Week 9:- 2D Detailing Challenge

Question No 1: What are the Drawing templates?

ANSWER:

Drawing Templates are the standard drawing files that are used to detail the 3D Models like part modelling, product layout, etc.

Drawing Templates:

• Drawing templates are basically the drawing standards as per customers specifications.
• Drawing templates are format that are used for detailing of different parts or units of the fixture.
• There are N numbers of details that are already available on the templates & are useful for various manufacturing processes such as machining finish, tolerances, surface treatments, material, name of the assemblies, etc.
• Preparing a drawing template at the start of the project can help us save time, as these templates can be used as a start model for detailing for different parts.
• Drawing templates also gives information about the angle projection to be used, views to be considered scaling of the drawing as per the part or unit.

Drawing templates contains a lot of information about the drawing as given below:

• Tool code
• Part number
• Tool name
• Company name
• Title
• Designed and checked by who
• Date
• Mass and density
• Allowance
• Scale

• GD&T
• Roughness Symbols and standards
• Quantity
• Tolerances
• Sheet size and sheet number
• Type of projection (1^st angle or 2^nd angle)
• Notes about surface hardening and stress relieving
• 

Question No 2: What do you understand by angle of projection?

ANSWER:

Angle at which the observer looks at an object and draws it in 2D from 3D from real object to paper is called as angle of projection.

The angles of projection are basically the view formats for orthogonal views of assemblies or panels. First and third angle of projection are majorly used in automotive standards. Understanding the angles of projection helps us to derive the actual image of 2D drawing.

The orthographic projection system is used to represent a 3D object in a 2D plane. The orthographic projection system utilizes parallel lines, to project 3D object views onto a 2D plane. According to the rule of orthographic projection. To draw a projection view of a 3D object on a 2D Plane. The horizontal plane is rotated in the clockwise direction.

Types of Orthographic projection systems are first angle and third angle projection.

1. First Angle Projection:

In the first angle projection, the object is placed in the 1st quadrant. The object is positioned at the front of a vertical plane and top of the horizontal plane. First angle projection is widely used in India and European countries. The object is placed between the observer and projection planes. The plane of projection is taken solid in 1st angle projection.

The object is assumed to be positioned in between the projection planes and the observer. The views are obtained by projecting the image on the respective planes.

Symbol:–

Fig . First Angle Projection

2. Third Angle Projection :

In the third angle projection, the object is placed in the third quadrant. The object is placed behind the vertical planes and bottom of the horizontal plane. Third angle projection is widely used in the United States. The projection planes come between the object and observer. The plane of projection is taken as transparent in 3rd angle projection. The projection of plane is assumed to be positioned in between the observer and the object.

Symbol:–

Fig . Third Angle Projection

Difference between 1^st angle and 3^rd angle of projection:

Fig . Third Angle Projection

Fig . First Angle Projection

Question No 3: What is First angle & third angle projection? And why cant we use the 2^nd angle of projection?

ANSWER:

First Angle Projection:

In the first angle projection, the object is placed in the 1st quadrant. The object is positioned at the front of a vertical plane and top of the horizontal plane. First angle projection is widely used in India and European countries. The object is placed between the observer and projection planes. The plane of projection is taken solid in 1st angle projection.

Third Angle Projection:

In the third angle projection, the object is placed in the third quadrant. The object is placed behind the vertical planes and bottom of the horizontal plane. Third angle projection is widely used in the United States. The projection planes come between the object and observer. The plane of projection is taken as transparent in 3rd angle projection.

why cant we use the 2^nd and 4^th angle of projection:

In Second quadrant, Vertical plane (VP) lies in between object and observer. Therefore, front view of the object will lie on vertical plane whereas top view will lie on horizontal plane. As per rule of projection when horizontal plane is rotated 90 degree in clockwise direction, top and front view will overlap.

Overlapping projection views create confusion in the drawing. Therefore 2nd angle projection system is not used.

Similarly, when object is placed in 4th quadrant both top and front view will overlap. Therefore, fourth angle projection is also not used.

To sum up, because of overlapping of front and top views 2nd and 4th angle projections are not used. First and third angle projection systems are recommended for orthographic projections.

Question No 4: What is GD&T? What are the benefits of GD&T?

ANSWER:

Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering toleracnes and relationships. It uses symbols on drawings and computer-generated three-dimensional solid models that explicitly describe nominal geometry and its allowable variation. It tells the manufacturing staff and machines what degree of accuracy is needed on each controlled feature of the part. GD&T is used to define the nominal (theoretically perfect) geometry of parts and assemblies, to define the allowable variation in form and possible size of individual features, and to define the allowable variation between features.

