Comparators are the devices which are used to find only dimensional difference between the actual manufactured component and standard or master component.
Sine bar
Wednesday, 13 April 2016
Sine bar is an instrument which is used for measuring smaller taper angles. Here taper means slant(inclined). So, the smaller angles are determined accurately by using Sine bar.
While using a Sine bar for finding the taper angles, some other intermediate equipment are required. Those are Surface plate, Slip gauges and a Dial indicator. By using all these tools a proper arrangement is made to find the taper angle value.
Methodology:
First we should clean the surface plate by using oil or grease to remove dust particles on the plate. Now, take the Sine bare and clean it too and place it on the surface plate. The cleaning of the tools is very important to confirm the accuracy in the measurement. Take the tapered object whose angle is to be measured and place it on the sine bar. Now, take the dial indicator and place it on the surface plate. Arrange the plunger of the dial indicator on the taper object where the smallest height of the taper surface takes place. While arranging the plunger at this end, apply some initial pressure to the plunger. After that make the indicator on the dial pad to coincide with zero by rotating the bezel of the dial indicator. When you rotate the bezel, the dial pad also rotates. Now move the indicator on the taper object from initial end to final end and observe the reading on the dial indicator. This reading gives you the height of the slant of the tapered surface. What ever the value we get on the dial indicator according to that we need to select the number of slip gauges to that value. The thickness of the slip guage would be given its surface. By observing its thickness select the slip guages by joining which we get the same value as we observed on the dial indicator.
Now, take those slip gauges and arrange them below one of the rollers of the sine bar where the smallest height of the taper object is taking place. When you do this the taper surface of the object becomes parallel to the surface plat. To confirm the accuracy of the parallelism once again move the dial indicator over the tapered surface. If any fluctuations are there in dial indicator in clockwise or anti clockwise, we should add or remove the gauges for confirming the parallelism of the taper surface with the surface. Once there is no fluctuation the dial indicator while moving over the taper surface from one end to another end, then we can confirm the parallalism. The total arrangement is given in the figure below provided.
Now, we need to apply the sine rule by constructing a right angle triangle with the help of height of the slip gauges and distance between the rollers of the sine bar as shown in figure below. Then we can find the what is the theta value which is only the required value.
The distance between the rollers is in between a range of 100 mm to 150 mm.
While using a Sine bar for finding the taper angles, some other intermediate equipment are required. Those are Surface plate, Slip gauges and a Dial indicator. By using all these tools a proper arrangement is made to find the taper angle value.
Methodology:
First we should clean the surface plate by using oil or grease to remove dust particles on the plate. Now, take the Sine bare and clean it too and place it on the surface plate. The cleaning of the tools is very important to confirm the accuracy in the measurement. Take the tapered object whose angle is to be measured and place it on the sine bar. Now, take the dial indicator and place it on the surface plate. Arrange the plunger of the dial indicator on the taper object where the smallest height of the taper surface takes place. While arranging the plunger at this end, apply some initial pressure to the plunger. After that make the indicator on the dial pad to coincide with zero by rotating the bezel of the dial indicator. When you rotate the bezel, the dial pad also rotates. Now move the indicator on the taper object from initial end to final end and observe the reading on the dial indicator. This reading gives you the height of the slant of the tapered surface. What ever the value we get on the dial indicator according to that we need to select the number of slip gauges to that value. The thickness of the slip guage would be given its surface. By observing its thickness select the slip guages by joining which we get the same value as we observed on the dial indicator.
Dial Indicator
Slip gauges box
Now, take those slip gauges and arrange them below one of the rollers of the sine bar where the smallest height of the taper object is taking place. When you do this the taper surface of the object becomes parallel to the surface plat. To confirm the accuracy of the parallelism once again move the dial indicator over the tapered surface. If any fluctuations are there in dial indicator in clockwise or anti clockwise, we should add or remove the gauges for confirming the parallelism of the taper surface with the surface. Once there is no fluctuation the dial indicator while moving over the taper surface from one end to another end, then we can confirm the parallalism. The total arrangement is given in the figure below provided.
Now, we need to apply the sine rule by constructing a right angle triangle with the help of height of the slip gauges and distance between the rollers of the sine bar as shown in figure below. Then we can find the what is the theta value which is only the required value.
surface integrity
Monday, 27 October 2014
Surface integrity means it is a condition of surface of a component after manufacturing process. After manufacturing process the surface may be consisting of smoother surface or surface with irregularities. These conditions depends on the process characteristics of manufacturing process we have selected for the component.
