Week 9:- 2D Detailing Challenge

1. What are the Drawing templates?

Answer:

First of all let we know about some basic definition of drawing.

Drawings (A graphical representation):

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 are basically the drawing standards as per customer’s specifications.
• Drawing templates are format that are used for detailing of different parts or units of the fixture.
• A drawing templatefile 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 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 of projection to be used, views to be considered, scaling of the drawing as per the part or unit.
• Separate template is prepared for each sheet size like A1, A2, A3, A4 & so on.

2. What do you understand by Angle of projection?

Answer:

Angles of Projection:

• The angleat which an observer draw an object to convert it from 3D to 2D plane such as real object image to a plane paper is known as 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 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

2. Pattern of planes & pattern of views.

3. Methods of drawing orthographic projections.

• There are two types of projection method majorly used in industry. First & third angles of projection are majorly used in automotive standards.

• Understanding the angles of projection helps us to derive the actual image of 2D drawing.
• It is also very important for various manufacturing processes for machine shop operators.
• Symbol used for first & third angles of projection are as belows.

3. What is the First angle & Third angle projection? and why can't we use the 2nd and 4th angle of projection?

Answer:

First angle of projection:

• In this, the object is assumed to be positioned in the first quadrant & is shown in 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 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 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.

• The basic difference between first & third angle of projection are as belows.

• Why 2nd & 4th angle projection is not used?

Second & fourth angle of projection systems are 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 1st & 3rd quadrant respectively. As per rule of orthographic projection, to bring drawing views from three dimensional to two dimensional planes. Horizontal plane (HP) is rotated in the clockwise direction.

 As shown in the above image, point A in the 1st quadrant lies in between the observer & projection plane. Therefore 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 3rd quadrant can be projected on the horizontal & vertical plane.

To understand why the 2nd & 4th angle orthographic projection system 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 2nd & 4th quadrant 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 vertical plane whereas top view will lie on horizontal plane. As per rule of projection when the horizontal plane is rotated 90 degree in clockwise direction, top & front view will overlap. Overlapping projection views create confusion in the drawing. Therefore the 2nd angle projection system is not used to draw engineering drawings. Similarly when the object is placed in the 4th quadrant both top & front view will overlap. Therefore fourth angle projection is also not used.

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 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 precisionis 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 dimensionsand feature control frames using a datum reference (both shown above).
• GD & T: Is a method (systems of symbols) for defining a part’s geometry

– it goes beyond the form description.

– based simply on tolerance dimensions.

A feature control frame (the backbone of GD & T) modifies a part’s geometry.

• Two additional examples of feature control frames modifying a part’s geometry.

• A datum is an exact surface, line, point, axis or cylinder from which measurements are taken.

-Ex. A surface plate or a polished slab of granite (simulated datum).

-3 points define a plane.

-Datum feature – is the surface of the part in contact with the simulated datum.

• A height gage measures the height of an object from the simulated datum surface of a surface plate.

• Degrees of freedom (12) allow movement in two directions along each axis and rotation about each axis (clockwise and counterclockwise).

• In order to measure geometric features. Part motion must be restricted. A datum reference frame consists of three intersecting planes at 90° to each other.

• The part can still move in the positive X, Y and Z directions “part motion must be restricted”.
• What if we temporarily clamped the part? → Measurements can be taken from the simulated datums.
• The datum symbol is applied to solid cylinders.

• The datum symbol is applied to holes.

• Order of datums : Primary datum S has 3 pts of contact, secondary datum T has 2 pts and tertiary datum U has 1pt of contact.

• There are several standards available worldwide that describe the symbols and define the rules used in GD&T. One such standard is American Society of Mechanical Engineers(ASME) Y14.5.

Benefits of GD & T:

a) 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.

c) 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.

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

e) 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.

5. Explain all the symbols used in GD&T?

Answer:

• Table below lists GD&T geometric characteristic symbol.

Form tolerance type:

• Flatness: GD&T Flatness is a common symbol that references how flat a surface is regardless of any other datum’s 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 drawing callout:

Flatness tolerance Zone:

Two Sets of Parallel Planes where the entire referenced surface must lie.

• Straightness: Straightness actually has two very different functions in GD&T depending on how it is called out. In its normal form or Surface Straightness, is a tolerance that controls the form of a line somewhere on the surfaceor the feature.  Axis Straightness is a tolerance that controls how much curve is allowed in the part’s axis. This is usually called out with an included call to maximum material condition. Both callouts are very different from each other!

Straightness Drawing callout:

Straightness Tolerance Zone:

Surface:

Two Parallel Lines on either side of a surface line where the surface must lie (2D).

Axis:

A cylindrical boundary around the true central axis of the part, where the derived midpoint axis of the part must fit into.

• 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 datumfeature 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.

