how to do technical drawings

8/11/2019 How to Do Technical Drawings

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Lesson

How drawings are made

Technical drawings can be created in a variety of ways.

sketching (free hand drawing) using drafting instruments using CAD or other computer based tools

Figure Technical Drawing Sketched

Figure Technical Drawing using Drafting Instruments


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Figure Technical Drawing using CAD

Go to page b Reading a Drawing?Lines

Reading a drawing

Regardless of method, technical drawings are immediately recognizable by the types of lines,how they are drawn, and the organization of the content

Reading lines

Lines are the basic building blocks of a technical drawing. They are identified by particularcharacteristics as well as where and how they are used in a drawing. Generally called thealphabet of lines, the list includes

Construction Lines . Construction lines are used to block out the parts of a drawing.They are used in sketching (free-hand drawing) and drafting (using drawing instruments).Construction lines are drawn over or are erased. For that reason they are usually drawnvery lightly so that the pencil leaves no indents in the paper.


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Figure Construction Lines

Visible Object Lines . Visible object lines show the visible edges of objects. They aresharp, clear, and clean lines that will be part of the final drawing. Note that theconstruction lines are still in the drawing below.

Figure Visible Object Lines

Centreline . Centrelines are dashed lines with alternating short and long dashes. They areused to indicate the centre of an object that is symmetrical. They are sharp, clear, andclean lines that will be part of the final drawing. They are usually used to show where


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the centre of a feature is located e.g., the centre of a circle. They are often used inconjunction with measurements. When centrelines meet, they cross on the short dashes.

Figure Centre Lines

Hidden Object Lines . Hidden object lines are dashed lines that show where the edges ofobjects would be if you could see them - i.e. if they were not obscured by another part ofthe object. They are sharp, clear, and clean lines that will be part of the finaldrawing. The spaces are usually 1/3 as long as the dashes. When 2 hidden object linesmeet, they always meet with 2 dashes. If 2 hidden lines cross, the intersection is centredon the dashes.

Figure Hidden Object Line

Extension Lines . Extension lines are used to visually extend an edge or side so thatmeasurements may be included on the drawing. They are sharp, clear, and clean linesthat will be part of the final drawing. An extension line does not physically touch the

edges of the object, but is drawn close enough so that it is obvious which edge it isassociated with.


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Figure Extension Lines

Dimension Lines . Dimension lines are used to indicate measurements on adrawing. They are sharp, clear, and clean lines that will be part of the finaldrawing. Dimension lines usually end in arrow heads that touch the extensionlines. They may be broken to allow room for the measurements, as shown below.

Figure Dimension Lines

Dimension lines can take any of the following forms. Only one method would be used on adrawing. Methods are never mixed.


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Figure Aligned Dimensions

Figure Unidirectional Dimensions

Go to page c Reading a Drawing?Perspective

Reading perspective drawings

While perspective drawings are rarely used as technical drawings, it is important to know therelationship between perspective and technical drawings. Perspective drawings show the objectin 3 dimensional form. Just like in real life, or in a photograph, objects in perspective drawingsappear to get smaller as they get further away. The techniques for creating perspective drawingsfollow a number of straight forward principles. The drawings can get complex very quickly, andare time consuming to draw. The examples below show how a simple box appears in one-point,two-point, and three-point perspective.


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Figure One-point Perspective

Oblique drawings are similar to two-point perspective drawn below the horizon line, but do notuse vanishing points.

Figure Two-point Perspective

Isometric drawings are similar to two-point perspective drawn below the horizon line, but do notuse vanishing points.

Figure Three-point Perspective


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There is no technical drawing that approximates three-point perspective.

Go to page d Reading Drawings?Oblique

Reading Oblique Drawings

Oblique drawings are a form of technical drawing called pictorials that show the object as a 3-dimensional presentation. It shows the front of the object in plane view. The depth of the objectis shown by projecting the sides at a fixed angle. The projected are always parallel to each other.The back edges are parallel to the front edges.

