Cilvil Diploma

Definition of Civil Drafting.

A civil drawing, or site drawing, is a type of technical drawing that shows information about grading, landscaping, or other site details.

Civil drafters prepare drawings and topographical and relief maps used in major construction or civil engineering projects, such as highways, bridges, pipelines, flood control projects, and water and sewage systems.

Architectural Drawings

An architectural drawing or architect's drawing is a technical drawing of a building (or building project) that falls within the definition of architecture. Architectural drawings are used by architects and others for a number of purposes: to develop a design idea into a coherent proposal, to communicate ideas and concepts, to convince clients of the merits of a design, to enable a building contractor to construct it, as a record of the completed work, and to make a record of a building that already exists.

Architectural drawings are drawn according to a set of conventions, which include particular views (floor plan, section etc.), sheet sizes, units of measurement and scales, annotation and cross referencing. Conventionally, drawings were made in ink on paper or a similar material, and any copies required had to be laboriously made by hand. The twentieth century saw a shift to drawing on tracing paper, so that mechanical copies could be run off efficiently.

The development of the computer had a major impact on the methods used to design and create technical drawings, making manual draughting almost obsolete, and opening up new possibilities of form using organic shapes and complex geometry. Today the vast majority of drawings are created using CAD software.

1 Size and scale

2 Standard views used in architectural drawing
- 2.1 Floor plan
- 2.2 Site plan
- 2.3 Elevation
- 2.4 Cross section
- 2.5 Isometric and axonometric projections
- 2.6 Detail drawings
3 Architectural perspective
4 Types of architectural drawing
- 4.1 Presentation drawings
- 4.2 Survey drawings
- 4.3 Record drawings
- 4.4 Working drawings
5 Drafting
- 5.1 Computer-aided design
6 Architectural reprographics

Introduction

One of the best ways to communicate one's ideas is through some form of picture or drawing. This is especially true for the engineer. The purpose of this guide is to give you the basics of engineering sketching and drawing.

We will treat "sketching" and "drawing" as one. "Sketching" generally means freehand drawing. "Drawing" usually means using drawing instruments, from compasses to computers to bring precision to the drawings.

This is just an introduction. Don't worry about understanding every detail right now - just get a general feel for the language of graphics.

We hope you like the object in Figure 1, because you'll be seeing a lot of it. Before we get started on any technical drawings, let's get a good look at this strange block from several angles.

Figure 1 - A Machined Block

Isometric Drawing

The representation of the object in figure 2 is called an isometric drawing. This is one of a family of three-dimensional views called pictorial drawings. In an isometric drawing, the object's vertical lines are drawn vertically, and the horizontal lines in the width and depth planes are shown at 30 degrees to the horizontal. When drawn under these guidelines, the lines parallel to these three axes are at their true (scale) lengths. Lines that are not parallel to these axes will not be of their true length.

Figure 2 - An Isometric Drawing

Any engineering drawing should show everything: a complete understanding of the object should be possible from the drawing. If the isometric drawing can show all details and all dimensions on one drawing, it is ideal. One can pack a great deal of information into an isometric drawing. However, if the object in figure 2 had a hole on the back side, it would not be visible using a single isometric drawing. In order to get a more complete view of the object, an orthographic projection may be used.

Orthographic or Multiview Drawing

Imagine that you have an object suspended by transparent threads inside a glass box, as in figure 3.

Figure 3 - The block suspended in a glass box

Then draw the object on each of three faces as seen from that direction. Unfold the box (figure 4) and you have the three views. We call this an "orthographic" or "multiview" drawing.

Figure 4 - The creation of an orthographic multiview drawing

Figure 5 shows how the three views appear on a piece of paper after unfolding the box.

Figure 5 - A multiview drawing and its explanation

Which views should one choose for a multiview drawing? The views that reveal every detail about the object. Three views are not always necessary; we need only as many views as are required to describe the object fully. For example, some objects need only two views, while others need four. The circular object in figure 6 requires only two views.

Figure 6 - An object needing only two orthogonal views

Dimensioning

Figure 7 - An isometric view with dimensions

We have "dimensioned" the object in the isometric drawing in figure 7. As a general guideline to dimensioning, try to think that you would make an object and dimension it in the most useful way. Put in exactly as many dimensions as are necessary for the craftsperson to make it -no more, no less. Do not put in redundant dimensions. Not only will these clutter the drawing, but if "tolerances" or accuracy levels have been included, the redundant dimensions often lead to conflicts when the tolerance allowances can be added in different ways.

Repeatedly measuring from one point to another will lead to inaccuracies. It is often better to measure from one end to various points. This gives the dimensions a reference standard. It is helpful to choose the placement of the dimension in the order in which a machinist would create the part. This convention may take some experience.

Sectioning

There are many times when the interior details of an object cannot be seen from the outside (figure 8).

