Technical Drawing Types and Purpose

Technical Drawing Forms

• Concept/idea sketch is also referred to as a napkin sketch
• Computation sketch involves a computer
• Design sketch is more detailed and follows a concept
• Layout drawing is often referred to as a "Map"
• Part drawing shows each component
• Working/construction drawing is an instruction on how to build and maintain.
• Electrical drawing shows the layout of electrical components
• Installation Drawing details how to install each component into project
• Assembly drawing shows how to assemble each component/overall project

Purposes of Technical Drawing

• Visualization
• Communication
• Documentation

Descriptive Geometry

• Descriptive geometry projects 3D figures onto a 2D paper

Documentation Drawings

• Consists of physical/digital drawings that describe form, manufacture, assembly, maintenance and are considered legal documents

Roles

• Engineers apply science and math to solve problems
• Scientists/researchers develop laws and principles
• Technologists design applications
• Technicians supervise craftspeople and the workplace
• Craftspeople build things according to engineer specifications

Critical Soft Skills

• Meticulous documentation methods
• Effective communication, both written and verbal
• Conducting efficient meetings
• Insightful requirement gathering
• Productive interpersonal skills

Project Definition

• A project is a temporary endeavor to create a unique product, service, or result

Triple Point Constraints

• Every project needs to operate within the boundaries of scope, time, and cost
• Balancing these three elements is essential for maintaining quality, but only two are typically feasible

Design Cycle

• Sequence is concept (come up with idea), development (design), execution (build), transfer (pass over for maintenance long term)

Design Process

• Designing is creating a product or system to satisfy a set of requirements
• Multiple solutions are available by using available resources

Design Phases

• Identification
• Preliminary ideas
• Refinement
• Analysis
• Decision
• Implementation

Freehand Sketches

• Goal for freehand sketches are clarity, conciseness, and readability
• Freehand sketches should be signed, dated, and archived appropriately

Lines in Sketches

• Start with construction lines
• Thick lines should be twice the width of thin lines
• Centerlines and hidden lines are thinner than visible lines
• Bounding boxes are used for shapes like circles
• Triangles can be used to draw parallel lines

Line Styles

• Visible lines show visible edges and contours
• Hidden lines show hidden edges and contours
• Center lines represent axes or center planes of symmetrical parts/features and bolt circles/paths of motion
• Phantom lines show alternative positions of moving parts
• Cutting-plane lines define the location of cutting planes for section views, with ends at 90 degrees and arrowheads indicating viewing direction
• Section lining indicates cut surfaces in section views; break lines used when complete views aren't needed
• Dimension lines indicate extent/direction of a dimension, terminated with uniform arrowheads
• Extension lines with dimension lines point to the drawing where dimension applies
• Leader lines direct notes, dimensions, symbols, and part numbers on a drawing and are straight, inclined, except for a short horizontal part extending to the note
• Arrowheads terminate dimension, leader, and cutting-plane lines and have a length to width ratio of about 3:1

Sheet Sizes

• Most lettering on drawings should be 3mm tall
• Scale 1:2 represents half; 2:1 represents double

Projection Types

• Perspective projection, where projectors form a cone and resemble a photograph
• Parallel projection, where all object features are parallel projections avoiding overlap
• Orthographic Projections are parallel, perpendicular to projection plane (often tilted 45 degrees), and show true size/scale
• Multiview projection splits a 3D object into views for better understanding

Multiview Projection

• An object in a glass box reveals six views, but only three are needed.
• First angle projection places the object onto a 2D space.
• Third angle projection projects the 2D drawing onto a 3D space
• Parallel hidden lines should be staggered

Lecture 5

• Isometric positions have angles all equal to 120 degrees

Lecture 6

• Oblique projections use parallel projectors at angles other than 90 degrees to the projection plane, showing true size/shape of one principal face
• Miter lines: Used to transfer depth information between related views.

Oblique Projection Types

• Cavalier: Angle of 45°, receding axis scale of 1
• Cabinet: Angle of 63.43°, receding axis scale of 1/2
• General: Angle between 45° and 63.43°, receding axis scale between 1/2 and 1
• Projection plane should be parallel to the principal face containing the most complex/irregular shape
• Use longest shape as front

Auxiliary Views

• Auxiliary views provide information for when the orthographic views are confusing or ambiguous.
• An auxiliary view is an orthographic view projected onto any plane other than the principle planes
• Partial auxiliary views show features of a specific face projected onto a slant/curve
• Do not include hidden lines

Sectional Views

• Sectional views remove material to show internal features better, reducing hidden lines and improving dimensional clarity
• A cutting plane is where an object is cut in half, typically parallel to orthogonal planes
• No hidden lines should be shown in sectional views

Hatching Lines

• Should not be parallel or perpendicular to visible lines and should be thinner and lighter
• Hatching lines requires use of different styles to distinguish separate components for multiple objects
• Omission of visible lines within a sectional view is required for the hatching lines

Types of Sections

• Half section exposes half of an object, used typically for symmetrical and cylindrical objects.
• Revolved section rotates a thin slice by 90 degrees, used normally for cross sections of beams.
• Removed section: Separates the revolved section from the entire object

Hatching Conventions

• Do not hatch features including ribs, webs, lugs, and spokes
• Parts in assembly drawings are unhatched and include fasteners, gaskets, gears, springs, bearings, and axles

Break Lines

• Utilized to shorten an object with consistent cross section to allow it to fit on the page

Offset Section

• An offset section occurs if the cutting plane isn't parallel to a face but cuts apart parts of an object to show more detail.

