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Question 1. What are the drawing templates? Answer 1. Drawing Templates- If compared with verbal or written description, drawing offer far better idea about the shape, size & appearance of any object or simulation or location, that too in quite a less time. Hence it has become the best media of communication not only…
Gaurav Sharma
updated on 20 Oct 2021
Question 1. What are the drawing templates?
Answer 1. Drawing Templates-
If compared with verbal or written description, drawing offer far better idea about the shape, size & appearance of any object or simulation or location, that too in quite a less time. Hence it has become the best media of communication not only in engineering but in almost all fields.
Drawing templates-
Drawing templates may be referenced when creating a new drawing. They automatically create the views, set the desired view display, create snap lines, and show model dimensions based on the template.
Drawing templates contain three basic types of information for creating new drawings.
Use the templates to-
You can also create customized drawing templates for the different types of drawings that you create. For example, you can create a template for a machined part versus a cast part. The machined part template could define the views that are typically placed for a drawing of a machined part, set the view display of each view, place company standard machining notes, and automatically create snap lines for placing dimensions. Creating a template allows you to create portions of drawings automatically, using the customizable template.
Drawing templates has information such as-
Question 2. What do you understand by angle of projection?
Answer 2. Angle of projection-
Views of Orthographic Projection.
Following views are formed of an object in Orthographic Projection.
Generally, the Following Three views are prepared in the orthographic drawing.
Front View:
This view is prepared by placing the object in front. The length and height of an object are shown in this view.
Top View:
This view is prepared by looking to the object from the upper side. The length and breadth of the object are shown in it.
Side View:
This view is prepared by looking to the object from the right side or left side. The breadth and height of the object are shown in it.
Principal Plane-
A plane is an imaginary and invisible clear surface. The drawing constructed on this imaginary curtain is transferred on the drawing shee
For example, if we look at some object through glass or plastic piece, then the picture of the object will be seen there.
This piece will work as a plane.
However, this plane is not a material body.
It is only an imaginary curtain, which is used to give the shape of a drawing by placing it in different positions.
This plane can be put in different positions.
However, the plane placed in the following positions is called the Principal Plane.
Besides such positions, the plane will be called Auxiliary Plane.
Frontal Plane-
Such a plane which is placed in front of an object, while projections are drawn, is called the Frontal plane.
Profile Plane-
Such a plane which is placed to the right or left of an object. Side view of the object is drawn on this plane.
Horizontal Plane-
This is a plane which is placed upward or downward in the horizontal position of an object. Top view of the object is constructed on this plane.
Drawing of Orthographic Projection
For drawing Orthographic Projection, different planes are placed in a particular order.
Then a specific view is drawn through every plane.
A plane is placed in the following two Methods.
Dihedral Angle-
In this method, two principal planes are kept perpendicular to each other. One of these planes is Frontal, while other is horizontal.
Four right angles are obtained in this way which is called Dihedral Angle.
Each right angle is called a quadrant. The object is placed in any of these right angles to take orthographic projection.
The front view is taken on the frontal plane, and the top view is taken on the horizontal plane.
Profile plane is used to take side views.
This plane is held perpendicular at the ends of the other two planes.
Trihedral Angle-
In this method, all the three Principal planes are taken perpendicular to one another, and eight right angles are formed.
Thus, these are called Trihedral angle.
Each right angle is called an Octant. An object is placed in any of these right angles to take orthographic projection.
The front view is taken on the frontal plane, and the top view is taken on the horizontal plane. Profile plane is used to take side views.
Systems of Orthographic Projection-
To prepare an orthographic drawing, the selection of one quadrant of dihedral and or one octant of a trihedral angle is made.
In this way the following four systems are formed:
Generally, First Angle System and Third Angle System are used. It is because in the Second Angle System and Fourth Angle System, the lines of views of the object overlap.
Therefore, clear pictures cannot be obtained.
1. First Angle System-
The views of an object should be taken by placing it in the first quadrant of dihedral and or first octant of a trihedral angle.
Such a system is called First Angle System.
By taking the Front view on the frontal plane, top view on the horizontal plane and side view on the Profile plane, the planes are then straightened by rotation.
In this way, the front view comes over the top view; side view comes beside the front view.
Characteristics of First Angle Projection-
2.Third Angle System-
If the views of an object are taken by placing it in the third quadrant of dihedral or third octant of a trihedral tingle.
Such a system is called Third Angle System.
Here, front view forms on the frontal plane, top view forms on the horizontal plane and side view forms on the profile plane.
After making the views, the planes are set straight by rotation.
In this way, the top view comes over the front view, while side view forms by the side of front view.
Characteristics of Third Angle Projection-
Rules of Orthographic Drawing-
Following rules should be followed while forming orthographic drawing.
Selection of View-
Following points should be kept in mind at the selection of view,
Question 3. What is the First angle & Third angle projection? and why can't we use the 2nd and 4th angle of projection?
Answer 3. 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.
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.
Difference between First Angle Projection and Third Angle Projection-
First Angle Projection-
Third Angle Projection-
Similarities Between First Angle and Third Angle Projection
Reason of not using Second and Fourth Angle Projection-
The second and fourth angle projection system has some limitations. Therefore only First and Third angle projection Systems are used to prepare engineering drawings.
To understand why 2nd and 4th angle projection are not used? Firstly we need to understand the concept behind the orthographic projection system.
How does Projection System work?