Generally, a component is made by casting operation or any other machining operations. By taking care of the process characteristics for these two processes we can get the desired surface finishing for the component. For the casting operation what are the process characteristics means preparation of proper mould cavity with high compact strength, passage ways with smoother surface inside, proper cross sectional areas for the passage ways which provides uniform flow of the molten form of metal, getting totally converted form of metal etc. For machining operation process characteristics are constant speed ratio between worpiece and tool, uniform feed rate and proper depth of cut etc. So, maintaining all these process characteristics in optimum condition we can avoid the irregularities may take place on the surface of component.
Surface integrity is considered in two forms based on the irregularities and reasons for getting irregularities on the surface of a component after manufacturing process. Those two forms are Topography characteristics and surface layer characteristics. The topography characteristics are related to the irregularities related to roughness, waviness, flaws and lays. Surface layer characteristics are those irregularities which are due to the high heat applied to component which causes the change in crystal structure, grain structure and ultimately causes the variation of properties of metal of component.
Measurment of Pitch:
Monday, 13 October 2014
A pitch value a screw thread can be measured in so many ways like by using screw pitch gauges, screw plug gauges and also by Tool Maker's Microscope. The screw pitch gauges are provided in a form of number of blades. Each blade provided with different thread profiles having different pitch values. The pitch value of each thread profile is mentioned on the blade. After manufacturing desired threads, the pitch value is checked by matching the profile with the number of pitch gauges.
Screw pitch gauges
A pitch value of external threads can also be determined by using Tool Maker's Microscope. In this method the pitch value can be measured by using two micrometers provided in longitudinal and traverse direction. By using the same cross mark, we should place the cross mark on any crest point or root point and then we should move that cross mark to the successive crest or root point by using the longitudinal micrometer. In between these two positions we should take micrometer readings as initial and final reading. The difference between these two readings is the desired pitch value.
Using a Pitch measuring machine:
A pitch measuring machine consists of two vertical slides provided with two screws. These two screws are provided for fixing a threaded component. It means we have to adjust the component in between the two screws of slides. These slides be sliding on the guide of base of this machine. This machine is also consisting of an indicator provided with stylus. According to the movement of the stylus the reading on the indicator will be changing. This indicator is provided on a guide way which will be sliding in traversing direction. Here one of the sliding is provided with a micrometer head.
After adjusting the threaded component in between the screws, we should insert the stylus of indicator in the thread and we should make the reading on indicator as zero. Then we should rotate micrometer so that the thread component moves in longitudinal direction. So, the reading on indicator changes. We should move the component until the reading again becomes zero. It means the stylus moved from a point on a flank surface to the next successive point on the next flank surface. Here, in between these two positions we should take two micrometer readings. The difference between two micrometer readings is the desired pitch value.
A pitch measuring machine consists of two vertical slides provided with two screws. These two screws are provided for fixing a threaded component. It means we have to adjust the component in between the two screws of slides. These slides be sliding on the guide of base of this machine. This machine is also consisting of an indicator provided with stylus. According to the movement of the stylus the reading on the indicator will be changing. This indicator is provided on a guide way which will be sliding in traversing direction. Here one of the sliding is provided with a micrometer head.
After adjusting the threaded component in between the screws, we should insert the stylus of indicator in the thread and we should make the reading on indicator as zero. Then we should rotate micrometer so that the thread component moves in longitudinal direction. So, the reading on indicator changes. We should move the component until the reading again becomes zero. It means the stylus moved from a point on a flank surface to the next successive point on the next flank surface. Here, in between these two positions we should take two micrometer readings. The difference between two micrometer readings is the desired pitch value.
Measurement of Thread angle:
Monday, 13 October 2014
A Thread angle of a given screw thread can be determined by using Tool Maker's microscope. The microscope gives an enlarged view of the thread profile. In Tool Maker's microscope an illuminating unit is provided below a measuring table. This illuminating unit will focus the edge profile or contour shape of the thread. By getting the contour shape we can find the thread angle.
The Tool Maker's microscope is provided with a cross mark(x) on its primary eye piece. In this cross line, we have to adjust one line to one flank surface as it is aligning to it. In this position we should take the protractor disc reading as initial reading. Then after we should rotate the protractor as the same line of cross mark aligns with the opposite flank surface. In this second position again we should take the protractor reading as final reading. The difference between the two readings will be the desired angle value.
The Tool Maker's microscope is provided with a cross mark(x) on its primary eye piece. In this cross line, we have to adjust one line to one flank surface as it is aligning to it. In this position we should take the protractor disc reading as initial reading. Then after we should rotate the protractor as the same line of cross mark aligns with the opposite flank surface. In this second position again we should take the protractor reading as final reading. The difference between the two readings will be the desired angle value.