Cylindricity Drawing callout:

Cylindricity Tolerance Zone:

• 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.

Drawing callout:

Tolerance Zone: Two concentric circles, one inner and one outer, in which all the points within the circular surface must fall into. The tolerance zone lies on a plane that is perpendicular to the central axis of the circular feature.

Orientation tolerance type

• Perpendicularity: Perpendicularity in GD&T can mean two very different things depending on which reference feature is called out. The normal form or Surface Perpendicularity is a tolerance that controls Perpendicularity between two 90° surfaces, or features. Surface Perpendicularity is controlled with two parallel planes acting as its tolerance zone. Axis Perpendicularity is a tolerance that controls how perpendicular a specific axis needs to be to a datum. Axis Perpendicularity is controlled by a cylinder around a theoretical perfectly parallel axis. Pay close attention if a hole or pin is referenced since axis perpendicularity is commonly called out on these features.

Drawing callout:

Tolerance Zone:

Surface: Two parallel planes or lines which are oriented perpendicular to the datum feature or surface. The planes are held perpendicular to the datum, but only ensure that the entire feature falls into the tolerance zone.

Axis: A cylinder surrounding a referenced theoretical axis which is directly perpendicular to the datum feature. The tolerance zone is the diameter of this symbol in which the central axis of the measured feature must lie.

• Parallelism: Parallelism actually has two different functions in GD&T depending which reference feature is called out. The normal form or Surface Parallelism is a tolerance that controls parallelism between two surfaces or features. The surface form is controlled similar to flatness with two parallel planes acting as its tolerance zone. Axis Parallelism is a tolerance that controls how parallel a specific parts central axis needs to be to a datum plane or axis. The axis form is controlled by a cylinder around a theoretical perfectly parallel axis. Parallelism is most commonly called out as surface parallelism. However, be sure to pay attention if it is referencing a central axis because it is different!

Drawing callout:

Tolerance Zone: Two parallel planes or lines which are oriented parallel to the datum feature or surface. All points that are on the referenced feature must in the tolerance zone.

• 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.  The tolerance does not directly control the angle variation and should not be confused with an angular dimension tolerance such as ± 5°.  In fact, the angle, for now, becomes a Basic Dimension, since it is controlled by your geometric tolerance. The tolerance indirectly controls the angle by controlling where the surface can lie based on the datum.

Drawing callout:

Tolerance Zone: Two parallel planes or lines which are oriented at the specified angle in relation to a datum. All points on the referenced surface must fall into this tolerance zone.

Location tolerance type:

• 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 features location can vary from its “True Position”.

Drawing callout:

Tolerance Zone: A 2-dimensional cylindrical zone or, more commonly a 3-Dimensional cylinder, centered at the true position location referenced by the datums.

The cylindrical tolerance zone would extend though the thickness of the part if this is a hole. For the 3-dimensional tolerance zone existing in a hole, the entire hole’s axis would need to be located within this cylinder.

• Concentricity: Concentricity, sometimes called coaxially, is a tolerance that controls the central axis of the referenced feature, to a datum axis. The axes for the datum and referenced feature are derived from the median points of the part or feature. Concentricity is a very complex feature because it relies on measurements from a derived axis as opposed to tangible surface or feature.

Drawing callout:

Tolerance Zone: 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.

• 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.   Symmetry is not a very common GD&T callout since it has very limited functional uses (centering location is done with Position) and the verification and measurement of symmetry can be difficult.

Drawing callout:

Tolerance Zone: Parallel Planes on equal sides of a central datum plane. The median points of the symmetrical surfaces must all lie within this zone.

Profile tolerance type

• 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.

Drawing callout:

Tolerance Zone: 3-Dimensional tolerance zone existing of 2 parallel surface curves that follow the contour of the surface profile across the entire length of the surface. This tolerance zone may or may not be referenced by a datum.

• 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. The profile of a line callout can also be set with an all-around leader or given a specific range.

Drawing callout:

Tolerance Zone: 2-Dimensional tolerance zone existing of two parallel curves that follow the contour of the true surface profile. The application on where the tolerance zone applies can be specified on the drawing. This tolerance zone may or may not be referenced by a datum.

Runout tolerance type:

• Circular 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.

Drawing callout:

Tolerance Zone: 2-Dimensional circular tolerance zone that is defined by a datum axis where all points on the called surface must fall into. The zone is a direct reference to the datum feature. Runout is the total variation that the reference surface can have when the part is rotated around the datum’s true axis.

• 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.

Drawing callout:

Tolerance Zone: A 3-Dimensional cylindrical tolerance zone that surrounding a referenced surface that is directly derived from either the datum surface or the axis. All points along the surface must fall within this zone when the part is rotated at all times.

• Table lists GD&T geometric characteristic symbol modifiers.

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