Tolerances MCQ Quiz in తెలుగు - Objective Question with Answer for Tolerances - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Explanation:

Tolerance of hole = 15.05 – 15.03 = 0.02 mm

∴ Tolerance of hole = 20 microns

Now,

Tolerance of shaft = 60 microns

a + 20 + b = 60

a + b = 40

Also, it is given that maximum clearance is 30 microns.

Thus,

Upper limit of hole – lower limit of shaft = 30

20 + b = 30

b = 10 microns

& thus, a = 30 microns

Since,

Allowance = Minimum clearance or maximum interference

For a transition fit.

Allowance = Maximum interference

Allowance = 20 + a

∴ Allowance = 20 + 30 = 50 microns

Concept:

The value of tolerance grade can be found by, \(10{\left( {1.6} \right)^{\left( {ITn - IT6} \right)}}\)

Here, the value for the tolerance grade IT-5 is \(10{\left( {1.6} \right)^{\left( {IT5 - IT6} \right)}}=10\times 1.6^{-1}=7i\)

where i is the standard tolerance unit or Fundamental tolerance unit

\(i\; = \;0.45\sqrt[3]{D}\; + \;0.001D\;\)  in μm

D = D1 x D2 (D1 and D2 are the nominal sizes marking the beginning and the end of a range of sizes, in mm)

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

Concept:

Tolerance of the shaft is given by:

Tolerance = upper limit - lower limit

Calculation:

Given:

\(\phi \;25_{ -0.02}^{ +0.02}\) mm

The upper limit of the shaft will be (25 + 0.02) = 25.02 mm and the base dimension is 25 mm.

The lower limit of the shaft will be (25 - 0.02) =  24.98 mm and the base dimension is 25 mm.

Tolerance is:

Tolerance = upper limit - lower limit

Tolerance = 25.02 - 24.98 = 0.04 mm 

Explanation:

Tolerance

• Tolerance is defined as the total permissible variation of size. In other words, is a range of inaccuracies can be tolerated in measurement. 
• It is the difference between the maximum limit and the minimum limit of size.
• the tolerances determined so that it doesn't affect other factors or the outcome of a process.

Limit

• Two extreme permissible sizes of a part between which the actual size is contained are called limits.
• Ex. Suppose the diameter of the shaft is 10± o.5 mm then, the limit is ± 0.5, the maximum limit of size is + 0.5 mm, The minimum limit of size is - 0.5 mm
• Upper deviation: The difference between the maximum limit of size and the corresponding basic size. (10 + 0.5 = 10.5 mm)
• Lower deviation: The difference between the minimum limit of size and the corresponding basic size. (10 - 0.5 = 9.5 mm)

Fit

• The relationship existing between two parts which are to be assembled with respect to the difference in their sizes before assembly is called a fit.
• The fit signifies the range of tightness or looseness which may result from the application of a specific combination of allowances and tolerances in the design of mating parts.
• There are three general types of fit between the mating parts
  • Clearance fit: A clearance fit is one having limits of size so prescribed that a clearance always results when mating parts are assembled. Ex. The hole is larger than the shaft. (Easy rotation possible)
  • Transition fit: A transition fit is one having limits of size so prescribed that either a clearance or interference may always result when mating parts are assembled. Ex. The hole is fractionally smaller than the shaft. (medium forced required0)
  • Interference fit: An interference fit is one having limits of size so prescribed that an interference always results when mating parts are assembled. Ex. The hole is smaller than the shaft. ( high force required and friction will be there)

​

Fig: Hole Basis System

Accuracy 

• Accuracy of the instrument may be defined as its ability to respond to a true value of a measured variable under reference conditions. 
• In other words, it can also be explained as the closeness with which an instrument reading approaches the true value of the quantity being measured.
• The accuracy of measurement means conformity to the truth. 
• The accuracy of an instrument may be expressed in different ways, viz, in terms of the measured variable itself, a span of the instrument, upper-range value, percent of scale length of actual output reading. 
• Overall Accuracy For the instruments composed of separate physical units like primary; secondary, manipulation, etc.
• Overall accuracy is expressed by combining individual accuracies of different elements. 
• For pressure spring thermometer having an accuracy of the bulb-capillary system as ±0.5% and accuracy of Bourdon pressure gauge as ±1 %.

Concept:

Go gauge size corresponds to the Maximum Material Condition (MMC) of the Part.

• Upper size limit for Shaft
• Lower size limit for Hole

Calculation:

Size of GO gauge = upper limit of pin + (2 × upper limit of plated thickness)

Size of GO Gauge = 35.003 + (2 × 0.044) = 35.091 mm

Concept:

In engineering, the fit between two mating parts (such as a shaft and a hole) is classified based on the tolerance and allowance. The fit can be a clearance fit, interference fit, or transition fit, and each type of fit has specific characteristics.