Tool Maker's Microscope
Measurement of Minor diameter of External and Internal Threaded component
Sunday, 12 October 2014
Minor Diameter of External Threaded component:
The minor diameter of external threads can be determined by using a special type of micrometer which is provided with number of V-peices. These V pieces are changeable according to the root diameter of the thread profile. This method is used for British standard and British association threads. While measuring the minor diameter, the V pieces are connected to micrometer anvil and the screw is adjusted in between the anvils as tip diameter of V pieces matches with the root diameter of thread profile. If it is not exactly matching we should change the V pieces until a perfect match is obtained. Once the perfect match is obtained, then we should take the reading on micrometer which gives the minor diameter of screw or external threaded component.
Measurement of Minor Diameter of Internal Threaded component(Nut):
Minor diameter of an internal threaded component can be measured by two methods as they are by using Tapered Parallels and using Rollers & Slip gauges.
In the method of using tapered parallels, the tapered plates are placed at initial position on each other as they give minimum height and then they are inserted into a nut component. After inserting in a nut, they are slide on each other as the height be increasing. The sliding of tapered parallels is done until their top and bottom surfaces touch the crest points of the internal threads. Once they touch there will be no movement and in this position we should find the height of the plates by using micrometer. The micrometer anvils are to be arranged on the plates and reading should be taken.This reading will give the minor diameter of the Internal threaded component(nut).
In the method of using rollers and slip gauges, the two rollers are adjusted inside a nut with the help of slip gauages. It means in between the rollers number of slip guages are arranged as per gap taking place between the rollers. Here the diameter of rollers and width of slip gauages are known. By adding all these values we can find the minor diameter of an internal threaded component or a nut.
The minor diameter of external threads can be determined by using a special type of micrometer which is provided with number of V-peices. These V pieces are changeable according to the root diameter of the thread profile. This method is used for British standard and British association threads. While measuring the minor diameter, the V pieces are connected to micrometer anvil and the screw is adjusted in between the anvils as tip diameter of V pieces matches with the root diameter of thread profile. If it is not exactly matching we should change the V pieces until a perfect match is obtained. Once the perfect match is obtained, then we should take the reading on micrometer which gives the minor diameter of screw or external threaded component.
Measurement of Minor Diameter of Internal Threaded component(Nut):
Minor diameter of an internal threaded component can be measured by two methods as they are by using Tapered Parallels and using Rollers & Slip gauges.
In the method of using tapered parallels, the tapered plates are placed at initial position on each other as they give minimum height and then they are inserted into a nut component. After inserting in a nut, they are slide on each other as the height be increasing. The sliding of tapered parallels is done until their top and bottom surfaces touch the crest points of the internal threads. Once they touch there will be no movement and in this position we should find the height of the plates by using micrometer. The micrometer anvils are to be arranged on the plates and reading should be taken.This reading will give the minor diameter of the Internal threaded component(nut).
In the method of using rollers and slip gauges, the two rollers are adjusted inside a nut with the help of slip gauages. It means in between the rollers number of slip guages are arranged as per gap taking place between the rollers. Here the diameter of rollers and width of slip gauages are known. By adding all these values we can find the minor diameter of an internal threaded component or a nut.
Measurement of major diameter of internal thread
Sunday, 5 October 2014
There is no perfect method for finding the elements of internal threads. But even we can find them by using screw pitch gauages and screw plug gauges. By using pitch gauges we can measure or check pitch value and by using the screw plug gauge we can measure or check major diameter.
Screw pitch gauges
Screw plug
Another approximation method is preparing the cast of the internal thread profile and following the same procedure as for the external threads. For preparing the cast of the internal thread, the nut is fixed in between two wooden blocks with certain gap. Through this gap molten form of metal like wax or sulphur is poured into the nut. Before pouring the molten metal, the internal thread profile should be properly cleaned and brushed from all the dust with oil. The molten metal should be poured upto a level of less than the radius of internal thread for easy removal. After solidification we have to remove the metal by lifting it up and then we should go for the measurements.
Another approximation method is preparing the cast of the internal thread profile and following the same procedure as for the external threads. For preparing the cast of the internal thread, the nut is fixed in between two wooden blocks with certain gap. Through this gap molten form of metal like wax or sulphur is poured into the nut. Before pouring the molten metal, the internal thread profile should be properly cleaned and brushed from all the dust with oil. The molten metal should be poured upto a level of less than the radius of internal thread for easy removal. After solidification we have to remove the metal by lifting it up and then we should go for the measurements.
