Tips from CADD Primer:
Erasing Drawing Objects:
CADD provides a fast, accurate and convenient means of erasing drawings. Once you have entered the erase command, you are in the erase mode; any objects you select now will be instantly erased. You can use any method described above to select the objects.
The erase function is very powerful; it must be used with great caution. It can erase large amounts of information within seconds. If you make a mistake while erasing, be sure to take quick action. You can use the undo feature of CADD to disregard the effect of the last command.
Moving Drawing Objects:
CADD allows you to move drawing objects within a drawing in a convenient manner. Unlike on a drawing board, you don't need to first erase and then redraw in a new place. You can simply rearrange the existing drawing objects, as you like. This is a very useful tool for analyzing design alternatives and making quick adjustments to drawings.
To move the objects, you need to enter the move function and select the objects to be moved. Enter a base point and a relocation point (destination point) and the selected objects are moved. The base point acts as an anchor for the selected objects and relocation point determines the new location of the selected objects. The objects are moved relative to the base point and the relocation point. Let’s say you indicate the relocation point 4’-0” to the right of the base point. All the selected objects will be moved 4’-0” to the right.
Fig. 5.2: Moving objects using the move function.
Copying Drawing Objects:
CADD allows you to make quick and easy copies of existing drawing objects. You can copy individual drawing objects or the entire drawing all at once. You can even make multiple copies of drawing objects within seconds.
Using the copy function is quite similar to the way the move function is used. First, you need to select objects using any of the methods described earlier. Then you need to indicate a base point and a relocation (or destination) point. The copied objects are placed according to the relocation point.
Making Multiple Copies in a Rectangular Form
There are separate functions available in CADD that allow you to make multiple copies in a linear or rectangular form (commonly known as a rectangular array). You can make hundreds of copies within seconds. You don't need to enter a base point and a destination point. You just need to select the objects, specify how many rows and columns you need and the distance between them.
Fig. 5.3 illustrates how you can make multiple copies of a chamfered shape diagram. To make five copies of the original shape as shown in Diagram A, you need to specify that the copies be made in two rows and three columns. Enter the distance between the rows as 3/4” and the distance between the columns as 1”. Similarly, you can make 44 copies of the original by specifying 5 rows and 9 columns as shown in Diagram B.
Making Copies in a Circular Form
CADD allows you to make multiple copies of selected objects in a circular form (commonly known as a polar array). You need to enter the center point of array, number of copies required and the rotation angle. The center point of the array is a point around which the copies are arranged. The rotation angle determines the extent of the rotation, and the number of copies you specify are equally spaced between the rotation angle.
Fig. 5.4 illustrates how you can make multiple copies of a chair around a table. Diagram A shows the original. In Diagram B, seven copies of the chair are made to fit around half the table (rotation angle 180). In Diagram C, the same number of chairs fit around three-quarters of the table (rotation angle 270) and in Diagram D, they fit around the complete table (rotation angle 360).
Changing Drawing Appearance:
CADD allows you to change the appearance of drawing objects in a number of ways. You can change the line type, color, size and style of all the drawing objects. Using the editing functions of CADD, you can change almost every factor that defines a drawing object.
When you enter a command to change the drawing appearance, you are prompted to select the objects you want to change. You can select the objects using any of the methods discussed earlier. After the selection is made, you can specify what you want to change, and the selected objects are changed accordingly.
The edit functions allow you to do the following:
• Change line type, color and layer of drawing objects.
• Change the radius value of arcs and circles.
• Change major-axis, minor-axis and rotation angle of the ellipses.
• Change the thickness and flow of splines.
• Change the height, width, spacing, inclination, fonts and justification of text.
• Change the size, style, units, and accuracy of dimensions.
• Change the size and style of symbols, arrows, borders, and patterns.
Using Edit Functions as a Drawing-Aid Tool
The edit functions enable you to manipulate diagrams and make quick corrections in the following manners:
• Cutting drawing objects along an edge
• Drawing parallel lines and arcs
• Extending drawing objects to an edge
• Dividing an object into equal parts
• Making sharp and rounded corners
• Making chamfered corners
• Stretching a diagram
• Enlarging or reducing a diagram
• Rotating a diagram
• Mirroring a diagram
Cutting Drawing Objects Along an Edge:
CADD allows you to erase drawing objects along a selected edge (this technique is often called trimming). When you use this function, you are prompted to select the drawing object that is to be used as the cutting edge and then select the objects that are to be erased along that edge.
Fig. 5.5 illustrates how you can erase lines along the edge of an arc. The diagram to the left (original) shows the lines crossing the arc. The second diagram shows that the arc is selected as the cutting edge. In the next diagram, the lines falling outside the arc are selected as the lines to be trimmed. The fourth diagram shows the result of trimming the lines along the arc.
Fig. 5.5: Trimming lines along an arc.
Drawing Parallel Lines and Arcs:
CADD allows you to draw parallel lines, arcs or splines using previously drawn objects as a reference. This technique is often called offsetting. To draw an offset parallel line, you need to select the drawing object to be used as a reference and then specify the distance and direction of the offset. A parallel drawing object is drawn at the specified distance.
Fig. 5.6 shows how you can draw multiple lines, arcs and splines using a single object as a reference. The dark lines shown in the diagram represent the original drawing objects. The rest of the drawing objects are drawn as an offset of the original. When the first offset is drawn, it can be used as a reference to draw the next parallel drawing object.
