2D Detailing Challenge

What are the Drawing templates?

Drawing templates:

• Drawing templates are basically the drawing standards as per the customer’s specifications.
• Drawing templates are formats that are used for detailing different parts or units of the fixture.
• A drawing template file is a drawing file that has been saved with a . dwt file extension, and it specifies the styles, settings, and layouts in a drawing, including title blocks
• There are ‘n’ numbers of details that are already available on the template & are useful for various manufacturing processes, such as, machining finish, tolerances, surface treatments, material, name of the parts, 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 starter model for detailing for different parts.
• Drawing templates also give information about the angle of projection to be used, views to be considered, scaling of the drawing as per the part or unit.
• A separate template is prepared for each sheet size like A1, A2, A3, A4 & so on.

What do you understand by Angle of projection?

Angles of Projection:
The angle at which an observer draws an object to convert it from 3D to 2D plane such as real object image to a plane paper is known as the angle of projection.

Angles of projection are basically the view formats for orthogonal views of assemblies or parts.

Orthographic projections: It is a technical drawing in which different views of an object are projected on different reference planes observing perpendicular to the respective reference plane.

Different reference planes are horizontal plane (HP), vertical frontal plane (VP), side or profile plane.
Different views are front view (FV), top view (TV) & side view (SV).

-FV is a view projected on VP.
- TV is a view projected on HP.
- SV is a view projected on PP

Important terms of orthographic projections:

1.Plane:

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:
In this, the object is assumed to be positioned in the first quadrant & is shown in the figure. The object is assumed to be positioned in between the projection planes & the observer. The views are obtained by projecting the images on the respective planes.

In this type of projection, the object is imagined to be in the first quadrant. Because the observer normally looks from the right side of the quadrant to obtain the front view, the objects will come in between the observer and the plane of projection. Therefore, in this case, the object is imagined to be transparent, and the projectors are imagined to be extended from various points of the object to meet the projection plane. When these meeting points are joined in order on the plane they form an image, thus in the first angle projection, any view is so placed that it represents the side of the object away from it.

Third Angle Projection:
Here the object is assumed to be in the third quadrant. i.e. the object behind the vertical plane & below the horizontal plane. In this projection technique, placing the object in the third quadrant puts the projection planes between the viewer & the object & is shown in the figure.

In this type of projection, the object is imagined to be in the third quadrant. Again, as the observer is normally supposed to look from the right side of the quadrant to obtain the front view, in this method, the projection plane comes in between the observer and the object. Therefore, the plane of projection is assumed to be transparent. The intersection of this plan with the projectors from all the points of the object would form an image on the transparent plane.

Why 2 & 4 angle projection is not used?

The second & fourth angles of projection systems is not used to draw engineering drawings because of the limitation of overlapping projection views.

How orthographic projection system works?
Let’s consider a point A & B in the 1 & 3 quadrants respectively. As per the rule of orthographic projection, to bring drawing views from three-dimensional to two-dimensional planes. The horizontal plane (HP) is rotated in the clockwise direction.

As shown in the below image, point A in the 1 quadrant lies in between the observer & projection plane. Therefore the front view of point A will be in the vertic plane (V.P.) and the top view will be on the horizontal plane. Similarly, point B in the 3rd quadrant can be projected on the horizontal & vertical plane.

As shown in the above image, point A in the 1 quadrant lies in between the observer & projection plane. Therefore the front view of point A will be in the vertical plane (V.P.) and the top view will be on the horizontal plane. Similarly, point B in the 3 quadrants can be projected on the horizontal & vertical planes.

To understand why the 2 & 4 angles orthographic projection systems are not used to draw engineering drawings. We will repeat the above experiment of creating engineering drawing views in the second & fourth quadrant.
Let’s consider rectangular parts X & Y are placed in 2 & 4 quadrants respectively.

In the second quadrant, the vertical plane (VP) lies in between object X & observer. Therefore the front view of object X will lie on a vertical plane whereas the top view will lie on the horizontal plane. As per the rule of projection when the horizontal plane is rotated 90 degrees in the clockwise direction, the top & front views will overlap.

Overlapping projection views create confusion in the drawing. Therefore the 2 angle projection system is not used to draw engineering drawings. Similarly, when the object is placed in the 4 quadrants both the top & front views will overlap. Therefore fourth angle projection is also not used.

What is GD&T? What are the benefits of GD&T?

Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering tolerances.
It uses 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.

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 dimensions and feature control frames using a datum reference

Benefits of GD & T:
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.

Explain all the symbols used in GD&T?

Surface Straightness:

The standard form of straightness is a 2-Dimensional tolerance that is used to ensure that a part is a uniform across a surface or feature. Straightness can apply to either a flat feature such as the surface of a block, or it can apply to the surface of a cylinder along the axial direction. It is defined as the variance of the surface within a specified line on that surface.

Axis Straightness:

The form of straightness that controls the central axis of a part is sometimes referred to as Axial Straightness. This tolerance callout specifies how straight the axis of a part is (usually a cylinder). By definition, axis straightness is actually a 3D tolerance that constrains the center axis of the part preventing it from bending or twisting too far.