Measurement of Major diameter of a screw thread
Sunday, 5 October 2014
The major diameter of a screw thread can be determined by a normal micrometer by carefully adjusting the screw in between in two anvils of micrometer. But there is a difficulty of pressure application during adjusting the screw in between the anvils. Due to this pressure the chance of errors in measurement becomes more. So, to avoid this a special instrument that is bench micrometer used.
A bench micrometer consists of two anvils, one is connected to fudicial indicator and another is connected to micrometer head. The fudicial indicator confirms the application of uniform and light pressure while adjusting the screw in between the two anvils. The micrometer gives the desired reading. Generally for finding the major diameter of a screw, a setting cylinder is used which a standard piece equal to the major diameter. It is used to avoid pitch errors in a micrometer screw if any. First, micrometer reading is taken for setting cylinder and the reading is assumed as R1. Next, the micrometer reading is taken for required screw and the reading is assumed as R2. The final measurement is obtained by the following formula without any errors.
Major diameter = D±(R2-R1)
D = Setting cylinder diameter
R1 = Micrometer reading on setting cylinder
R2 = Micrometer reading on screw thread
A bench micrometer consists of two anvils, one is connected to fudicial indicator and another is connected to micrometer head. The fudicial indicator confirms the application of uniform and light pressure while adjusting the screw in between the two anvils. The micrometer gives the desired reading. Generally for finding the major diameter of a screw, a setting cylinder is used which a standard piece equal to the major diameter. It is used to avoid pitch errors in a micrometer screw if any. First, micrometer reading is taken for setting cylinder and the reading is assumed as R1. Next, the micrometer reading is taken for required screw and the reading is assumed as R2. The final measurement is obtained by the following formula without any errors.
Major diameter = D±(R2-R1)
D = Setting cylinder diameter
R1 = Micrometer reading on setting cylinder
R2 = Micrometer reading on screw thread
Effect of pitch error
Saturday, 4 October 2014
The pitch error causes increase in effective diameter of bolt or screw and decrease in effective diameter of nut. If δp is the pitch error then increase in effective diameter of bolt or decrees in effective diameter of nut is given by the relation for whit-worth thread = 1.921xδp.
If δθ1 and δθ2 are errors in flank angles in opposite directions, then increase or decrease in effective diameter of bolt or nut = 0.0105xp(δθ1+δθ2).
We can also say that, the errors in pitch and angle are useful for the alternation of effective diameter. But there is a limit to the errors for accurate work. The maximum limit for the equivalent effective diameter is = 1.921xδp+ 0.0105xp(δθ1+δθ2).
The virtual diameter can be defined as the sum of simple effective diameter and maximum limit for the equivalent effective diameter.
If any difficulty is taking place in an assembly of two bolt and nut with pitch errors in bolt, by increasing the effective diameter of the nut we can assemble the two bolt and nut. In this the pitch error is distributed over the length of engagement.
If δθ1 and δθ2 are errors in flank angles in opposite directions, then increase or decrease in effective diameter of bolt or nut = 0.0105xp(δθ1+δθ2).
We can also say that, the errors in pitch and angle are useful for the alternation of effective diameter. But there is a limit to the errors for accurate work. The maximum limit for the equivalent effective diameter is = 1.921xδp+ 0.0105xp(δθ1+δθ2).
The virtual diameter can be defined as the sum of simple effective diameter and maximum limit for the equivalent effective diameter.
If any difficulty is taking place in an assembly of two bolt and nut with pitch errors in bolt, by increasing the effective diameter of the nut we can assemble the two bolt and nut. In this the pitch error is distributed over the length of engagement.
Errors in Threads
Friday, 3 October 2014
Errors in screw threads are related to the five elements of the screw threads. They are major diameter, minor diameter, pitch diameter, pitch and thread angle. If any errors are taking place in these five elements the produced screw is rejected. So, these elements are also be checked with proper gauging system carefully. The threads are produced by a point cutting tools.
The errors in major and minor diameter cause interference of the mating threads, less root section, less wall thickness and poor contact of the flanks, which ultimately cause the weak in strength of the component. The errors in effective diameter also cause the interference of the flanks.
The errors in pitch and thread angle also cause the progressive tightening of the mating parts due to the interference of the flank surfaces.
Let us discuss some important errors in thread forms. They are
Due to this flank surface will not be as a straight edge, it will be as curved form.
Pitch errors:
The pitch errors are due to improper ratios of cutting tool velocity to rotating velocity of the workpiece. these pitch errors are again classified as
Progressive pitch erros
Periodic pitch errors
Irregular errors
Progressive errors: In this the pitch error results increasing of major or minor diameter or decreasing of major or minor diameter. It means the error may either in increasing order or decreasing order.