Figure Oblique Projection

There are two types of oblique drawings

cabinet projection , which can have the sides angled at 45 0 or 60 0. The front is drawnfull scale, and the sides are drawn at 1/2 scale.

cavalier projection , which has sides angled at 300. The front and sides are drawn full

scale.

Figure Cabinet Projection (45 0 and 60 0)

Both boxes have the same dimensions. Front dimensions are shown to scale. Projectiondimensions (depth) are shown 1/2 scale.


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Figure Cavalier Projection

All dimensions are shown full scale. This is the same size box as shown in the cabinet projections.

Oblique drawings are used instead of one-point perspective because they are easier to draw, and

also take far less time to draw. The figure below shows a typical application of a cabinet projection.

Figure Cabinet Projection

Oblique has been mostly unused in recent years. Instead, isometric drawings are favoured.

Go to Part e Reading a Drawing?Isometric

Reading Isometric Drawings

Isometric drawings are another form of pictorial technical drawing. They are used instead oftwo-point perspective, but are much easier to draw. A rectangular box is drawn in isometricform with all edges either vertical, or at 30 degrees to the horizontal, as in the figure below.


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Figure Isometric Drawing

The faces of an object in an isometric drawing are labelled by their location.

Figure Faces of an Isometric Box

The labels are independent of the object that is drawn, or of the parts of the object.

Figure Isometric Views


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In this figure, the object is an upside down truck. The front view is actually the side of the truck,the top view is the bottom of the truck, and the right side view is the front of thetruck. Remember, the labels refer to the position in the drawing and have nothing to do withwhat the drawing is about.

Isometric techniques can be used to reproduce quite complex objects. A few examples areshown below

Figure Isometric Block With Cut-outs

Figure Isometric Blocks and Cylinders


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Figure Isometric Gears

Go to Part f Reading a Drawing?Orthographic Projections

Reading Orthographic Projections

Orthographic projections are projections of an isometric view onto a surface. It should not besurprising then, to learn that the standard orthographic projections are Front View, Right SideView, and Top View. Additional projections may be drawn for complicated isometricdrawings. Floor plans for houses and other buildings are nothing more than specially modifiedtop views.

The drawing below illustrates the relationship between an isometric drawing and an orthographic projection.

Figure Isometric?Orthographic Relationship

A simple way to to understand the relationship between isometric and orthographic is to cut aparta rectangular box (cardboard, for example) and lay it flat. The next drawings illustrate whathappens.


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Figure Isometric Box cut and folded flat

Figure Isometric Box with all faces separated


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Figure Orthographic Projections

In this figure, the left side, bottom, and back faces have been removed. The top, front and sidehave been relabelled as Top View, Front View, and Right Side View. Normally these are theonly views needed to give enough information to construct the object.

The orthographic drawings below illustrate typical applications of orthographics.

Figure Toolbox without handle


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Figure Cutting Board made from laminated strips

Further Information

Check the following site

Introduction to 3 Dimensional Graphics

Activity

Assigned activities

The purpose of these activities is to develop understanding of how technical drawings aremade. The activities will give you a feel for the techniques and will help develop yourcapabilities with sketching and using Corel Draw. All sketches should be done freehand?yes thatmeans no rulers. With a little practice, you can sketch a drawing in a few seconds. Using toolsfor the same thing can require hours of work. And, using rulers would be defeat the purpose ofthe exercise. You may wish to practice the drawings a few times to improve your sketchingskills.

Technical Drawings using Sketching

Sketch each of the following drawings using the supplied grid paper. Look at the videoclip if you need assistance. There are two sizes. The smaller one is 400 by 300 and willload faster than the larger 640 by 480 size.

o The sketches shown in the videos in this activity are all done with an HB drafting pencil in order for them to show up well in video.
http://www.ider.herts.ac.uk/school/courseware/graphics/3d_graphics.htmlhttp://www.ider.herts.ac.uk/school/courseware/graphics/3d_graphics.htmlhttp://www.ider.herts.ac.uk/school/courseware/graphics/3d_graphics.html


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o Normally this would be done with a 2H-3H pencil and, if necessary, darkenedwith an H pencil.