• Dimensioning specifications define the nominal, as-modeled or as-intended geometry. One example is a basic dimension.
• Tolerancing specifications define the allowable variation for the form and possibly the size of individual features, and the allowable variation in orientation and location between features. Two examples are linear dimenions and feature control frames using a datum ref.

Advantages of using GDnT:

• Saving Money: GD&T enhances design accuracy by allowing for appropriate tolerances that maximize production. For many projects, the process provides extra or bonus tolerances, further increasing cost effectiveness.

• Ensuring Dimensional and Tolerance Requirements: By explicitly stating all design requirements, a thorough GD&T process guarantees accurate fulfillment of all dimensional and tolerance specifications.

• Assisting Digital Design Methods: Clear, concise GD&T data is readily adaptable to digital design programs, including nearly universally used 2D and 3D CAD files.

• Offering Uniformity and Convenience: As a single, consistent language, GD&T reduces guesswork and interpretation while ensuring consistent geometries across design and manufacturing.

• Providing Accurate Communication: Today’s intricate designs demand the most accurate and reliable communication. GD&T enables designers, manufacturers, and inspectors to communicate clearly with one other, saving time and making the process more efficient.

Question No 5: Explain all the symbols used in GD&T?

ANSWER:

Geometric Tolerancing Symbols:

GD&T is feature-based, with each feature specified by different controls. These tolerancing symbols fall into five groups:

Form controls specify the shape of features, including:

• Straightness is divided into line element straightness and axis straightness.
• Flatness means straightness in multiple dimensions, measured between the highest and lowest points on a surface.
• Circularity or roundness can be described as straightness bent into a circle.
• Cylindricity is basically flatness bent into a barrel. It includes straightness, roundness, and taper, which makes it expensive to inspect.

Profile controls describe the three-dimensional tolerance zone around a surface:

• Line Profile compares a two-dimensional cross-section to an ideal shape. The tolerance zone is defined by two offset curves unless otherwise specified.
• Surface Profile creates through two offset surfaces between which the feature surface must fall. This is a complex control typically measured with a CMM.

Orientation controls concern dimensions that vary at angles, including:

• Angularity is flatness at an angle to a datum and is also determined through two reference planes spaced the tolerance value apart.
• Perpendicularity means flatness at 90 degrees to a datum. It specifies two perfect planes the feature plane must lie in between.
• Parallelism means straightness at a distance. Parallelism for axes can be defined by defining a cylindrical tolerance zone by placing a diameter symbol in front of the tolerance value.

Location controls define feature locations using linear dimensions:

• Position is the location of features relative to one another or to datums and is the most used control.
• Concentricity compares the location of a feature axis to the datum axis.
• Symmetry ensures that non-cylindrical parts are similar across a datum plane. This is a complex control typically measured with a CMM.

Runout controls define the amount by which a particular feature can vary with respect to the datums:

• Circular Runout is used when there is a need to account for many different errors, such as ball-bearing mounted parts. During inspection, the part is rotated on a spindle to measure the variation or ‘wobble’ around the rotational axis.
• Total Runout is measured on multiple points of a surface, not just describing the runout of a circular feature but of an entire surface. This controls straightness, profile, angularity, and other variations.

Feature Control Frame (FCF):

• The Feature Control Frame is the notation to add controls to the drawing. The leftmost compartment contains the geometric characteristic. In the example above, it is a location control but it can contain any of the control symbols. The first symbol in the second compartment indicates the shape of the tolerance zone. In this example, it is a diameter as opposed to a linear dimension. The number indicates the allowed tolerance.
• Next to the tolerance box, there are separate boxes for each datum feature that the control refers to. Here, the location will be measured related to datum B and C. Next to the tolerance or a datum feature is an optional encircled letter, the feature modifier.

The following possibilities can occur:

• M means that the tolerance applies in the Maximum Material Condition (MMC)
• L means that the tolerance applies in the Least Material Condition (LMC)
• U indicates an unequal bilateral tolerance, i.e. for a 1 mm tolerance it may specify it as minus 0.20 and plus 0.80.
• P means that the tolerance is measured in a Projected Tolerance Zone at a specified distance from the datum.
• No symbol installs the tolerance regardless of feature size (RFS)
• For this example, if the part is not in MMC, a bonus tolerance can be added proportionally to the deviation from MMC. So if a part is at 90% MMC, the tolerance will also loosen by 10%