Explanation:

Given the following data:

• Basic size of the shaft: 50 mm
• Tolerance of the shaft: ± 0.02 mm
• Basic size of the hole: 50.02 mm
• Tolerance of the hole: ± 0.02 mm

We need to determine the type of fit achieved between the shaft and the hole. To do this, we will calculate the maximum and minimum dimensions of both the shaft and the hole.

Calculation:

Shaft Dimensions:

Maximum dimension of the shaft: \(50 \, \text{mm} + 0.02 \, \text{mm} = 50.02 \, \text{mm}\)

Minimum dimension of the shaft: \(50 \, \text{mm} - 0.02 \, \text{mm} = 49.98 \, \text{mm}\)

Hole Dimensions:

Maximum dimension of the hole: \(50.02 \, \text{mm} + 0.02 \, \text{mm} = 50.04 \, \text{mm}\)

Minimum dimension of the hole: \(50.02 \, \text{mm} - 0.02 \, \text{mm} = 50.00 \, \text{mm}\)

Fit Analysis:

A fit is classified based on the relationship between the maximum and minimum dimensions of the shaft and the hole:

• Clearance Fit: The minimum dimension of the hole is greater than the maximum dimension of the shaft, ensuring a gap or clearance between the parts.
• Interference Fit: The maximum dimension of the hole is less than the minimum dimension of the shaft, ensuring that the parts interfere and require force to assemble.
• Transition Fit: The dimensions overlap, and the fit can result in either a clearance or interference depending on the actual dimensions within the tolerance range.

Based on the calculated dimensions:

• Maximum dimension of the shaft: 50.02 mm
• Minimum dimension of the shaft: 49.98 mm
• Maximum dimension of the hole: 50.04 mm
• Minimum dimension of the hole: 50.00 mm

We can see that:

• The maximum dimension of the shaft (50.02 mm) is less than the maximum dimension of the hole (50.04 mm).
• The minimum dimension of the shaft (49.98 mm) is less than the minimum dimension of the hole (50.00 mm).

Since the minimum dimension of the hole is greater than the maximum dimension of the shaft, there will always be a clearance between the parts. However, since the dimensions are very close, this fit is best classified as a transition fit, which can result in either a slight clearance or a slight interference depending on the actual dimensions within the tolerance range.

Therefore, the type of fit most likely to be achieved is:

Transition Fit

Concept:

• Tolerance is the difference between the upper limit and lower limit of a dimension.
• Tolerance Zone is the zone between the maximum and minimum limit size.
• Unilateral Tolerance: The dimension of a part is allowed to vary only on one side of the basic size, i.e. tolerance lies wholly on one side of the basic size either above or below it. ex. \(15.6_{ -0.02}^{ +0.00}\)
• Bilateral Tolerance: The dimension of the part is allowed to vary on both the sides of the basic size, i.e. the limits of tolerance lie on either side of the basic size. ex. \(15.6_{ -0.02}^{ +0.05}\)

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: A grade is an indication of the level of accuracy.

Concept: 

Let the length 62 ± 0.030 be L, 15 ± 0.02 be A and 45 ± 0.030 be B.

According to figure:

L = A + X + B

X = L - A - B

X_max = L_max - A_min - B_min

X_min = L_min - A_max - B_max

Calculation:

Given:

L = 62 ± 0.030 mm, A = 15 ± 0.02 mm, and 45 ± 0.030 mm.

Xmax = Lmax - Amin - Bmin

X_max = (62 + 0.030) - (15 - 0.02) - (45 - 0.030) = 2.08 mm

Xmin = Lmin - Amax - Bmax

X_min = (62 - 0.030) - (15 + 0.02) - (45 + 0.030) = 1.92 mm

Xmax - Xmin = 2.08 - 1.92 = 0.16 mm = 160 μm.

Concept:

The fundamental deviation of tolerance zone from the basic size is designated by capital letters A, B, C...ZC is provided for holes and small letters a, b, c....zc is provided for shafts.

Limits and Fits are having some grades of fundamental tolerances for hole as well as shaft like IT1,IT2..........IT16, etc.

IT shows the tolerance grade on the respective hole or shaft.

Jig Bush

• Jig bushes are used in jigs for guiding tools like drills, reamers, boring bars, and counter bring tools.
• Jig bushes are mainly used to fulfil the following requirements.
  • To allow easy entry of the tool. For easy entry, jig bushes are provided with a chamfer at the top.
  • Bushes must be easily replaceable. For easy fitting and removal, the outer surfaces of the bushes are slightly tapered.
  • Depending upon the number of operations to be performed, one or more bushes are used on different faces of a jig.
  • The bush plate is generally made of mild steel or cast iron, into which hardened bushes are fitted to guide the tools.

• These drilling jigs are used to machine holes in the mechanical products in order to obtain positional accuracy
• The tolerance grade used for Jig bush is H7h6.