Limits, Fits and Tolerances MCQ Quiz - Objective Question with Answer for Limits, Fits and Tolerances - Download Free PDF

Concept:

Fit is a relationship that exists between two mating parts a hole and a beam with respect to their dimensional difference before assembly.

There are three types of fits.

Clearance fit: 

• In this fit the size of the Hole is always greater than the size of the beam. Clearance is the difference between the size of the hole and the size of the beam which is always positive. Here the tolerance zone of the hole will be above the tolerance zone of the beam.
• Examples: Slide fit easy sliding fit running fit slack running fit and loose running fit.

Interference fit: 

• In this fit the size of the Hole is always less than the size of the beam. Interference is the difference between the size of the hole and the size of the beam which is always negative i.e. beam is always larger than the hole size. Here the tolerance zone of the hole will be below the tolerance zone of the beam.
• Examples: Shrink fit heavy drive fit and light drive fit.

Transition fit: 

• It may sometimes provide clearance and sometimes interference. Here the tolerance zones of the hole and beam will overlap each other.
• Examples: Tight fit and pushfit wringing fit press fit.

Explanation:

Interference Fit:

• An interference fit, also known as a press fit or friction fit, is a form of fastening between two parts, such as a shaft and a hole, which is achieved by making the parts have slightly differing dimensions.
• The shaft is slightly larger than the hole, and when the two parts are pressed together, the resulting friction holds them in place.
• In an interference fit, the shaft is manufactured slightly larger than the hole into which it will be inserted.
• When force is applied to insert the shaft into the hole, the material deforms slightly, creating a tight fit.
• The friction between the surfaces of the shaft and the hole prevents relative motion between the parts.

Advantages:

• Uniform stress distribution at the joint: The interference fit ensures that the stress is uniformly distributed across the contact surface, enhancing the joint's strength and durability.
• Prevention of relative motion between parts: The tight fit prevents any relative motion between the shaft and the hole, eliminating issues such as wear and tear due to movement.
• Increased load-bearing capacity: The interference fit enhances the load-bearing capacity of the joint, making it suitable for applications that involve high loads.

Disadvantages:

• Difficulty in assembly and disassembly: Due to the tight fit, assembling and disassembling parts can be challenging and may require special tools or techniques.
• Potential for damage during assembly: The force required to press the parts together can cause damage if not done correctly.

Applications: Interference fits are commonly used in applications where a strong, permanent joint is required, such as in gears, wheels, pulleys, and bearing assemblies.

Concept:

Clearance Fit:

• In a clearance fit, the largest shaft is smaller than the smallest hole. The difference between the sizes is known as clearance. For a given hole and shaft, the clearance can be calculated as follows:

Minimum Clearance:

• The minimum clearance is the difference between the smallest hole size and the largest shaft size.

Maximum Clearance:

• The maximum clearance is the difference between the largest hole size and the smallest shaft size.

Calculation:

Given:

Hole size: Ø50(+0.050/0.000) mm

Minimum clearance: 0.02 mm

Tolerance on the shaft: 0.03 mm

Minimum hole size = 50.000 mm
Maximum hole size = 50.050 mm

Let the minimum shaft size be X mm
Maximum shaft size = X + 0.03 mm

Minimum hole size - Maximum shaft size = Minimum clearance

50.000 mm - (X + 0.03 mm) = 0.02 mm

50.000 mm - 0.02 mm = X + 0.03 mm

49.980 mm = X + 0.03 mm

X = 49.950 mm

Determine the maximum clearance.

• Maximum hole size - Minimum shaft size = Maximum clearance
• 50.050 mm - 49.950 mm = 0.100 mm

The maximum clearance between the hole and the shaft is 0.100 mm.

Explanation:

Tolerance is the difference between the upper limit and lower limit of a dimension.

They are of two types:

Unilateral Tolerance: 

The dimension of a part is allowed to vary only on one side of the nominal size, i.e. tolerance lies wholly on one side of the nominal size either above or below it.