Flatness:

GD&T Flatness is very straight forward. It is a common symbol that references how flat a surface is regardless of any other datums or features. It comes in useful if a feature is to be defined on a drawing that needs to be uniformly flat without tightening any other dimensions on the drawing. The flatness tolerance references two parallel planes (parallel to the surface that it is called out on) that define a zone where the entire reference surface must lie. Flatness tolerance is always less than the dimensional tolerance associated with it.

circularity :

The circularity symbol is used to describe how close an object should be to a true circle. Sometimes called roundness, circularity is a 2-Dimensional tolerance that controls the overall form of a circle ensuring it is not too oblong, square, or out of round. Roundness is independent of any datum feature and only is always less than the diameter dimensional tolerance of the part. Circularity essentially makes a cross-section of a cylindrical or round feature and determines if the circle formed in that cross-section is round.

Cylindricity

The Cylindricity symbol is used to describe how close an object conforms to a true cylinder. Cylindricity is a 3-Dimensional tolerance that controls the overall form of a cylindrical feature to ensure that it is round enough and straight enough along its axis. Cylindricity is independent of any datum feature the tolerance needs to be less than the diameter dimensional tolerance of the part. Cylindricity essentially forms a perfect cylindrical boundary around the object that the entire 3-Dimensional part must lie in.

Perpendicularity:

Perpendicularity is a fairly common symbol that requires the referenced surface or line to be perpendicular or 90° from a datum surface or line. Perpendicularity can reference a 2D line, but more commonly it describes the orientation of one surface plane perpendicular to another datum plane. The tolerance of the perpendicularity callout indirectly controls the 90° angle between the parts by controlling the location where the surfaces have to lie. See the tolerance zone below for more details.

Note: Perpendicularity does not control the angle of the referenced feature –the tolerance is in distance units. (mm/in)

Angularity

Angularity is the symbol that describes the specific orientation of one feature to another at a referenced angle. It can reference a 2D line referenced to another 2D element, but more commonly it relates the orientation of one surface plane relative to another datum plane in a 3-Dimensional tolerance zone.

Parallelism

Parallelism is a fairly common symbol that describes a parallel orientation of one referenced feature to a datum surface or line. It can reference a 2D line referenced to another element, but more commonly it relates the orientation of one surface plane parallel to another datum plane in a 3-Dimensional tolerance zone. The tolerance indirectly controls the 0° angle between the parts by controlling where the surface can lie based on the datum. See the tolerance zone below for more details.

Note: Parallelism does not control the angle of the referenced feature, but only creates an envelope in which the feature must lie.

It is important to determine what the reference feature is (surface or axis) and then what is acting as the datum (surface or axis) to determine how the parallelism is to be controlled.

True Position

True Position is actually just referred to as Position in the ASME Standard. Many people refer to the symbol as “True” Position, although this would be slightly incorrect. The Position tolerance is the GD&T symbol and tolerance of location. The True Position is the exact coordinate, or location defined by basic dimensions or other means that represents the nominal value. In other words, the GD&T “Position” Tolerance is how far your feature’s location can vary from its “True Position”.

Profile of a surface

Profile of a surface describes a 3-Dimensional tolerance zone around a surface, usually which is an advanced curve or shape. If it is called out on a curved surface, like a fillet on a welded part, the entire surface where the radius is has to fall within the tolerance zone. Profile controls all the points along the surface within a tolerance range that directly mimics the designed profile. Any point on the surface would not be able to vary inside or outside by more than the surface profile tolerance. Usually, when surface profile is required, there are no tolerances on the dimensions that describe the surface and use the GD&T callout to give the acceptable range.

Profile of a line

Profile of a line describes a tolerance zone around any line in any feature, usually of a curved shape. Profile of a line is a 2-Dimensional tolerance range that can be applied to any linear tolerance. If it is called out on a surface, like a radius on a part – profile of a line would specify how much that cross-section could vary from a true curved radius. Profile of a line takes a cross section at any point along the surface and sets a tolerance zone on either side of the profile.

Total Runout

Total Runout is how much one entire feature or surface varies with respect to a datum when the part is rotated 360° around the datum axis. Total runout controls both the amount of variation in the surface as the part is rotated, but the amount of variation in the axial dimension. Both radial variation and axial variation are measured and held within the tolerance. Total Runout is usually called on a part that is rotated about an axis where the entire surface is critical to be in spec.

Runout

Runout is how much one given reference feature or features vary with respect to another datum when the part is rotated 360° around the datum axis. It is essentially a control of a circular feature, and how much variation it has with the rotational axis. Runout can be called out on any feature that is rotated about an axis. It is essentially how much “wobble” occurs in the one part feature when referenced to another.

Concentricity

Concentricity, (called coaxiality in the ISO Standard), is a tolerance that controls the central derived median points of the referenced feature, to a datum axis. Concentricity is a very complex feature because it relies on measurements from derived median points as opposed to a surface or feature’s axis.

Symmetry

GD&T Symmetry is a 3-Dimensional tolerance that is used to ensure that two features on a part are uniform across a datum plane. An established “true” central plane is established from the datum and for the symmetry to be in tolerance, the median distance between every point on the two surface features needs to fall near that central plane. Each set of points on the reference features would have a midpoint that is right between the two. If you take all the midpoints of the entire surface, this must lie within the tolerance zone to be in specification