Periodic errors: In this the pitch error causes the errors to repeat at certain time of interval.
Irregular errors: These are the errors randomly take place on threads without any specific reason. These are the combination of all the errors take place on threads.
The errors in major and minor diameter cause interference of the mating threads, less root section, less wall thickness and poor contact of the flanks, which ultimately cause the weak in strength of the component. The errors in effective diameter also cause the interference of the flanks.
The errors in pitch and thread angle also cause the progressive tightening of the mating parts due to the interference of the flank surfaces.
Let us discuss some important errors in thread forms. They are
- Drunken error
- Pitch errors
Due to this flank surface will not be as a straight edge, it will be as curved form.
Pitch errors:
The pitch errors are due to improper ratios of cutting tool velocity to rotating velocity of the workpiece. these pitch errors are again classified as
Progressive pitch erros
Periodic pitch errors
Irregular errors
Progressive errors: In this the pitch error results increasing of major or minor diameter or decreasing of major or minor diameter. It means the error may either in increasing order or decreasing order.
Periodic errors: In this the pitch error causes the errors to repeat at certain time of interval.
Irregular errors: These are the errors randomly take place on threads without any specific reason. These are the combination of all the errors take place on threads.
Screw Thread Metrology
Friday, 3 October 2014
A Screw Thread Metrology deals with the measurements of the threads. To understand what are the measurements we can take from screw threads, we should know about the terms or elements of the threads. The Screw Thread Terminology gives the list of the terms and their definition those terms.
Screw Thread Terminology:
The following are the terms of the screw threads:
- Screw thread
- External thread
- Internal thread
- Mulitple start thread
- Axis of thread
- Left hand or Right hand thread
- Form of thread
- Crest of thread]
- Root of thread
- Flanks of thread
- Angle of thread
- Flank angle
- Pitch
- Lead
- Thread per inch
- Lead angle
- Helix angle
- Depth of the thread
- Axial thickness
- Fundamental triangle
- Truncation
- Addendum
- Dedendum
- Major diameter
- Minor diameter
- Effective diameter
The threads formed on cylinder are known as straight threads and the threads formed on a cone or a fulcrum of a cone are known as tapered threads.
External Thread: Threads formed on the outside of the workpiece body are known as external threads.
Ex: Bolts and Studs etc.
Internal Thread: The threads formed on inside of the workpiece body are known as Internal Threads.
Ex: Nuts
Multiple start screw thread: It is a screw which is made by forming two or more than two helical grooves or teeth with equally spaced and similarly formed in an axial section on a cylinder.
Axis of thread: It is an imaginary line which takes place longitudinally through the center of the screw.
Right hand or left hand thread: The Thread is placed in such a way that its logitudinal axis is normal to the observer and the thread is rotated in clockwise direction, if it is moving away from the observer, then it is a right hand thread; if it is moving towards the observer, then it is left hand thread.
Form of thread: It is an edge shape of one complete thread as seen in axial section.
Crest of thread: It is the top most point of the groove forming threads.
Root of thread: It is the bottom point of the groove forming threads.
Flanks of threads: These are the straight edge surfaces which joins the crest to root.
Angle of thread: It is an angle between two opposite flanks or slopes of a thread measured in an axial plane.
Flank angle: It is an angle between individual flanks and a plane perpendicular to the axis of the thread. This angle is similar to the half of the thread angle.
Pitch: It is the distance between the two successive crest points or root points measured parallel to the axis of the thread.
Lead: It is the distance moved by the screw for one complete revolution with respect to its mating part. Some times the lead is equal to the pitch but not always.
Thread per inch: It is the number of threads taking place per one inch. It is reciprocal of the pitch.
Lead angle: It is an angle made by helical curve of the thread at pitch line with a plane perpendicular to the axis of the thread.
Helix angle: It is an angle made by the helical curve of the thread with the axis of the thread.
Depth of thread: It is the distance between crest point and root point which is measured along a plane perpendicular to the axis of thread.
Axial thickness: It is the distance between two opposite faces of the same thread which is measured along the pitch line.
Pitch line is a line which divides a thread profile into two equal parts.
Fundamental triangle: This is made by extending the flanks and joing the points B and C. Thus the triangle ABC is referred to as fundamental triangle. The point A is called as Apex.
Truncation: The truncation at the crest s the radial distance from the crest to the nearest apex of the fundamental triangle. Truncation is given on both sides of a thread profile that is at crest and root.
Addendum: It is the radial distance between crest point and pitch line.