Bilateral Tolerance:

The dimension of the part is allowed to vary on both sides of the nominal size, i.e. the limits of tolerance lie on either side of the nominal size.

Explanation:

Type fit use for a slide journal bearing and sliding gears on shaft:

• In mechanical engineering, journal bearings and sliding gears on shafts require specific types of fits to ensure proper operation, minimize wear, and maintain alignment.
• It is because they provide the necessary clearance to allow for smooth sliding motion while maintaining alignment and reducing wear.
• The fit type is usually specified by the hole and shaft tolerance grades, such as H8 and e8.

H5-h5

• H5/h5 fits are precision fits with very tight tolerances, used for applications requiring high accuracy and minimal clearance.

H6-j6

• H6/j6 fits are also tight fits, but with slightly more clearance than H5/h5. They are used in applications requiring good alignment and low clearance.

H8-b7

• H8/b7 fits provide moderate clearance, used for applications where some movement is acceptable but not significant.

Explanation:

Fit is a relationship that exists between two mating parts, a hole, and a shaft, with respect to their dimensional difference before assembly.

There are three types of fits.

Transition fit: It may sometimes provide clearance and sometimes interference. Here the tolerance zones of the hole and shaft will overlap each other.

Examples: Tight fit and push-fit, wringing fit, 

Clearance fit: Clearance is the difference between the size of the hole and the size of the shaft which is always positive. Here the tolerance zone of the hole will be above the tolerance zone of the shaft.

Examples: Slide fit, easy sliding fit, running fit, slack running fit, and loose running fit.

Interference fit: Interference is the difference between the size of the hole and the size of the shaft which is always negative i.e. shaft is always larger than the hole size. Here, the tolerance zone of the hole will be below the tolerance zone of the shaft.

Examples: Press fit, Shrink fit, heavy drive fit, and light drive fit, selective fit, Snap-fit, Force fit

Explanation:

In this capital letter H denotes hole and small letter g denotes shaft. This combination H7-g6 denotes the clearance fit. It can be seen in the table below the various types of fit according to the hole shaft system.

Concept:

Fit is a relationship that exists between two mating parts, a hole, and a shaft, with respect to their dimensional difference before assembly.

• Clearance fit: Clearance is the difference between the size of the hole and the size of the shaft which is always positive. Here the tolerance zone of the hole will be above the tolerance zone of the shaft.

Examples: Slide fit, easy sliding fit, running fit, slack running fit, and loose running fit.

The above-given figure represents the clearance fit because the tolerance zone is not meeting.

• Interference fit: Interference is the difference between the size of the hole and the size of the shaft which is always negative i.e. shaft is always larger than the hole size. Here the tolerance zone of the hole will be below the tolerance zone of the shaft.

Examples: Shrink fit, heavy drive fit, and light drive fit.

• Transition fit: It may sometimes provide clearance and sometimes interference. Here the tolerance zones of the hole and shaft will overlap each other.

Examples: Tight fit and push-fit, wringing fit, press fit.

Calculation:

Given:

Hole dimension: \(\phi 9\begin{array}{*{20}{c}} { + 0.015}\\ { + 0} \end{array}mm\)

Shaft dimension: \(\phi {9^{\begin{array}{*{20}{c}} { + 0.010}\\ { + 0.001} \end{array}}}mm\)

The tolerance zone is overlapping, so it is a transition fit.

Vernier Caliper

Vernier Caliper is a precision instrument that can be used to measure internal and external distances accurately.

A vernier calliper consists of two main parts: The main scale engraved on a solid L-shaped frame and the vernier scale that can slide along the main scale. 

It works on the principle of vernier and can measure the dimensions to an accuracy of 0.02 mm.

The vernier division coinciding with the main scale is the xth division, value = x × 0.02 mm = 0.02x mm.

​ 

Calculation:

Given:

Main scale reading = 20.5 mm

The vernier division coinciding with the main scale is the 9th division, value = 9 × 0.02 mm = 0.18 mm.

Dimension of the object = main scale reading + vernier scale reading = 20.5 + 0.18 = 20.68 mm.