Note: When drawing an offset to the inside of an arc, you cannot enter a greater value for the offset than the radius of the selected arc. Such an arc is not possible to draw and the computer displays an error message.
Extending Drawing Objects to an Edge:
CADD allows you to extend lines to a selected drawing object. Often you need to extend lines to construct a drawing and to fix any graphical errors. To extend lines, you need to select an edge to which the lines should extend and then select the lines to be extended. Fig. 5.7 shows how you can extend a number of lines to an edge formed by a line and arcs.
Dividing an Object into Equal Parts:
CADD allows you to place dividing marks on a drawing object such as a line, arc, ellipse or spline. To use this command, you need to select an object and specify how many divisions are required. This function places markers at equal distances on the drawing object.
Fig. 5.8 shows how you can divide an arc, an ellipse, a line and a spline into equal parts. It takes only seconds to place the dividing markers and you don’t need to do any calculations. The divisions are accurate to the last fraction and the results can be used for any calculation.
Note: The markers drawn are only for reference, they do not break the drawing object. You can erase the markers when you are finished using them.
Making Chamfered Corners:
CADD allows you to make a chamfered corner between two lines. It works quite like the fillet command. When you enter the chamfer command, you are prompted to select the lines that are to be chamfered and enter a chamfer distance. The chamfer distance determines the size of the chamfer. Fig. 5.9 shows how you can make a chamfered corner between two lines that are set apart.
Making Sharp and Rounded Corners:
CADD allows you to make fine corners of any two lines or arcs. This technique, often called filleting, is the quickest way to join the missing corners of lines and arcs. With this function active, to make a corner all you need to do is select the lines or arcs that have missing corners. CADD automatically extends or shortens the selected objects to form a corner. You can also specify whether you want a sharp corner or a rounded corner.
Fig. 5.10 shows how you can join the missing corners of lines and arcs. Diagram A shows how to make a sharp corner of two lines that are set apart. Diagram B shows how to make rounded corners between lines and arcs. When making a rounded corner you can specify the radius of the arc that is to be used to create the fillet.
CADD allows you to quickly change the size of diagrams by stretching lines, arcs, splines, etc. This function is very helpful to make quick alterations to drawings. To use the stretch function, you need to select the drawing objects to be stretched and specify the distance and direction of stretching.
Fig. 5.11 shows how you can stretch a rectangular-shaped diagram to make it longer. The objects to be stretched are selected by enclosing them in an editing window formed by points 1 and 2. The diagram is stretched in the horizontal direction by 1”.
Note: When dimensions are stretched, the program updates the dimension values automatically. When text and symbols are stretched, their appearance remains unchanged but they are relocated. When only one end of an arc is stretched, it may deform the shape of the arc.
Enlarging or Reducing Diagrams:
CADD allows you to enlarge or reduce diagrams in a convenient manner. To enlarge or reduce diagrams, you need to select the objects and enter a scale factor. The scale factor determines by how much the diagrams are to be reduced or enlarged.
Example: To reduce a 10'x20' square to a 5'x10' square, you would need to enter a scale factor of 0.5. Similarly, to enlarge the diagram to twice its original size, you would need to enter a scale factor of 2. You can precisely reduce or enlarge the diagrams by entering an exact scale factor. Fig. 5.12 shows how you might enlarge a portion of a diagram four times to show it in more detail.
Rotating the Diagrams:
CADD allows you to rotate selected drawing objects to a specified angle. To rotate, you need to select the drawing objects, enter a reference point (or base point) and the rotation angle. The base point acts as a pivot point around which the objects are rotated. The rotation angle determines by how much the objects will be rotated and in which direction.
Fig. 5.13 illustrates the ways you can rotate a drawing 45 by indicating different base points. The diagram on the left shows how the drawing is rotated when the base point is entered in the middle of the drawing. The diagram in the middle shows the rotation when the base point is entered at a corner. The diagram on the right shows what happens when the base point is entered away from the drawing.
Mirroring the Diagrams:
CADD allows you to create mirror images of selected drawing objects. This capability is very useful when you want to draw something that is symmetrical on both sides. You need to draw only one half of the drawing; the rest of the drawing can be completed using the mirror function. To make a mirror image, you need to select the objects to be mirrored and indicate a mirror axis. The mirror axis is an imaginary line along which the diagram is mirrored. Fig. 5.14 illustrates how you can draw a complete flange drawing from only half the drawing.
Steps to Draw an Engineer’s Office:
Here is an exercise to draw a plan of a room called engineer’s office. The engineer’s office is 19 feet, 6 inches long and 13 feet, 6 inches wide. It has a chamfered corner on one side and has a door in the opposite corner. We will accurately draw this plan using drawing, editing and view-display functions.
The exercise is completed in 24 steps (Fig. 5.16 to 5.21). First, we will complete the plan of a single room (Fig. 5.16 to Fig. 5.19). We will use this plan to make a 4-unit office block as shown in Screen 24 Fig. 5.21. Later, we will describe how to use this office block to make a complete engineering complex as shown in Fig. 5.22.
The objective of this exercise is to give a general overview of working with edit functions. The illustrations show only the basic steps required to complete the drawing. The exact procedures vary from one program to another.
For illustration purpose, only the tool buttons required in the exercise are shown. Fig. 5.15 shows some of the examples.