1: Sketching
- Page ID
- 113021
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)What is sketching
A sketch is a 2D representation of your part or design, typically drawn by hand on engineering paper. This allows engineers to prototype their parts in a low-stakes environment before committing to using CAD and further prototyping their design. Sketches use standard views and lines which are used throughout different engineering disciplines and applications to convey information effectively. More information about various views and lines is available below.
Views
Two standard views are typically used when sketching or viewing a finished part: isometric and orthographic.
Orthographic
Orthographic views are helpful when sketching largely planar objects. They provide a direct view along the X, Y, or Z axis, displaying only two dimensions at a time. Orthographic sketches often include multiple views (e.g., front, side, and top) to convey all necessary details, using different line types to represent features. Orthographic views let you represent 3D geometry in a 2D view.
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When creating orthographic sketches, align the front, side, and top views on the sketch paper to maintain consistency.
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Engineering sketch paper typically includes a grid with small dashed sections, often spaced 5 mm apart, which helps with alignment. However, grid spacing may vary depending on your chosen scale.
Figure 1.) An orthographic technical sketch of the Gameboy handheld console. The principal view (1) is what all other views are projected off of. The projected views (2, 3, 4, 5, 6) are derived from the principal view and display various back, side, and top views. A good set of orthogonal views can show all the parts' geometry.
Isometric
Isometric views are effective for representing complex geometry in a single view. These views are angled such that the X, Y, and Z axes appear 60 degrees apart, allowing all three dimensions to be seen in one sketch. While this view is beneficial for conveying complex shapes, it can be challenging to depict tapered or intricate geometry accurately be hand.
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When sketching in isometric views, track each axis closely and ensure proper dimensioning to maintain accuracy.
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Similar to orthographic views, isometric sketch paper includes dashed grid sections that assist in part alignment. With all three dimensions visible, it is essential to monitor them carefully.
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Many students find it helpful to sketch key points before connecting them with lines, particularly for complex shapes like cones.
Figure 2.) An example of a complete isometric view of a Game Boy handheld console.
Title Block
Each sheet of engineering sketch paper includes a title block, which helps organize and track sketches.
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The title block allows you to set the drawing scale. For example, a scale of 1:1 indicates that the sketch is the actual size, while a scale of 2:1 means the drawing is twice the actual size of the part. A 1:2 scale represents the part at half its actual size. Defining the scale at the start helps maintain accuracy throughout the sketch.
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You can also record the part's title and creator in the title block, which provides a space for another engineer to approve the part for later review. This ensures accountability and keeps track of who worked on each part, making the title block an integral component of engineering documentation.
Figure 3.) An example of a title block in the process of being filled out.
Lines
Proper dimensioning is essential for accuracy in part sketches. The following line types and conventions are used to assist with this process.
Visible Lines
Solid lines represent the visible edges and contours of a part. Use them only for surfaces that are directly observable.
Figure 4.) Visible lines representing a wall of a box broken by a rounded surface. Tangent edges are set to visible to show the transition to a rounded surface. This feature can be enabled and disabled in most software.
Hidden Lines
Hidden lines are dashed and indicate geometry obscured by other features, such as holes or interior shapes. They are especially useful for complex geometry and often define radii or hidden components. Hidden lines are typically about ⅛ inch long with a 1/32 inch gap between dashes.
Figure 5.) An example of a set of hidden lines next to visible lines. These hidden lines represent an indentation into a part's wall.
Dimension Lines
Dimension lines provide measurements for the sketch. By convention, they should not touch the part directly but should be close enough to avoid misinterpretation. Place dimensions on the most appropriate view, as it may vary from other dimensions of the feature.
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Place the exact dimension on the line if space allows, or near the end of the line if space is limited.
Figure 6.) An example of Dimension Lines applied to a square assembly. Dimension lines can represent rounded surfaces, angles, and linear dimensions.
You can dimension to hidden lines, especially when the hidden feature is visible in another view. This practice helps clarify radii and hidden features that might otherwise be difficult to identify.
Center Mark
When defining a radius, use a center mark—a small cross at the center of a full or partial circle—to pinpoint the exact center. Dimension lines can extend from this mark to further specify the center’s location.
Figure 7.) An example of Center Marks applied to two concentric circles.
Break Lines
Break lines are used when parts are too long to fit on engineering paper at the chosen scale. These lines can reflect the material’s properties, such as a jagged break for wood. Dimension lines can cross a break line to measure long components. Using break lines can simplify the drafting process for longer parts, but their application is up to the drafter’s discretion.
Figure 8.) An example of Break Lines is used to shorten a drawing of a very long part.