CAD Questions

In Mechanical Design we have to face lot of question in interview which can give us job and wrong impression can be disqualify us in interview. So its too important to have proper technical skill and communication skills .

For technical skill we have some interview question which can help to clear mechanical design interviews. 

S.N	Questions	Option A	Option B	Option C	Option D
1.	Which Drawing standards also called as world standard?	ANSI	ISO	DIN	IS
2.	Which drawing standard is primarily used in US?	ANSI	ISO	DIN	IS
3.	Revision letter in the drawing are used?	To identify the name of draftsman	To identify a change in the 3D model	To identify a change or revision to a drawing	All the above
4.	BOM (Bill of material) or part lists should contain?	Part number part name, Material and quantity	Part Name, Zone, Date, Quantity	Scale, Drawing number, Material	All the above
5.		Perpendicular tolerance	Parallel tolerance	Angular tolerance	None of Above
6.	The simplest method of the tolerance stack up analysis is?	Worst Cone	Worst line	Best case	Worst Case
7.	___is that condition where the axes of two or more surfaces of revolution are coincident.	Circularity	Coincidence	Circular	Coaxially
8.		Profile	Runout	Orientation	Location
9.		Form	Profile	Circularity	Orientation
10.	This image represents?	MMC	LMC	Bonus	Profile

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Concentricity in GD&T

Concentricity in GD&T

Concentricity:- Concentricity is indicated by two concentric circles. Concentricity also known as coaxially. It controls tolerance of central axis of the referenced feature, to a datum axis.
*Concentricity describes a condition in which two or more feature, in any combination, have a common axis.

The need for this symbol has been challenged, but it is still used to specify concentricity. Care should be taken to avoid the use of this symbol if the needed control can be position or runout tolerances.

Concentricity is a 3-Dimensional cylindrical tolerance zone that is defined by a datum axis where all the derived median points of a referenced circular feature must fall into. the median points of the reference surface cross sections form the theoretical axis that must be in this tolerance zone.

When Used:

Due to its complex nature, Concentricity is usually reserved for parts that require a high degree of precision to function properly. Transmission gears, which need to always be coaxial to avoid oscillations and wear, may require concentricity to ensure all the axes line up correctly. Equal mass or inertial concerns are one of the leading causes for the concentricity callout. Any application where the median points of a feature need to be controlled relative to a datum would require cylindricity. However in many cases, the use of runout or true position can replace the need for concentricity and be much easier to measure for.

Example:

An intermediate shaft in a transmission is composed of two different diameter sections which are coaxial. Datum A is the drive side and relatively fixed with bearings to the housing, The referenced surface B is desired to be concentric with Datum A to avoid oscillations at high speed.

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Depth/Deep Symbol in GD&T

Depth/Deep

Depth/Deep  is used to indicate that a dimension applies to the depth of a feature and it is placed in front of the depth value in such
applications as for counterbore and hole.

• Symbol size and details are in Pic.
• h indicate font size if dimension.

EX-

Here is two dia shown in top view, one is dia .750 and second is dia 1,where first dia is throughout and second is counterbore which is only .625 deep.











Note- Tolerence also applied as per requirement or as per standard in depth.



  

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Square symbol in GD&T

Square

Square Symbol is used to indicate that a single dimension applies to a square shape and the symbol precedes the dimension with no space between.The size of Square box used to indicate square have same height (h) and width(h) as font size used for dimension (h).

EX- The Square symbol applies to sqaure features as diameter symbol applies to cylinderical features.

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Geometric Dimensioning and Tolerancing (GD&T)

GD&T-

• GD&T is a symbolic language for defining and communicating engineering tolereances.
• Used to specify the size, shape, form, orientation, and location of features on a part.
• GD&T was created to insure the proper assembly of mating parts, to improve quality, and to reduce cost.
• Drawings with properly applied geometric tolerancing provide the best opportunity for uniform interpretation and cost-effective assembly.

