Week 9- Challenge Prashant Mahajan
Q. What are the Drawing templates?
Drawing templates are the standard drawing files that are used to detail the 3D parts like mylars, pins, weldments, blades, pin retainers and L blocks that are designed and 3D finished.
Drawing Templates provides a platform where a designer can convey the details of design of a part or assembly with the help of a drawing.
Drawing Templates contains a lot of information about the drawing as given below:
Scale,
GD&T,
Roughness symbol and standards,
Person who has designed,checked and apprved the drawing,
Part size,
Quantity,
Material,
Tolerances,
Sheet Size,
Type of Projection(1st angle or 3rd angle),
Notes about surface hardening and stress relieving
Project Code
Project Name
Title
Every company has its own standard design template which contains all the symbols and standards that the company follows to detail the parts or assemblies.
Usually, Mylars and Pins are detailed on the A4 sheets while A3 sheets are used to detail the key sheets.
Depending on the size of part or assembly, we can change the scale so that the drawing fits the sheet. We need to make sure that all the details about the drawing like linear dimentions, hole dimentions, GD&T, roughness etc. are clearly visible.
Note: It is very important that while detailing we should check the angle of projection in which customer requires us to give the drawing. According to the customer standards, we should change the drawing angle of projection setting in our sofware and only then we should start detailing. not doing this can lead to errors in manufacturing and increase the ovrall cost.
Q. What do you understand by Angle of projection?
To define an object, technical drawings use 2 dimentional views. This is called orthogonal projection. Angle of projection is of the quadrant in which we have kept the object. The projection of the object is projected on to the planes as it is viewed by the observer. Images projected on the horizontal planes are rotated clockwise so that the projections come on the same plane.
Orthogonal projection uses diffrent methods to project the 3D object namely:
First Angle Projection
First angle of projection is a type of orthographic projection in which the object lies between the observer and the plane of projection. In this projection, the top view comes onthe bottom and the bottom view comes on the top of the front view. Similarly, the left view of the object is projected on the right and right view projected on the left. It is most commonly used in Europe and Asia region. Drawing templates contain the symbol of the type of projection to be used to project the images. Knowledge about the angle of projection symbols can help us identify the angle of projection in which the drawing is to be made.
Third Angle Projection
Third angle of projection is a type of orthographic projection in which plane of projection lies between object and observer. In this, the top view comes on the top of front view and the bottom view on the bottom. Similartly, left view is projected on the left and right on the right side of front view.
It is used mostly in USA and Australia.
Differences between the First angle projection and third angle of projection:
1) In first angle projection object lies in the first quadrant while in third angle of projection, object lies in the third quardant.
2) In first angle projection, the top view comes on the bottom and the bottom view comes on the top of the front view while in third angle projection the top view comes on the top of front view and the bottom view on the bottom.
3) Difference in symbols of first and third angle are given
4) Plane of projection is assumed to be non transparent in first angle projection while it is assumed to be transparent in third angle projection.
These two projections types vary from customer to customer depending on their standards. Knowing about the angles of projection helps us to get an image of the object for which drawings are drawn.
Q. What is the First angle & Third angle projection? and why can\'t we use the 2nd and 4th angle of projection?
First angle of Projection
First angle of projection is a type of orthographic projection in which the object lies between the observer and the plane of projection. In this projection, the top view comes onthe bottom and the bottom view comes on the top of the front view. Similarly, the left view of the object is projected on the right and right view projected on the left. It is most commonly used in Europe and Asia region. Drawing templates contain the symbol of the type of projection to be used to project the images. Knowledge about the angle of projection symbols can help us identify the angle of projection in which the drawing is to be made.
Third angle of Projection
Third angle of projection is a type of orthographic projection in which plane of projection lies between object and observer. In this, the top view comes on the top of front view and the bottom view on the bottom. Similartly, left view is projected on the left and right on the right side of front view.
It is used mostly in USA and Australia.