Dimension Line

• Centerlines are usable as extension lines for circular features

Dimension Values

• Unidirectional dimension values are oriented horizontally, relative to the page
• Aligned: dimension values are oriented parallel to the associated dimension line

Notes on Dimensions

• Consistency should be kept within a drawing
• Dimension lines should be placed outside the object
• Extension lines can cross other extension lines and visible lines
• Dimension lines cannot cross extension lines or other dimension lines
• Dimension visible lines over hidden lines are best

Baseline

• Baseline is easier to read

Right Angles

• Intersection of visible lines (T-joints) should not be dimensioned

Angles

• Angles should be dimensioned from the bottom of the face to the top

Dimension Values Standards

• Shown using metric or decimal inch values
• Mention located in title block

Units of Measurement

• Millimeters/meters are indicated with "mm" or "m"
• Inches/feet are indicated with “ or ‘ (5'11) or (11")

Curves

• For curves, holes are dimensioned where they appear as circles
• Cylinders indicated in area they appear as rectangles
• Curved features have dimensions derived by radius and height to teh center of the curve

Repeated Features

• Repeated features show as TYP, or “Number x”
• “Typ” is placed After
• “Number x” is placed Before PL (place) can be used instead of “x”

Depths Indication

• The arrow pointing down represents how deep a hole is
• All the way through is marked as THRU

Additional Indicators

• .531 THRU ALL
• 1.125.364, representing a counter bore.
• .500 1.000 represents the first value through
• .531 THRU ALL 1.017 X 100° a countersink measurement

Coordinate Dimensioning

• Coordinate dimensioning can allow for identification of a corner of the part as 0,0 location, with each feature having its own set of x and y dimension

Hole Tables

• Indicate different hole dimensions and are labelled in the drawing with letters
• Usually used with coordinate dimension
• SIZE SYMBOL, HOLE Ø, A, B, C, D show values of dimensions and labels

Notes

• Notes can be attached to drawings using leaders
• Leaders are often attached to the front of the first word
• Placement of notes happens after dimensioning is complete.

Note Restrictions

• Notes should not touch lines of drawing or title block

Tolerance

• Tolerance indicates the level of permissible error associated with the creation of an object
• Defined via maximum and minimum size limits

Tolerance Cost

• Higher tolerance means less error but higher cost

Sizes

• Nominal size indicates the desired size
• Actual size indicates the actual produced size

Tolerance Denotation

• Can be shown as +- or as a value
• Double the value of the +- value to account for the maximum and minimum limit of size
• (Example, 3.25 +- 0.03 has tolerance of 0.06 - 0.03 over and 0.03 under)

Tolerance Types

• Unilateral is the first
• Bilateral is the second,
• General tolerances can be marked can put in the title block

Limit Tolerances

• The tolerance value is directly applied to the dimension
• In chain dimensioning, tolerance is additive
  • Tolerance accumulates
• In baseline dimensioning, all dimensions are specified from the same point
• In direct dimensioning, you can indicate tolerance directly connecting the features

Graphic Excellence

• Should be a well-designed presentation of interesting data (substance, statistics, design), needs to be clear, precise, and efficient
• Time-series displays work best for big data sets with real variability
• A graph does not distort if the visual representation of the data is consistent with the numerical representation

Lie Factor

• Lie factor indicates the amount of distortion in a graph
• Calculated via size of the effect shown in the graph/ size of effect show in data
• Lie factor > 1 means the graph is lying
• The representation of numbers as physically measured should be directly proportional to the numerical quantities represented
• The most frequently printed graphic is display of government spending and debt over the years
• Avoid use of higher dimensions to show one-dimensional data (3d graph)
• Context is essential for graphical integrity: it must exhibit truth, revealing and the graphics must bear the question: “compared to what?"
• Less data should always provoke suspicion for lies

Graphical Integrity Principles include

• 1. The representation of numbers, as physically measured on the surface of the graphic itself, should be directly proportional to the numerical quantities represented.
• 2. Clear, detailed, and thorough labeling should be used to defeat graphical distortion and ambiguity. Write out explanations of the data on the graphic itself. Label important events in the data.
• 3. Show data variation, not design variation.
• 4. In time-series displays of money, deflated and standardized units of monetary measurement are nearly always better than nominal units.
• 5. The number of information-carrying (variable) dimensions depicted should not exceed the number of dimensions in the data.
• 6. Graphics must not quote data out of context

Data Graphics

• Should draw the users attention to the data itself
• Data density of graphic defined as number of entries/ area of graphic
• Our eyes can make a remarkable number of distinctions within a small area
• With the use of very light grid lines, it is easy to locate 625 points in one square inch
• Majority, if not all of the ink should be used to present data-information

Ratio Details

• Data-ink ratio defined as data ink/total ink used to print the graphic
• Redundant data-ink depicts the same number over and over

Chart Junk

• Chartjunk refers to the interior decoration of graphics that adds new value to a design
• Avoid use of moire shading

DUCK

• If a graphic is taken over by excessive decorative elements, it becomes a DUCK

Fonts

• Sans Serif font is best for presentations
• Using all capitals has limited readability compared to lowercase
• Implement on light backgrounds with dark text or dark background with light text
• Red-green, blue-yellow color palettes

Layout Style

• Keep text blocks, such as headlines and listed items, to no more than two lines
• Keep lists to two, three, or four items; make listed items parallel; avoid sublists if possible
• Use generous white space

Presentation Notes

• Limit the number of items on each slide
• Limit the number of slides so that you can dedicate at least one minute to each
• "SO WHAT” is an important aspect to consider for a presentation
• Challenger air craft exploded due to a lack of visual communication