Dedendum: It is the radial distance between root point and pitch line.
Major diameter: It is defined as the diameter of an imaginary cylinder which passes through the crest points of the thread.
Minor diameter: It is defined as the diameter of an imaginary cylinder which passes through the root points of the thread.
Mean or Effective or Pitch diameter: It is defined as the diameter of an imaginary cylinder which passes through the pitch line of the screw threads.
Hole Basis system and Shaft Basis System
Monday, 15 July 2013
Hole Basis system: If the system of assembly of shaft and hole is consisting of basic hole, then that type of system is known as Hole Basis System. It means for the system of assembly of shaft and hole, the zero line will be lying on the minimum diameter of the hole as shown figure. For this system the lower limit size of hole is equal to basic size.
Hole basis system
Shaft Basis system: If the system of assembly of shaft and hole consisting of basic shaft, then that type of system is known as Shaft Basis System. It means for the assembly of shaft and hole, the zero line will be lying on the maximum size of the shaft as shown. For this system the Upper Limit Size of shaft is equal to the Basic Size.
Shaft Basis System
Basic Hole and Basic Shaft
Monday, 15 July 2013
Basic Hole: If the lower limit size or minimum size of hole is equal to the basic size then that type of hole is known as basic hole for a given assembly of hole and shaft.
For the basic hole the zero line will be lying on minimum size of the hole. For the Basic Hole the lower deviation is zero because the difference between the Lower Limit Size and Basic Size is zero.
Basic Shaft: If the upper limit size or maximum size of the shaft is equal to the basic size then that type of hole is known as Basic Shaft for a given shaft and hole assembly.
For the basic shaft the zero line will be lying on the maximum size of the shaft. For the basic shaft upper deviation will be zero because the difference between Upper Limit Size and Basic Size is zero.
For the basic hole the zero line will be lying on minimum size of the hole. For the Basic Hole the lower deviation is zero because the difference between the Lower Limit Size and Basic Size is zero.
Basic Shaft: If the upper limit size or maximum size of the shaft is equal to the basic size then that type of hole is known as Basic Shaft for a given shaft and hole assembly.
For the basic shaft the zero line will be lying on the maximum size of the shaft. For the basic shaft upper deviation will be zero because the difference between Upper Limit Size and Basic Size is zero.
Fits and its typs
Wednesday, 10 July 2013
Fit is defined as a degree of tightness or looseness between two mating parts to perform definite function when they are assembled together.
A fit may result either in a movable joint or a fixed joint. For example, a shaft running in a bearing can move in relation to it and thus forms a movable joint, where as, a pulley mounted on the shaft forms a fixed joint.
Types of Fits:
There are 3 types of fits. They are
i) Clearance fit
ii) Transition fit
iii) Interference fit
Clearance fit: In this type of fit the shaft diameter is always less than the hole diameter. For any given shaft and hole assembly clearance fit can be decided by the statement as according to the limits if the upper limit size of the shaft is less than the lower limit size of the hole then that type of fit is known as clearance fit. So that the shaft can slide or rotate through different degree of freedom according to the purpose of the mating parts.
Maximum clearance: It is the difference between the maximum size of the hole and minimum size of the shaft.
Minimum clearance: It is the difference between the minimum size of the hole and maximum size of the shaft.
Clearance Fit
Interference fit: In this type of fit the minimum diameter of the shaft is always greater than the maximum size of the hole. This type of fit between the shaft and hole will give the permanent type of fit and can be used as a solid component.
Elastic strains developed on the mating surfaces during the process of assembly prevent relative movement of the mating parts.
Interference fit
Transition fit: This type of fit lies mid way between clearance fit and interference fit. In this type size limits on the mating parts so selected may give clearance fit or interference fit depending on the actual sizes of the parts.
Transition Fit
A fit may result either in a movable joint or a fixed joint. For example, a shaft running in a bearing can move in relation to it and thus forms a movable joint, where as, a pulley mounted on the shaft forms a fixed joint.
Types of Fits:
There are 3 types of fits. They are
i) Clearance fit
ii) Transition fit
iii) Interference fit
Clearance fit: In this type of fit the shaft diameter is always less than the hole diameter. For any given shaft and hole assembly clearance fit can be decided by the statement as according to the limits if the upper limit size of the shaft is less than the lower limit size of the hole then that type of fit is known as clearance fit. So that the shaft can slide or rotate through different degree of freedom according to the purpose of the mating parts.
Maximum clearance: It is the difference between the maximum size of the hole and minimum size of the shaft.
Minimum clearance: It is the difference between the minimum size of the hole and maximum size of the shaft.