Concept:

Interference fit: Interference is the difference between the size of the hole and the size of the shaft which is always negative i.e. shaft is always larger than the hole size. Here the tolerance zone of the hole will be below the tolerance zone of the shaft.

Maximum Interference = Upper limit of the shaft – Lower limit of hole

Calculation:

Given:

Hole \(30_{ + 0.03}^{ + 0.06}\)  mm, Shaft  \(30_{ - 0.02}^{+ 0.04}\) mm

Upper limit of shaft = 30 + 0.04 = 30.04 mm

Lower limit of hole = 30 + 0.03 = 30.03 mm

Maximum Interference = Upper limit of the shaft - Lower limit of hole

Explanation: ​

Slip gauges:

• Slip gauges are very precisely manufactured for measuring, setting up of sizes and also to calibrate precision measuring instruments or inspection gauges.
• They can be used to measure tolerances in the range of 0.001 to 0.0005 mm very accurately. With the slip gauges, we can measure a finer tolerance limit.
• Therefore, slip gauges are used for checking the accuracy of the limit gauge.

​

Feeler gauges:

• A feeler gauge is a tool used to measure gap widths.
• Feeler gauges are mostly used in engineering to measure the clearance between two parts like spark plug gaps, bearing clearance, the gap between the mating parts, etc.  
• They consist of a number of small lengths of steel of different thicknesses with measurements marked on each piece.

Ring gauges:

• Ring Gages also referred to as Plain Cylindrical Ring Gauges.
• They are used to check the outside diameter limit on manufactured parts.
• When they are used to check a part directly, the cylindrical ring gages are referred to as GO and NOGO.
• The GO ring gauge checks the upper limit of the part tolerance while the NOGO ring gauge checks the lower limit.

​

​Plug gauge:

• A plug gauge is a cylindrical type of gauge, used to check the accuracy of holes.
• They are used to check the inside diameter limit on manufactured parts.
• The GO plug gauge checks the lower limit of the part tolerance while the NOGO plug gauge checks the upper limit.

​

Plug Gauges are mainly used for measuring hole dimension. The Go-gauge checks the lower limit of a straight hole and the NO-Go gauge checks the upper limit.

Snap Gauges: Used as a quick means for checking sizes within certain limits by comparing the size of the parts with the opening of the gauge.

Feeler Gauge is used to measure gap width or clearance between the mating parts.

Fillet Gauge: It is also known as Radius gauge. Components are machined to have a curved formation on the edges or at the junction of two parts, which are known as a fillet. The gauges used to check the radius of fillet are fillet gauges.

Explanation:

Manufacturing or Engineering tolerance

Manufacturing or Engineering tolerance is the permissible limit or limits of variation in a physical dimension.

Different type of tolerance has been defined for the manufacturing of any component.

This tolerance grade can be shown by a pre define symbol, a list has been shown below.

Explanation:

Limits and fits comprise 18 grades of fundamental tolerances for both shaft and hole, designated as IT01, IT0 and IT1 to IT16.

These are called standard tolerances.

Grades of Tolerance: Grade is an indication of the level of accuracy.

Concept:

Fit:

• Fit is the relationship between two parts to be assembled, resulting from the difference between their sizes, before assembly. 
• Fit refers to the mating of two mechanical components, manufactured parts are very frequently required to mate with one another.
• They may be designed to slide freely against one another or they may be designed to bind together into a single unit.
• The most common fit found in the machine shop is that of a shaft in a hole.
• Fit represents a degree of tightness or looseness between two mating parts to perform a definite function.

Following fits exist between the shaft and the hole

• Clearance fit:
  • Hole diameter is always bigger than the shaft diameter.
  • Both maximum and minimum clearance are always positive.
• Transition fit:
  • The hole diameter is close to the shaft diameter.
  • Maximum clearance is positive and minimum clearance is negative.
• Interference fit:
  • Hole diameter is always lesser than shaft diameter. 
  • Both maximum and minimum clearances are always negative.