First angle projection and third angle projection are depicted below:
2nd angle of projection and 4th angle of projection cannot be used as angles of projection because according to the rule the view projected on the horizontal plane is rotated clockwise by 90 degrees to get them on the same plane, which will overlap with the top view in 2nd and 4th angle of projection. Hence, they are not used as angles of projection. it has been explained diametrically below:
Q. What is GD&T? What are the benefits of GD&T?
Symbols of GD&T come to mind first when we talk about GD&T. GD&T is not just about symbols. GD&T is the abbreviated form of Geometric Dimensioning and tolerancing. It is a system of defining and communicating engineering tolernces. It uses symbols to describe the nominal value and to what variation can it be made. GD&T helps to covey to the operator as to how much precision and accuracy is required in a particular feature of a part. GD&T can add value and reduce cost at the same time through producibility. In GD&T, there are a total of 14 symbols each of which has a specific function.
These symbols are placed in the first compartment which show the type of tolerance to be applied. The characteristics are grouped into diffrent features like form, orientation, location, runout. Their primary use and description is shown in the table. GD&T is applied to features using a feature control frame. Most used tolerance categories are form, location and orientation. Among the 14 symbols that are there, the most used symbols are only 10.
Figure above shows an object being controlled by three datums and a control frame. By datums, we mean the reference points that we take to measure the basic dimentions, A being the 1st datum, B being the second and C the third datum.
Form tolerances control the shape of the part
Orientation tolerances control the tilt of the part and has to do with the angle at which particular part is tilted.
Location toleraces deal with the location of a particular feature and has to do with linear dimensions of a part. Any plane or side is taken as a reference and a corresponding linear dimetion is drawn metioning the tolerance and feature applied.Profile locates feature surfaces. Profile is one of the strongest features and controls form and orientation.
Benefits of GD&T:
1) GD&T is a language of engineers which they use to convey the tolerances and feaures in an easy and precise way.
2) GD&T can increase quality, add value and at the same time reduce cost.
3) It enhances design accuracy.
4) It maintains uniformity in drawings and makes it possible for comple designs to be implemented using diffrent features.
Q. Explain all the symbols used in GD&T?
GD&T has 14 symbols out of which 10 are most commonly used features. They are categorised base on form, orientation, location, profile and runout. They are described below:
Form:
Form controls shape of surfaces. It does allow datum reference.
1) 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 doesnt require any reference.
2) Straightness- In this feature, all the elements are supposed to be in straight line. It is used for a line to comunicate the variation allowed in a line, hence maintaining it straight. It doesnot require a datum. If it is to be used for a cylinder, it is given along with the diameter dimension. It controls each dimention separately.
3) Cylindricity- This feature ensures that the surface of cylinder is smooth and within the tolerance zone. Each surface is at a fixed distance from the axis of cylinder in this feature. It does not require a datum.
4) Circularity- Circularity requires no datum. Circularity ensures all the points to be equidistant from centre. Circularity error is the radial distance between coaxial diameters. it limits the circularity error.
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 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 anglular tolerance is maintained. In case of a plane, angularity feature maintains the angular tolerance between two planes.
8) Position- Position tolerance shows the exact location of a FOS(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.
Profile:
9) 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 th surface should fall in the tolerance zone. It is used only for advanced curve surfaces. A CMM is used to track the entire surface.
10) 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.
Runout:
11) 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 amount of variation in the surface when the part is rotated and also the variation in the axial dimension.
12) Circular Runout- Runout feature is used to check how much one feature of a part varies with respect to another when the part is otated 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.
Location(Derived Median points):
13) 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 is 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 a axis derived from another surface.
14) Symetry- Symetry feature ensures symetry of a 3d object about a virtual datum plane. Points from the either surface are calculated using the CMM and checked if they fall in the positive and negative side of tolerance zone. Symetry is very difficult to calculate as it does not have a fixed surface about which we can check the deviation.