Limits, Fits and Tolerances MCQ Quiz in বাংলা - Objective Question with Answer for Limits, Fits and Tolerances - বিনামূল্যে ডাউনলোড করুন [PDF]

Explanation:

Plug gauge is a cylindrical bar with highly finished ends of different diameters is used to check hole diameter.

Important points:

• Snap gauge – For gauging external dimensions
• Plug gauge – For gauging internal dimensions
• Taper plug gauge – For gauging taper holes
• Ring gauge – For gauging external dimensions
• Gap gauge – For gauging gaps and grooves
• Radius gauge – For gauging radii
• Thread pitch gauge – For gauging external dimensions

Explanation:

Radius and fillet Gauge:

• Components are machined to have curved formation on the edges or at the junction, Accordingly, they are called radius and fillets
• They are made of hardened sheet metal each to a precise radius
• They are used to check the radii by comparing the radius on a part with the radius of the gauges
• Application of radius gauge to check the radius formed externally

• Application of a fillet gauge to check the fillet formed on a turned component

Explanation:

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.

They consist of a number of small lengths of steel of different thicknesses with measurements marked on each piece.

• 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.
• For maximum protection, blades are assembled in a protective sheath.
• Blade length – Standard blade lengths are typically around 3-5 inches (75 - 127 mm), but long blades might be 12 inches (304.8 mm) and shorter blades around ¾ - 1 inch.
• The most common standard length of a feeler gauge blade is 100 mm

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.

Radius and fillet Gauge:

• Components are machined to have curved formation on the edges or at the junction, Accordingly, they are called radius and fillets
• They are made of hardened sheet metal each to a precise radius
• They are used to check the radii by comparing the radius on a part with the radius of the gauges
• Application of radius gauge to check the radius formed externally

Weld Gauge: 

• A gauge is an instrument or tool that is usually used to measure the sizes of the things when accuracy is important. When this device is designed for checking the shape and size of welds, known as weld gauge.

Some of the welding gauges are the Bridge cam Gauge, Digital Weld Gauge, Adjustable Fillet Weld Gauge etc.

Explanation:

Allowance:

• Allowance is minimum clearance or maximum interference.
• It can be negative or positive.
• It is independent of tolerance.
• It is the difference between the maximum material limits i.e. it is the difference between the upper limit of the shaft and the lower limit of the hole.

Concept:

Limit, Fits & Tolerances:

Basic size

• Size of a part to which all limits of variation i.e. tolerances are applied. The basic dimension is the theoretical dimension.
• It measured as the size of a shaft or hole from the datum line to zero line.

Tolerance

• It is a permissible or acceptable variation in the dimensions of a part.
• It is calculated by the difference between the upper limit and the lower limit of the part.
• It is also calculated by the difference of Upper deviation and lower deviation of the part.

Fundamental deviation

• The nearest distance from the zero line where the tolerance zone is situated.

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Calculation:

Given:

Basic size of shaft = 35

Upper deviation (U.D) = -0.009

Lower deviation (L.D) = -0.025

Fundamental deviation = Upper deviation = -0.009

Tolerance = (U.D) – (L.D.) = (-0.009) - (-0.025) = 0.016

Concept:

Size of NO-GO gauge = upper limit of hole

The plug and ring gauges are further divided into GO gauges and NO-GO gauges which correspond to the Maximum Material Limit (MML) and Minimum Material Limit (MML) of the component.

Calculation:

Size = 44 + 0.3

∴ Size = 44.3 mm

Explanation:

For making hole and shaft assembly two types of systems is adopted internationally. They are:

• Hole basis system
• Shaft basis system

Hole Basis System:

• In this system, the designation of tolerance of the hole is kept constant and the shaft diameter is varied to obtain the various types of fits.
• The basic size of the hole is taken as the lower size limit of the hole i.e. lower deviation of the hole is zero.
• In general practice, the hole basis system is adopted.
• Various tools like standard drills, reamers, broachers are easily available and shafts are later given tolerance to produce the desired fit.

Shaft Basis System:

• In this system, the size of the shaft is kept constant, and the diameter of the hole is varied to give the various fits.
• The basic size of the shaft is taken as the upper size limit of the shaft i.e. upper deviation of the shaft is zero.

Explanation:

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.

• 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.

Concept:

Fit:

Fit is the relationship between two parts to be assembled, resulting from the difference between their sizes, before assembly.

Clearance fit:

• Clearance is the difference between the size of the hole and the size of the shaft which is always positive.
• Hole diameter is always bigger than the shaft diameter in a clearance fit.
• Here the tolerance zone of the hole will be above the tolerance zone of the shaft.

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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.

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.

Explanation:

• In 50H7s6, the number 50 represents the basic size.
• In this, the capital letter H denotes hole and the small letter s denotes shaft. This combination of H7-s6 denotes the interference fit.
• It can be seen in the table below the various types of fit according to the hole shaft system.

• From the table, it is clear that the size of the hole (H) is less than the size of the shaft (s) hence 50H7s6 represents an interference fit.

Concept:

​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.

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Additional Information

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.

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