Let’s consider a point in A and B in 1st and 3rd quadrant respectively. As per the rule of projection, to bring drawing views from three dimensional to two-dimensional planes. Horizontal plane (HP) is rotated in the clockwise direction.
As shown, Point A in 1st quadrant lies in between observer and projection plane. Therefore, the Front view of point A will be in a vertical plane (V.P.) and the top view will be on a horizontal plane.
Similarly, Point B in 3rd quadrant can be projected on the horizontal and vertical plane.
Why Second and Fourth angle Projection Systems are not used?
To understand why the 2nd and 4th angle projection system are not used. We will repeat the above experiment in the second and fourth quadrant.
Let’s consider rectangular parts X and Y are placed in 2nd and 4th quadrant respectively.
In the Second quadrant, vertical plane (VP) lies in between object X and observer. Therefore, the front view of object x will lie on a vertical plane whereas top view will lie on a horizontal plane. As per the rule of projection when a horizontal plane is rotated 90 degrees in a clockwise direction, top and front view will overlap.
Overlapping projection views create confusion in the drawing. Therefore the 2nd angle projection system is not used.
Similarly, when the object is placed in 4th quadrant both top and front view will overlap. Therefore, fourth angle projection is also not used.
Hence, Because of the overlapping of front and top views 2nd and 4th angle projections are not used.
Question 4. What is GD&T? What are the Benefits of GD&T?
Answer 4. Geometric Dimensioning and Tolerancing (GD&T)-
Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering tolerances. It uses a symbolic language on engineering 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 and precision 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.
There are some fundamental rules that need to be applied:
Benefits of GD & T-
Question 5. Explain all the symbols used in GD&T?
Answer 5. Symbols used in GD&T-
GD&T has 14 symbols out of which 10 are most commonly used features. They are categorized base on a form, orientation, location, profile and run out. They are described below.
Form:
Form controls the shape of surfaces. It does allow datum reference.
1) Straightness- In this feature, all the elements are supposed to be in a straight line. It is used for a line to communicate the variation allowed in a line, hence maintaining it straight. It doesn't require a datum. If it is to be used for a cylinder, it is given along with the diameter dimension. It controls each dimension separately.
2) Flatness- In this feature, all the elements are supposed to be in the same plane. Flatness error is calculated by the difference in the highest and lowest points on the plane. You are trying making sure that any point along the surface does not go above or below the tolerance zone. This feature doesn't require any reference.
3) Circularity- Circularity requires no datum. Circularity ensures all the points to be equidistant from the center. Circularity error is the radial distance between coaxial diameters. it limits the circularity error.
4) Cylindricity- This feature ensures that the surface of the cylinder is smooth and within the tolerance zone. Each surface is at a fixed distance from the axis of the cylinder in this feature. It does not require a datum.
Orientation:
5) Perpendicularity- When this feature is applied to a surface, the tolerance zone is between two parallel surfaces perpendicular to the datum surface. It requires a datum surface.
6) Parallelism- When this feature is applied to a surface, the tolerance zone is between two parallel surfaces parallel to the datum surface. It basically ensures that all the points on the referenced surface lies in the tolerance zone at a certain distance away from the datum surface. It also ensures that the surface to be referenced is parallel to the datum surface. Parallelism is quite simple to measure.
7) Angularity- Angularity is a feature that is specified between two lines. It requires a datum reference from which the angular tolerance is maintained. In case of a plane, angularity feature maintains the angular tolerance between two planes.
Profile:
8) Profile of a surface- Profile of a line is usually used at a place where we require a surface to be in the tolerance range. In this case, the profile directly mimics the design of the surface. Every point of the surface should fall within the tolerance zone. For example, if a callout is given on fillet of a weldment, each point on the surface should fall in the tolerance zone. It is used only for advanced curve surfaces. A CMM is used to track the entire surface.
9) Profile of Line- This feature is used at places where a curve is to be maintained within the tolerance zone. The tolerance zone is two parallel curves from the main curve. It is used for advanced curves. This tolerance zone may or may not be referenced by a datum.
Location:
10) Position- Position tolerance shows the exact location of a FOS(a feature of size) with respect to a datum. It tells us how far feature location can vary from its true position. It requires datum for reference.
11) Concentricity- Concentricity feature ensures the smoothness of a cylindrical surface with respect to a datum surface. A surface is chosen as a datum. The axis about which this surface acts as a datum axis for the feature we wish to control. The feature must fall in the tolerance zone. It is very difficult to maintain concentricity as it is not to be checked directly w.r.t a surface but w.r.t an axis derived from another surface.
12) Symmetry- Symmetry feature ensures symmetry of a 3d object about a virtual datum plane. Points from either surface are calculated using the CMM and checked if they fall in the positive and negative side of the tolerance zone. Symmetry is very difficult to calculate as it does not have a fixed surface about which we can check the deviation.
Runout:
13) Circular Runout- Runout feature is used to check how much one feature of a part varies with respect to another when the part is rotated about a datum axis. It is basically used to check how much a part wobbles. Runout can be called out on any feature that is rotated about an axis. Runout is measured using a simple height gauge on the reference surface.
14) Total Runout- Total Runout is how much a surface or feature varies with respect to a datum when the part is rotated 360 degrees about datum axis. It controls both amounts of variation in the surface when the part is rotated and also the variation in the axial dimension.
Other Symbols used in GD&T
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