Week 9:- 2D Detailing Challenge

Q-1 WHAT ARE THE DRAWING TEMPLATES?

• DRAWING ( AGRAPHICAL REPRESENTATIO):
• 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:

1. Drawing templates are the drawing standards as per customer’s specifications.
2. Drawing templates are format that are used for detailing of different parts or units of the fixture.
3. A drawing template file is a drawing file that has been saved with a .dwt file extension, and it specifies the styles, setting, and layouts in a drawing, including title blocks.
4. There are ‘n’ numbers of details that are available on the template and are useful for various manufacturing processes, such as, machining finish, tolerance, surface treatments, material, name of the parts, name of the assemblies etc.
5. Preparing a drawing template at the start of the project can help us save time, as these can be used a start model for detailing for different parts.
6. 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.

Q-2 WHAT DO YOU UNDERSTAND BY ANGLE OF PROJECTION?

• Angles of projection:

1. The angle at 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.
2. Angles of projection are basically the view formats for orthogonal views of assemblies or parts.
3. Orthogonal projection: It is a technical drawing in which different views of an object are projected on different reference planes observing perpendicular to respective preference plane.
4. Different reference planes are horizontal plane (HP), vertical frontal plane (VP), side or profile plane.
5. 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 orthogonal projections:

1. Plane

2. Pattern of planes & patterns of views

3. Methods of drawing orthographic projection

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

• Understanding the angle of projection helps us to drive 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 below.

Q-3 WHAT IS THE FIRST ANGLE & THIRD ANGLE PROJECTION? AND WHY CAN’T WE USE THE 2^ND AND 4^TH ANGLE OF PROJECTION?

• 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 view are obtained by projecting the images on the respective plane.
• 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 fro various points of the object to meet the projection plane. When these meeting points are joined in order on the plane they from an image, thus in the first angle projection, any view is so placed that it represents the sied 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 plne & 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 of projection is assumed to be transparent. The intersection of this plane with the projectors from all the points of the object would from an image on the transparent plane.
• The basic difference between first and third angle of projection are as below.

• Why 2^nd and 4^th angle projection is not used?
• Second & forth angle of projection system 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 1^st & 3^rd 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 1^st quadrant lies in between the observer & projection plane. Therefore front view of point A will be in the vertical plane and the top vies will be on the horizontal plane. Similarly point B in the 3^rd quadrant can be projected on the horizontal & vertical plane.
• To understand why the 2^nd and 4^th 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 and forth quadrant.
• Let’s consider rectangular parts X & Y placed in 2^nd & 4^th quadrant respectively.
• In the second quadrant, the vertical plane lies in between object X & observer. Therefore the front view of the object X will lie on vertical plane where as plane is rotated 90 degree in clockwise direction, top & front view will overlap. Overlapping projection views create confusion in the drawing. Therefore the 2^nd angle projection system is not used to draw engineering drawings. Similarly when the object is placed in the 4^th quadrant both top & front view will overlap. Therefore fourth angle projection is also not used.

Q-4 WHAT IS GD&T? WHAT ARE THE BENEFITS OF GD&T?

• Geometric Dimensioning and Tolerance (GD&T) is a system for defining and communicating engineering tolerance.
• 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 machined what degree of accuracy and precisions needed on each controlled feature of the part.
• GD&T is used to define the nominal 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-molded or as-intended geometry. One example is a basic dimension. Tolerancing specifications define the allowable variation and location between features. Two example are linear dimensions and feature control frames using a datum reference.
• GD&T is a method (systems of symbols) for defining a parts geometry.
• It goes beyond the from description.
• Based simply on tolerance dimensions.
• A feature control frame modifies a parts geometry.

• Two additional examples of feature control frames modifying a parts geometry.

• A datum is an exact surface, line, points, axis or cylinder from which measurements are taken.
• A surface plate or a polished slab granite.
• 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.

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

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

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

• The datum symbol is applied to holes.

• Order of datum : 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 world wide 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:

1. Saving money – GD&T enhances design accuracy by allowing for appropriate tolerances that maximize production. For many projects, the process provides extra or bonus tolerance, further increasing cost effectiveness.
2. Ensuring dimensional and tolerance requirements – By explicitly stating all design requirements, a through GD&T process guarantees accurate fulfillment of all dimensional and tolerance specifications.
3. 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.
4. Offering uniformity and convenience – As a single, consistent language, GD&T reduces guesswork and interpretation while ensuring consistent geometries across design and manufacturing.
5. Providing accurate communication – Today’s intricate design demand the most accurate and reliable communication. GD&T enables designers, manufactures, and inspectors to communicate clearly with one other, saving time and making the process more efficient.

Q-5 EXPLAIN ALL THE SYMBOLS USED IN GD&T?

• 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 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 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 hoe it is called out. In its normal form or surface straightness, is a tolerance that controls out. In its normal form of a line somewhere on the surface or the feature. Axis straightness is a tolerance that controls how much curve is allowed in the parts axis. This is usually called out with a n 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 wither 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 described how close an object conforms to a true cylinder. Cylindricity is a 3D 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 essensially forms a perfect cylindrical boundary around the object that the entire 3D 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 2D 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.
• Circularity drawing callout:

• Circularity 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 on which reference feature is called out. The normal form or surface Perpendicularity is a tolerance that controls Perpendicularity between two 90^o 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 a datum. Axis Perpendicularity is controlled by a cylindrical 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.
• Perpendicularity drawing callout:

Surface perpendicularity

Axis perpendicularity

• 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 cylindrical 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 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 referring a central axis because it is different.
• Parallelism Drawing zone:

• Parallelism 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 plan in a 3D tolerance zone. The tolerance does not directly control the angle variation and should not be confused with an angular dimension tolerance such as ‑⁺ 5⁰ . 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.
• Angularity Drawing callout:

• Angularity 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”.
• Position drawing callout:

• Position tolerance callout: - A 2D dimensional cylindrical zone or, more commonly a 3D cylinder, centered at the true position location referenced by the datum.
• The cylindrical tolerance zone would extend though the thickness of the part is this is a hoel. For the 3D 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 feature to a datum axis. The axis 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 or feature.
• Concentricity drawing callout:

• Concentricity tolerance zone: - Concentricity is a 3D cylindrical tolerance zone that is defined by a datum axis where all the derived median points of the reference surface cross sections from the theoretical axis that must be in this tolerance zone.

• Symmetry:
• GD&T symmetry is a 3D tolerance that is used to ensure that two feature 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 n specification. Symmetry is not a very common GD&T callout since it has very limited functional uses and the verification and measurement of symmetry can be difficult.
• Symmetry drawing callout:

• Symmetry 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 describe a 3D 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 tolerance on the dimensions that describe the surface and use the GD&T callout to give the acceptable range.
• Profile of a surface drawing callout:

• Profile of a surface tolerance zone: - 3D 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 described a tolerance zone around any line in any feature, usually of a curved shape. Profile of a line in a 2D 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 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.
• Profile of a line drawing callout:

• Profile of a line tolerance zone: - 2D tolerance zone existing of a 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 re referenced by s 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 360⁰ around the datum axis. It is essential 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.
• Circular runout drawing callout:

• Circular runout tolerance zone: - 2D circular tolerance zone that is defined by a datum axis 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 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 360⁰ around the datum axis. Total runout controls both 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 specification.
• Total runout drawing zone:

• Total runout tolerance zone: - A 3D 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.