Figure 8 - An isometric drawing that does not show all details

We can get around this by pretending to cut the object on a plane and showing the "sectional view". The sectional view is applicable to objects like engine blocks, where the interior details are intricate and would be very difficult to understand through the use of "hidden" lines (hidden lines are, by convention, dotted) on an orthographic or isometric drawing.

Imagine slicing the object in the middle (figure 9):

Figure 9 - "Sectioning" an object

Figure 10 - Sectioning the object in figure 8

Take away the front half (figure 10) and what you have is a full section view (figure 11).

Figure 11 - Sectioned isometric and orthogonal views

The cross-section looks like figure 11 when it is viewed from straight ahead.

Drawing Tools

To prepare a drawing, one can use manual drafting instruments (figure 12) or computer-aided drafting or design, or CAD. The basic drawing standards and conventions are the same regardless of what design tool you use to make the drawings. In learning drafting, we will approach it from the perspective of manual drafting. If the drawing is made without either instruments or CAD, it is called a freehand sketch.

Figure 12 - Drawing Tools

"Assembly" Drawings

An isometric view of an "assembled" pillow-block bearing system is shown in figure 13. It corresponds closely to what you actually see when viewing the object from a particular angle. We cannot tell what the inside of the part looks like from this view.

We can also show isometric views of the pillow-block being taken apart or "disassembled" (figure 14). This allows you to see the inner components of the bearing system. Isometric drawings can show overall arrangement clearly, but not the details and the dimensions.

Figure 13 - Pillow-block (Freehand sketch)

Figure 14 - Disassembled Pillow-block

Cross-Sectional Views

A cross-sectional view portrays a cut-away portion of the object and is another way to show hidden components in a device.

Imagine a plane that cuts vertically through the center of the pillow block as shown in figure 15. Then imagine removing the material from the front of this plane, as shown in figure 16.

Figure 15 - Pillow Block	Figure 16 - Pillow Block

This is how the remaining rear section would look. Diagonal lines (cross-hatches) show regions where materials have been cut by the cutting plane.

Figure 17 - Section "A-A"

This cross-sectional view (section A-A, figure 17), one that is orthogonal to the viewing direction, shows the relationships of lengths and diameters better. These drawings are easier to make than isometric drawings. Seasoned engineers can interpret orthogonal drawings without needing an isometric drawing, but this takes a bit of practice.

The top "outside" view of the bearing is shown in figure 18. It is an orthogonal (perpendicular) projection. Notice the direction of the arrows for the "A-A" cutting plane.

Figure 18 - The top "outside" view of the bearing

Half-Sections

A half-section is a view of an object showing one-half of the view in section, as in figure 19 and 20.

Figure 19 - Full and sectioned isometric views

Figure 20 - Front view and half section

The diagonal lines on the section drawing are used to indicate the area that has been theoretically cut. These lines are called section lining or cross-hatching. The lines are thin and are usually drawn at a 45-degree angle to the major outline of the object. The spacing between lines should be uniform.

A second, rarer, use of cross-hatching is to indicate the material of the object. One form of cross-hatching may be used for cast iron, another for bronze, and so forth. More usually, the type of material is indicated elsewhere on the drawing, making the use of different types of cross-hatching unnecessary.

Figure 21 - Half section without hidden lines

Usually hidden (dotted) lines are not used on the cross-section unless they are needed for dimensioning purposes. Also, some hidden lines on the non-sectioned part of the drawings are not needed (figure 12) since they become redundant information and may clutter the drawing.

Sectioning Objects with Holes, Ribs, Etc.

The cross-section on the right of figure 22 is technically correct. However, the convention in a drawing is to show the view on the left as the preferred method for sectioning this type of object.

Figure 22 - Cross section

Dimensioning

The purpose of dimensioning is to provide a clear and complete description of an object. A complete set of dimensions will permit only one interpretation needed to construct the part. Dimensioning should follow these guidelines.

Accuracy: correct values must be given.
Clearness: dimensions must be placed in appropriate positions.
Completeness: nothing must be left out, and nothing duplicated.
Readability: the appropriate line quality must be used for legibility.

The Basics: Definitions and Dimensions

The dimension line is a thin line, broken in the middle to allow the placement of the dimension value, with arrowheads at each end (figure 23).

Figure 23 - Dimensioned Drawing

An arrowhead is approximately 3 mm long and 1 mm wide. That is, the length is roughly three times the width. An extension line extends a line on the object to the dimension line. The first dimension line should be approximately 12 mm (0.6 in) from the object. Extension lines begin 1.5 mm from the object and extend 3 mm from the last dimension line.

A leader is a thin line used to connect a dimension with a particular area (figure 24).

Figure 24 - Example drawing with a leader

A leader may also be used to indicate a note or comment about a specific area. When there is limited space, a heavy black dot may be substituted for the arrows, as in figure 23. Also in this drawing, two holes are identical, allowing the "2x" notation to be used and the dimension to point to only one of the circles.