History-
DuringWorldWar II, the United States manufactured and shipped spare parts, Many of these parts were made to specifications but would not assemble.They recognized that producing parts that do not properly fit or function is a serious problem since lives depend on equipment that functions properly. To find a way to insure that parts would properly fit and function every time. The result was the development of GD&T.
GD&T has been credited to a man named "Stanley Parker", who developed the concept of "true position".
Ultimately, the USASI Y14.5–1966 document was produced on the basis of earlier standards and industry practices. The following are revisions to the standard:
ANSI Y14.5–1973 (American National Standards Institute)
ANSI Y14.5M–1982
ASME Y14.5M–1994 (American Society of Mechanical Engineers)
The 1994 revision is the current, authoritative reference document that specifies the proper application of GD&T.

Three important advantages over the coordinate tolerancing system:

• The cylindrical tolerance zone
• The maximum material condition
• Datums specified in order of precedence

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(3) GD&T Symbols - Diameter, Radius, Controlled Radius and Spherical Radius/Dia

• Diameter (ø) -
  Indicates a circular feature when used on the field of a drawing or indicates that tolerance is  diametrial when used in a feature control frame.
                 OR
   Diameter symbol replaces the word "Diameter". It should be used anywhere there is a diameter on the drawing,abd when a tolerence zone is cylindrical.
  
  Ex-
  
  
  
• Radius (R)-   A straight line extending from the center of an arc or circle to its surface.
  
  
  EX-
  
  
  
  
  

Controlled Radius (CR)-  Creates a tolerance zone defined by two arcs (the minimum and maximum radii) that are tangent to the adjacent surfaces. Where a controlled radius is specified, the part contour within the crescent-shaped tolerance zone must be a fair curve without flats or reversals. Additionally, radii taken at all points on the part contour shall neither be smaller than the specified minimum limit nor larger than the maximum limit.
The Abbreviation CR is defined by 1994 standard to indicate a controlled radius dimension.

• Spherical Radius (SR) Or Spherical Diameter (Sø)- 
  
  Spherical Diameter - shall precede the tolerance value where the specified tolerance value represents spherical zone. Also, a positional tolerance may be used to control the location of a spherical feature relative to other features of a part. The symbol for spherical diameter precedes the size dimension of the feature and the positional tolerance value, to indicate a spherical tolerance zone.
  
  SR
  Spherical Radius - precedes the value of a dimension or tolerance.
  
                               OR
  Spherical Features may be dimensioned by giving either the radius of diameter of a sphere.
  
  Ex-
  

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(2)-Basic GD&T (Interview Questions)

Q1- How will you define GD&T?
Ans- GD&T is Geometric Dimensioning and Tolerancing.
        Methods of showing tolerences using symbols.
        it is engineering communication tool using symbols.
        GD&T ensures repeatability and interchangeability.

Q2-How will you classify GD&T According to geometry?

Ans- There are five classes according to function of the geometry-

1-Form of geometry-
    A- Flatness      B- Straightness   C- Cylindercity   D- Circularity

2- Orientation of geometry-

    A-Parallelism     B- Perpendicularity    C- Angularity

3-Profile of geometry-

    A-Profile of a line          B-Profile of a surface

4- Control of run out-

    A- circular runout          B- Total Runout

5-Location of geometry-

   A-Position           B- Symmetry    C-Concentricity

Q3- Differentiate b/w Flatness and straightness?

Ans- When cylindrical geometry of shaft subjected to twist or bend,it looses it's straightness. in below setup when dial indicator moved along the shaft, it will show whether the straightness is within tolerance or has deviated. the shaft is not revolving while measurement.

and flatness is straightness of plane profile at each and every point on the surface.

Q4- Differentiate b/w circularity and cylindercity?
Ans- Circularity is about roundness of tapered, concave or convex profile at particular section cylindercity of constant diameter cykunder along the length.
the dial indicator attached to a fixture with high precision revolves along the round profile to examine the roundness. in cylendercity it moves alongthe length while revolving to measure the roundness.



Q5- What do you mean by Reference Dimension?
Ans-     Symbol for Reference Dimension   (XX)
         XX- Value of Dimension.    Ex- (40)
       Reference dimension usually without tolerence, used for information purposes only. it does not givern production or inspection operations.

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(1)-Geometric Dimensioning and Tolerancing (GD&T) Symbol and it's Means

Here we have some important symbol which we used in gd and t. 

             
                          

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