking out a required screw and for checking the pitch of a screw threads. They consist of a number of flat blades which are cut out to a given pitch and pivoted in a holder As given in the figure. Each blade is a stamped with the pitch or number of threads per inch and the holder bears and identifying number designating the thread it is intended for. The sets are made for metric threads with an angle of 60 degree, for English threads with angle of 55 degree.
A set for measuring metric threads with 20 blades has pitches form 0.4 to 6 mm and for English threads with 16 blades has 4 to 28 threads per inch.
In checking a thread for its pitch the closest corresponding gauge blade is selected and applied upon the thread to be tested. Several blades may have to be tried until the correct is found.
8. Radius and Fillet Gauges
The functions of these types of gauges is to check the radii of curvature of convex and concave surfaces over a range from 1 to 25 mm. The gauges are made in sets of thin plates curved to different radii at the ends as shown in the figure. Each set consists of 16 convex and 16 concave blades.
9. Plate Gauge and Wire Gauge
The thickness of sheet metal is checked by means of plate gauges, and wire diameters by means of wire gauges. The plate gauge shown in the figure is used to check the thickness of plates from 0.24 to 5.0 mm, and the wire gauge in the figure from 0.1 to 10 mm.
10. Indicating Gauges
Indicating gauges are the types of gauges which employ a means to magnify how much a dimension deviates, plus or minus from a given a standard to which the gauge has been set. They are intended for measuring errors in geometrical form and size, and for testing service for their true position with respect to one another. Besides this indicating gauges can be adapted for checking the run out of two toothed wheels, pulleys, spindles and various other revolving parts of machines.
Indicating gauges can be of a dial or lever type, the former being the most widely used.
11. Air Gauges
Pneumatic or air Gauges are used primarily to determine the inside characteristics of a hole by means of compressed air. There are two types of air Gauges according to operation : a flow- type and a pressure- type gauge
The flow- type operates on the principle of varying air velocities at constant pressure, and the Pressure type operates on the principle of air escaping through an orifice.
Figure illustrates the principle of flow- type gauge which is more widely used at present. Compressed air cleaned and dried through a filter passes through a vertical tapered glass tube containing an indicator float at constant pressure.
The air then passes out through a flexible hose into a gauging head where it escapes through one or more orifices. The amount of flow is controlled by the size of the space between the gauging head and the work and different rates of flow of air in the glass tube covers the indicator float to assume different vertical positions. This is registered in a dial which is calibrated in a fractions of millimetre.
12. Taper Gauges
The most satisfactory method of testing a taper is to use taper gauges. They are also used to get the diameter of taper at some point. Taper gauges are made in both the plug and ring styles and in general, follow the same standard construction as plug and ring gauge. A taper plug and ring gauge is shown in the figure.
When checking a taper hole, the taper plug gauge is inserted into the hole and a slight pressure is exerted against it. If it does not rock in the hole, it indicates that the taper angle is correct. The same procedure is followed in a ring gauge for testing tapered spindle.
The taper diameter is tested for size by noting how far the gauge enters the tapered hole or the tapered spindle enters the gauge. A mark on the gauge shows the correct diameter for the large end of the taper.
To test the correctness of the taper two or three chalk or pencil lines are drawn on the gauge about equidistant along the length or in the hole along a generatrix of the cone. Then the gauge is inserted into the hole and slightly turned. If the lines do not rub off evenly, the taper is incorrect and the setting in the machine must be adjusted until the lines are rubbed equally all along its length. Instead of making lines on the gauge, a thin coat of paint ( red lead, carbon black, Prussian blus, etc. ) Can be applied.
The accuracy of a taper hole is tested by a taper hol is tested by a taper limit gauge illustrated in the figure. This has two check lines “go” and “no go” each at a certain distance from the end face. The “go” portion corresponds to the minimum and the “no go” to the maximum dimension.
13. Thread Gauges
Thread (pitch diameter of thread ) are checked with threads gauges. For checking internal threads (nuts, bushes, etc. ) Plug thread gauges are used, while for checking external threads (screws, bolts ) ring thread gauges or snap gauges are used. Single- piece thread gauges serve for measuring small diameter. For large diameters the gauges are made with removable plug machined with a tang. Standard gauges are made single- piece.
Common types of thread gauges are illustrated in the figure :
Standard plug gauges : It may be made of various kinds
- Plug gauge with only threaded portion
- Threaded portion on on one end and plane cylindrical plug on the opposite end to give correct “core” diameter
- Thread gauge with core and full diameters.
Limit plug gauges : It have a long thread section on the “go” end and a short- thread section on the “no go” end to correspond to the minimum and maximum limits respectively.
Roller ring gauges : Similarly have “go” and “no go” ends. They also be solid and adjustable
Roller snap gauges : Roller snap gauges are often used in production practice for measuring external threads. They comprise a body, two paired “go” rollers and two paired “no go” rollers.
Taper thread gauges : Are used for checking taper threads. The ring thread gauges (taper) are made in two varieties – rigid (non adjustable ) and adjustable. The “go” non-adjustable ring gauges are full threaded while the “no go” have truncated thread profile.
14. Form gauges
Form gauges may be used to check the contour of a profile of a workpiece for conformance to certain shape or form specifications.
Form gauges that are made from sheet steel are called profile or template gauge. A profile gauges may contain two outlines that represent the limits within which a profile must lie as shown in the figure.
These were all the types of Gauges. Hope you loved this article. Please leave a comment about your experience reading this post about the Types of gauges.
Frequently Asked Questions
What are the types of gauges?
The different types of gauges are : Plug plain Gauge, Snap types, Ring types, Pin gauges, Caliper Gauges, Feeler gauge, Screw pitch gauge, Radius and Fillet Gauges, Plate gauge and wire gauge, Indicating gauges, Air Gauges, Taper gauges, Thread gauges,
What are gauges used for?
Gauges are the mechanical tools that are used by engineers to get certain dimensional information like measuring the tolerance limit of a component, inline with a specified standard.
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