Where To Put Dimensions

The dimensions should be placed on the face that describes the feature most clearly. Examples of appropriate and inappropriate placing of dimensions are shown in figure 25.

Figure 25 - Example of appropriate and inappropriate dimensioning

In order to get the feel of what dimensioning is all about, we can start with a simple rectangular block. With this simple object, only three dimensions are needed to describe it completely (figure 26). There is little choice on where to put its dimensions.

Figure 26 - Simple Object

We have to make some choices when we dimension a block with a notch or cutout (figure 27). It is usually best to dimension from a common line or surface. This can be called the datum line of surface. This eliminates the addition of measurement or machining inaccuracies that would come from "chain" or "series" dimensioning. Notice how the dimensions originate on the datum surfaces. We chose one datum surface in figure 27, and another in figure 28. As long as we are consistent, it makes no difference. (We are just showing the top view).

Figure 27 - Surface datum example

Figure 28 - Surface datum example

In figure 29 we have shown a hole that we have chosen to dimension on the left side of the object. The Ø stands for "diameter".

Figure 29 - Exampled of a dimensioned hole

When the left side of the block is "radiuses" as in figure 30, we break our rule that we should not duplicate dimensions. The total length is known because the radius of the curve on the left side is given. Then, for clarity, we add the overall length of 60 and we note that it is a reference (REF) dimension. This means that it is not really required.

Figure 30 - Example of a directly dimensioned hole

Somewhere on the paper, usually the bottom, there should be placed information on what measuring system is being used (e.g. inches and millimeters) and also the scale of the drawing.

Figure 31 - Example of a directly dimensioned hole

This drawing is symmetric about the horizontal centerline. Centerlines (chain-dotted) are used for symmetric objects, and also for the center of circles and holes. We can dimension directly to the centerline, as in figure 31. In some cases this method can be clearer than just dimensioning between surfaces.

Orthographic Projection is a way of drawing an 3D object from different directions. Usually a front, side and plan view are drawn so that a person looking at the drawing can see all the important sides. Orthographic drawings are useful especially when a design has been developed to a stage whereby it is almost ready to manufacture. IMPORTANT: There are two ways of drawing in orthographic - First Angle and Third Angle. They differ only in the position of the plan, front and side views. Below is an example of First Angle projection.

Opposite is a simple L-shape, drawn in three dimensions. The front, side and plan views have drawn around the 3D shape. However this is not the correct way of drawing them as they are not in the right positions.



The correct method of presenting the three views, in first angle orthographic projection is shown below. The drawing is composed of a front, side and plan view of the L-shaped object. The first drawing is the front view (drawn looking straight at the front of the L-shape), the second is a drawing of the L-shape seen from the side (known as side view) and last of all a drawing from above known as a plan view. The red lines are faint guidelines and they are drawn to help keep each view in line, level and the same size. Please Note! This is an example of first angle orthographic projection (as used mainly in Europe). There is another type called third angle which is used by countries such as the USA. The front, side and plan views are in different positions



THE SIDE VIEW
		Imagine standing directly at the side of the L shape.
THE FRONT VIEW
		Now imagine standing directly in front of the L-shape, the drawing opposite shows exactly what you would see.

THE PLAN VIEW

		The plan view is a view seen directly from above. Some people call this a birds eye view.




Draw an orthographic projection of a H-shape. Clearly show the front, side and plan views and use guidelines to keep them level.

Carefully study the symbols shown below. Normally when drawing in first or third angle projection a symbol is drawn underneath which clearly shows which angle of projection has been used.

PDF FILE - CLICK HERE FOR PRINTABLE VERSION OF EXERCISE BELOW



Another example of first angle orthographic projection is shown below. Follow the blue, red and green guidelines as the front, side and plan view are constructed.


The final arrangement of the views are shown in the drawing below. Notice how the symbol for first angle orthographic projection has been added and the paper has a title block and borderline.

Section

The act of cutting, or separation by cutting; as, the section of bodies.

A part separated from something; a division; a portion; a slice.

A distinct part or portion of a book or writing; a subdivision of a chapter; the division of a law or other writing; a paragraph; an article; hence, the character /, often used to denote such a division.

A distinct part of a country or people, community, class, or the like; a part of a territory separated by geographical lines, or of a people considered as distinct.

One of the portions, of one square mile each, into which the public lands of the United States are divided; one thirty-sixth part of a township. These sections are subdivided into quarter sections for sale under the homestead and preemption laws.

The figure made up of all the points common to a superficies and a solid which meet, or to two superficies which meet, or to two lines which meet. In the first case the section is a superficies, in the second a line, and in the third a point.

A division of a genus; a group of species separated by some distinction from others of the same genus; -- often indicated by the sign /.