Interference fit: In this type of fit the minimum diameter of the shaft is always greater than the maximum size of the hole. This type of fit between the shaft and hole will give the permanent type of fit and can be used as a solid component.
Elastic strains developed on the mating surfaces during the process of assembly prevent relative movement of the mating parts.
Transition fit: This type of fit lies mid way between clearance fit and interference fit. In this type size limits on the mating parts so selected may give clearance fit or interference fit depending on the actual sizes of the parts.
Transition Fit
Basic terminology for understanding the limits by conventional diagram
Saturday, 6 July 2013
There are various terms are there to understand the limits given to certain objects. These terms are explained by using simple shaft and hole assembly. The following are the terms related to limits.
Basic size: It is a standard size of hole or shaft which is decided during the designing process with which limits are to be decided.
Actual size: It is a final dimension of hole or shaft which is measured after manufacturing process.
Zero line: It is straight line which is drawn to represent the basic size. All limits and fits are explained with the reference of the zero line.
Tolerance: It is defined as permissible variation that are to be given onto the dimensions of the product.
It can be also defined as difference between the maximum size of the object and minimum size of the object.
Generally the tolerance is given in terms of Upper limit and Lower limit in between which final dimension of the object should be.
Upper limit: It is a limit which is given to the dimension of any object to determine the upper limit size or maximum size of that object.
Lower limit: It is a limit which is given to the dimension of any object to determine the lower limit size or minimum size of that object.
Tolerance zone: It defined as an area formed by the difference between maximum dimension and minimum dimension of the object.
Deviation: It is defined as the algebraic difference between limit of shaft or hole and basic size of the shaft or hole.
There are two types of deviations. They are i) Upper deviation ii) Lower deviaton
Upper deviation: It is defined as the difference between upper limit size and the corresponding basic size. It is represented by ES for hole and es for shaft. It is positive when the upper limit size is greater than the basic size. It is negative when the upper limit size is less than the basic size.
Upper deviation = Upper limit size - Basic size
Lower deviation: It is defIned as the difference between lower limit size and the corresponding basic size. It is represented by EI for hole and ei for shaft. It is positive when the lower limit size is greater than the basic size. It is negative when the lower limit size is less than the basic size.
Lower deviation = Lower limit size - Basic size
The tolerance is also defined in terms of upper deviation and lower deviation. It is given as
For shaft
IT = es - ei ( upper deviation - lower deviation)
For hole
IT = ES - EI
Fundamental deviation: It is a deviation either upper deviation or lower deviation which is closer to the zero line either for shaft or hole.
Basic shaft: A shaft is called as basic shaft when its upper limit size becomes equal to the basic size. It can be also defined as when upper deviation becomes equal to zero then that shaft is known as basic shaft.
Basic hole: A hole is called as basic hole when its lower limit size becomes equal to the basic size. It can also be defined as when lower deviation becomes equal to zero then that hole is known as basic hole.
Tolerance zone: It is the zone formed by the two limits of size of the part in the graphical representation of tolerance.
Tolerance grade: The tolerance grade is an indication of the degree of accuracy of manufacture and it is designated by the letters IT followed by a number, where "IT stands for International Tolerance grade".
Ex: IT01, IT0, IT1
Standard tolerance unit: It is a unit which is a function of basic size and it is used to find the tolerance value by different tolerance grades. It is denoted by 'i' and expressed in microns.
Basic size: It is a standard size of hole or shaft which is decided during the designing process with which limits are to be decided.
Actual size: It is a final dimension of hole or shaft which is measured after manufacturing process.
Zero line: It is straight line which is drawn to represent the basic size. All limits and fits are explained with the reference of the zero line.
Tolerance: It is defined as permissible variation that are to be given onto the dimensions of the product.
It can be also defined as difference between the maximum size of the object and minimum size of the object.
Generally the tolerance is given in terms of Upper limit and Lower limit in between which final dimension of the object should be.
Upper limit: It is a limit which is given to the dimension of any object to determine the upper limit size or maximum size of that object.
Lower limit: It is a limit which is given to the dimension of any object to determine the lower limit size or minimum size of that object.
Tolerance zone: It defined as an area formed by the difference between maximum dimension and minimum dimension of the object.
Deviation: It is defined as the algebraic difference between limit of shaft or hole and basic size of the shaft or hole.
There are two types of deviations. They are i) Upper deviation ii) Lower deviaton
Upper deviation: It is defined as the difference between upper limit size and the corresponding basic size. It is represented by ES for hole and es for shaft. It is positive when the upper limit size is greater than the basic size. It is negative when the upper limit size is less than the basic size.