2MB

5MB

Oblique drawing

Print the Oblique Cabinet Projection Grid Using a sharp pencil, sketch the object below directly on the grid.

Figure Oblique Cabinet Projection

The completed sketch should look similar to this one

2MB

5MB

Isometric drawing

Print the Isometric Grid Using a sharp pencil, sketch the isometric drawing shown below directly on the

grid.
https://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/obliquecabinetgrid.pdfhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/obliquecabinetgrid.pdfhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/obliquecabinetgrid.pdfhttps://www.cdli.ca/learning-resources/technology-and-skilled-trades/ctecx104/unit-02/org03-ilo02/4-activity-a01.htmlhttps://www.cdli.ca/learning-resources/technology-and-skilled-trades/ctecx104/unit-02/org03-ilo02/4-activity-a01.htmlhttps://www.cdli.ca/learning-resources/technology-and-skilled-trades/ctecx104/unit-02/org03-ilo02/4-activity-a01.htmlhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/isogrid.pdfhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/isogrid.pdfhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/isogrid.pdfhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act02.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act02a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act01.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act01a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act02.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act02a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act01.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act01a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act02.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act02a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act01.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act01a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act02.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act02a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act01.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act01a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act02.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act02a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act01.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act01a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act02.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act02a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act01.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act01a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/isogrid.pdfhttps://www.cdli.ca/learning-resources/technology-and-skilled-trades/ctecx104/unit-02/org03-ilo02/4-activity-a01.htmlhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/obliquecabinetgrid.pdf


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Figure Isometric Drawing


3MB

8MB

Orthographic drawing

Print the Orthographic Grid Using a sharp pencil, sketch the orthographic drawing shown below directly on

the grid.

Figure Orthographic Drawing


5.5MB

13MB

Combined orthographic and isometric drawing

Print the Orthographic/Isometric Grid Using a sharp pencil, sketch the both the orthographic and isometric drawings

shown below directly on the grid.
https://www.cdli.ca/learning-resources/technology-and-skilled-trades/ctecx104/unit-02/org03-ilo02/4-activity-a02.htmlhttps://www.cdli.ca/learning-resources/technology-and-skilled-trades/ctecx104/unit-02/org03-ilo02/4-activity-a02.htmlhttps://www.cdli.ca/learning-resources/technology-and-skilled-trades/ctecx104/unit-02/org03-ilo02/4-activity-a02.htmlhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/orthographicgrid.pdfhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/orthographicgrid.pdfhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/orthographicgrid.pdfhttps://www.cdli.ca/learning-resources/technology-and-skilled-trades/ctecx104/unit-02/org03-ilo02/4-activity-a03.htmlhttps://www.cdli.ca/learning-resources/technology-and-skilled-trades/ctecx104/unit-02/org03-ilo02/4-activity-a03.htmlhttps://www.cdli.ca/learning-resources/technology-and-skilled-trades/ctecx104/unit-02/org03-ilo02/4-activity-a03.htmlhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/orthoisogrid.pdfhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/orthoisogrid.pdfhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/orthoisogrid.pdfhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act04.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act04a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act03.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act03a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act04.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act04a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act03.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act03a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act04.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act04a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act03.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act03a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act04.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act04a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act03.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act03a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act04.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act04a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act03.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/u2s3l3-act03a.avihttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/orthoisogrid.pdfhttps://www.cdli.ca/learning-resources/technology-and-skilled-trades/ctecx104/unit-02/org03-ilo02/4-activity-a03.htmlhttps://www.cdli.ca/resources/images/courses/ctecx104/unit02_org03_ilo02/orthographicgrid.pdfhttps://www.cdli.ca/learning-resources/technology-and-skilled-trades/ctecx104/unit-02/org03-ilo02/4-activity-a02.html


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Figure Orthographic and Isometric Drawings


For each type of drawing, scan your best sketch. Create a suitable entry in your course portfolio to include all your scans.

Publish your portfolio to your course portfolio web site

Test Yourself

There is no self test for this lesson.

Copyright 2012 All rights reserved. Centre for Distance Learning and Innovation.
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