A part of a musical period, composed of one or more phrases. See Phrase.

The description or representation of anything as it would appear if cut through by any intersecting plane; depiction of what is beyond a plane passing through, or supposed to pass through, an object, as a building, a machine, a succession of strata; profile.

Lettering

Uniformity is one of the main requirements for good lettering.
Never mix upper and lower case letters
Background areas between letters should appear as equal.
Space between words should be equal.
Use these block style capital letters on your drawings.

Vertical Capital letters

Study the chart to see how the shape of each letter is made.

The Title Block: shows all the necessary information not shown on the drawing itself. This shows drafter's name, date, name of the drawing, the scale it was drawn in and the dimensions.
JOHNNY TRUESTORY

1/31/11

TABLE DRAWING

1:5 SCALE

DIMENSIONS IN MM
Draw the title block in an open area in the upper right portion of the drawing.
Use the block lettering style to letter the drawing.

Dimensioning

A drawing must be complete so that the object represented in it can be made exactly as intended.
Drawing must tell two complete stories.
One method = Views
Another way to tell the story is through the dimensions.
Whether the views are drawn to full size or to scale, the dimensions must be the actual dimensions of the completed object.
Correct dimensions are absolutely necessary. Wrong dimensions may not be discovered until we are deep into the manufacturing process and by then we have made 11,546 widgets.
Such a mistake could cost the drafter her/his job!

Dimensioning standards = types of lines, spacing dimensions, correct arrowheads, dimension figures, etc.
4 types of lines used in dimensioning: extension line, dimension line, center line and leader.
Extension line: extends a line from the object. Leave a gap of about 1/16" next to the object. Continues about 1/8" beyond the outermost arrowhead. Never leave a gap where an extension line crosses any other line.
Dimension line: Has an arrowhead at each end indicating the length of the dimension. A gap is left in the middle of the dimension line for the dimension figure.
Don't crowd the drawing with dimension lines. Keep enough space between the lines and the drawing.
Space dimension lines consistently throughout the drawing.
Center lines: used to indicate axes of symmetry. Used in place of extension lines for locating holes and other features. Make center lines end about 1/4" outside the hole or feature, unless it is needs to extend to assist in creating another dimension.
Leader lines: leads from a note or dimension and ends with an arrowhead touching the part to which attention is directed. Always inclined lines, never vertical or horizontal. Usually drawn at 30°, 45° or 60°.
A short horizontal should should extend from the leader line. Lettering extends from the middle of the shoulder line.

Arrowheads:Drawn with two sharp strokes toward or away from the point. Should be about 1/8" long. Fill in the arrowhead. Avoid sloppy, careless arrowheads.

Standard height for whole numbers is 1/8" and the standard height for fractions is 1/4".
Never letter a dimension figure over any line of the drawing.
Dimensioning angles: angles are drawn with triangles. When degrees for the angles are given, the circular dimension lines are drawn with the compass center at the vertex of the angle. Dimensions are lettered horizontally.

Dimensioning Arcs: Arcs are dimensioned in the views in which their true shapes appear by giving the radius of the arc. Print the letter R, for radius, before the actual dimension.
If the space is too crowded, move the dimension figure outside the arc.

Dimensioning Fillets and rounds: Not necessary to give the dimensions of every fillet and round, but only a few typical radii of these.
Placement of dimensions: smallest dimensions should be placed nearest the object;then line up the rest of the dimensions moving outward, smallest to largest.
Overall dimensions are always farthest from the view.
Avoid placing dimensions where dimension lines cross extension lines.
Never place a dimension touching a line of the drawing or join it end to end with a line of the drawing.
Avoid placing dimensions on a view. Sometimes this is too difficult to solve, not enough room.
Avoid placing dimension so that extension lines cross lines of the drawing .
Extension lines may cross each other freely.
Extension lines should never be shortened.
Often, extension lines must cross the lines of the drawing.

Steps in applying dimensions

Draw extension lines dark and sharp. Extend the center lines of the holes in the same manner as the extension lines.
Use the scale to space the dimensions at least 3/8" from the object and 1/4" apart.
Draw the dimension lines dark and sharp, leaving gaps for the dimensions.
Draw all arrowheads about 1/8" long and very narrow.
Add all dimension figures and lettering.

Pictorial Drawings

Pictorial drawings provide a 3D image to help understand a drawing
The most common pictorial drawing is the Isometric drawing. The isometric view provides a likeness of the 3D object and should be drawn to provide as much detail as possible. The lengths of lines are generally the true length of the object. (Sometimes the view may be scaled)
Perspective drawings provide the most accurate view of an object but the measurements are not true lengths.
Axonometric (planometric) views are often used on house plans to show room interiors.
Check information on How to complete Isometric drawings
Below is an example of the use of a axonometric/planometric projection