Upper deviation = Upper limit size - Basic size
Lower deviation: It is defIned as the difference between lower limit size and the corresponding basic size. It is represented by EI for hole and ei for shaft. It is positive when the lower limit size is greater than the basic size. It is negative when the lower limit size is less than the basic size.
Lower deviation = Lower limit size - Basic size
The tolerance is also defined in terms of upper deviation and lower deviation. It is given as
For shaft
IT = es - ei ( upper deviation - lower deviation)
For hole
IT = ES - EI
Fundamental deviation: It is a deviation either upper deviation or lower deviation which is closer to the zero line either for shaft or hole.
Basic shaft: A shaft is called as basic shaft when its upper limit size becomes equal to the basic size. It can be also defined as when upper deviation becomes equal to zero then that shaft is known as basic shaft.
Basic hole: A hole is called as basic hole when its lower limit size becomes equal to the basic size. It can also be defined as when lower deviation becomes equal to zero then that hole is known as basic hole.
Tolerance zone: It is the zone formed by the two limits of size of the part in the graphical representation of tolerance.
Tolerance grade: The tolerance grade is an indication of the degree of accuracy of manufacture and it is designated by the letters IT followed by a number, where "IT stands for International Tolerance grade".
Ex: IT01, IT0, IT1
Standard tolerance unit: It is a unit which is a function of basic size and it is used to find the tolerance value by different tolerance grades. It is denoted by 'i' and expressed in microns.
Limits and Fits
Friday, 5 July 2013
In manufacturing process after manufacturing the product we need to check the dimensions of the product.
But any manufacturing process is not perfect to produce the product with exact dimensions means higher accuracy. It means we shall be getting the errors on the dimensions of the product. Some time we shall be getting the dimensions more than the required dimensions and some time we shall be getting dimensions less than the required dimensions. So, no manufacturing process is perfect to get perfect dimensions for a required product.
After manufacturing process even if you are getting the errors in the dimensions of the product, those errors can be acceptable up to certain limit. These limits are decided during the designing process. Here the limits means during the designing process certain maximum and minimum dimensional values will be given to compensate the errors that we are getting on the dimensions of the product. If the final dimensions of the product is lying in between that limit values, then the product can be useful for the required assembly. So, permissible variations are allowed on the dimensions of any product.
The permissible variation that can be allowed on the dimensions of the product is known as Tolerance. The tolerance is designated by IT. The tolerance is given to the dimension of the product in terms of Upper Limit and Lower Limit. From these limits we can have the maximum size and minimum size of any product.
The limits and fits are explained by taking the assembly of shaft and hole assembly for easy understanding purpose. There is special terminology is there to understand limits and fits by a simple shaft and hole assembly.
But any manufacturing process is not perfect to produce the product with exact dimensions means higher accuracy. It means we shall be getting the errors on the dimensions of the product. Some time we shall be getting the dimensions more than the required dimensions and some time we shall be getting dimensions less than the required dimensions. So, no manufacturing process is perfect to get perfect dimensions for a required product.
After manufacturing process even if you are getting the errors in the dimensions of the product, those errors can be acceptable up to certain limit. These limits are decided during the designing process. Here the limits means during the designing process certain maximum and minimum dimensional values will be given to compensate the errors that we are getting on the dimensions of the product. If the final dimensions of the product is lying in between that limit values, then the product can be useful for the required assembly. So, permissible variations are allowed on the dimensions of any product.
The permissible variation that can be allowed on the dimensions of the product is known as Tolerance. The tolerance is designated by IT. The tolerance is given to the dimension of the product in terms of Upper Limit and Lower Limit. From these limits we can have the maximum size and minimum size of any product.
The limits and fits are explained by taking the assembly of shaft and hole assembly for easy understanding purpose. There is special terminology is there to understand limits and fits by a simple shaft and hole assembly.
Introduction to Metrology:
Thursday, 4 July 2013
Metrology is a science of measurements. It deals with how to measure the various dimensions of any product and various instruments used for measuring the dimensions. The word Metrology came from the Greek word Metron which means measure. So it is called as Metrology. Metrology deals with all the instruments which are used to measure linear dimensions and non linear dimensions. Examples for linear dimensions are length, width, breadth, thickness, diameter etc. Examples for non linear dimensions are angular measurements. Learning Metrology plays a major role for ones who works in manufacturing industries. In industries after manufacturing the product we have to check the dimensions of the product whether we got the exact dimensions or not. This knowledge can be obtained by learning Metrology. Metrology explains the working principles of various measuring instruments used for finding the various dimensions of the manufactured product.
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