AutoCAD Modify Tools
While working with AutoCAD, you'll quickly run into situations that requere you to use modify tools. As the name sugestes, modify tools are used to modify existing lines and objects.
AutoCAD has a whole range of modify tools; this chapter will explain the most commonly used.
Create a duplicate object parallel with the original object. If this object is a Polyline or a Circle, the duplicate shape will be transformed inwards or outwards. This option can be useful to make closed steel profiles.
To offset: First select the offset distance; [enter]; select the original object; specify on which side you want to offset.
With the trim option objects can be shortened or lengthened with the edges of other objects. Objects can exactly be fitted between these objects.
To trim an object: Type tr in the command line; optionally select the line(s) you want to trim (otherwise all objects are used, which is fine in most cases); [enter]; select the objects to trim.
To trim multiple objects at once you can drag a selection window.
With the extend option you can shorten or lengthen objects to meet the edges of other objects. For example a line can be exactly fitted between objects. Extending a object works in the same way as trimming.
To extend: Click the Extend command; optionally select the object you want to extend to; select the line(s) you want to extend.
Moves one or more objects:
Select the objects and specify the base point.
The base point is essentially the point where you 'grab' the objects. So if you input coordinates, the base point is the point where the coordinates relate to.
Moving an object can either be done with the aid of object snap, or by using relative coordinates.
You can rotate objects with an absolute or relative angle. When using an absolute angle: Specify the base point and then specify the rotation angle.
Copy's one or more objects.
Select objects, press copy and specify a base point (in a similar fasion as with the move tool)
Now you can position the object in the same way as you would with a starting point of a line.
Create copies of objects in a rectangular or polar pattern. This is especially useful when you need to duplicate several objects at the same distance from each other (columns in a parking garage for instance).
After clicking on the array button the following screen will appear:
In this screen we need to input the number of Rows (horizontal direction) and Columns (vertical direction) and their respective offset.
We're going to create a grid of I-beams, lets first input the number of rows and columns (in this case 3 and 4). Now input the row and column offset: 30 units to the right and 20 units upward.
AutoCAD automatically shows a preview of the array operation in the white square, try experimenting with different values (for instance a negative value instead of a positive one) to see what happens.
When you're satisfied with the settings, select the object to use in the row operation, by first clicking on the 'Select Objects' button and then on the objects themselves.
Finish the selection by pressing [space] or [enter]
When the array window reappears, select either Preview or OK to execute the array command.
In the same manner it's possible to create a polar array:
The polar array rotates around the center point which you can select by clicking on the center point button in the array window.
Create a mirror image of a object. It is useful for creating symmetrical objects because you can quickly draw half the object and then mirror it instead of drawing the entire object.
You flip the object about an axis called a mirror line to create a mirror image. First select the object. To specify the temporary mirror line, you enter two points. You can choose whether to delete [y] or retain the original [n] object.
To scale an object you can specify a base point and a length, which will give a scale factor. A scale factor greater than 1 enlarges the object. It is also possible to scale an object using a reference object. This method scales the object equally in all directions.
Scaling using a scale factor: Select the object; type sc in the command line; scale factor; [enter]
Scaling using a reference: Select the object; type sc in the command line; specify base point; choose r to use reference; specify the reference length of the original object; specify the new length of the original object.
You can use the fillet tool to connect two objects with an arc with a specified radius. The inside corner is called a fillet and an outside corner is called a round.
To fillet: type f in the command line; type R for the radius (optional); specify the radius; [enter]; select the first line; select the second line.
Chamfer is almost identical, but it will will make a straight line instead of an arc.
You can use the join option to combine similar objects into one single object. It is also possible to create complete circles from arcs.
The object you want to join is called the source object. And the objects you want to join have to be located in the same plane.
To join: Type j in the command line; select the source object; select the lines to join to the source object.
If you use AutoCAD 2009 or older, you can only join lines when the endpoints of the lines are on one point.
Polylines, hatches or blockes can be converted into individual elements with the explode option.
If you explode a polyline every segment will become a separate line.
To Explode a block: First select the block; type ex; [enter].