Computer Studies
 Knot Making

Modify Commands - Part 3


Command: lengthen or len

With this command you can lengthen or shorten a variety of objects including lines, polylines and arcs.

Command: len
Select an object or [DElta/Percent/Total/DYnamic]: select object
Current length: 800.0000, included angle: 79
Select an object or [DElta/Percent/Total/DYnamic]: …..

When the lengthen command is invoked, you are prompted to select an object. In the command line example presented, the object selected was an arc of length 800 and included angle 79. AutoCAD returns those values to inform the user of the current properties of the object being lengthened. If a line was selected instead, only the length of the line would be returned to the user. You can select more objects and ACAD will inform you of their current length and angle.

When you are ready to lengthen objects, you have four options to choose from; delta, percent, total and dynamic. Delta

With the delta option you specify the amount the object will be increased or decreased by. The prompt sequence to lengthen an object by 100 units is:

Select an object or [DElta/Percent/Total/DYnamic]: de
Enter delta length or [Angle] <0.0000>: 100
Select an object to change or [Undo]: press enter

With this option, to shorten an object a negative number is specified and the object’s length will be decreased by that amount.


With the percent option, you specify the percentage change in the object’s length. The prompt sequence to lengthen an object by 50% of its size is:

Select an object or [DElta/Percent/Total/DYnamic]: p
Enter percentage length <100.0000>: 150
Select an object to change or [Undo]: press enter

Obviously enough, a number smaller than 100 will shorten the object.


With the total option you specify the desired total length of the object irrelevant of its current length. The command prompt sequence to lengthen/shorten an object to 400 units is:

Select an object or [DElta/Percent/Total/DYnamic]: t
Specify total length or [Angle] <1.0000)>: 400
Select an object to change or [Undo]: press enter


With the dynamic option, you choose one endpoint of the object and dynamically drag it to change its position.

Select an object or [DElta/Percent/Total/DYnamic]: dy
Select an object to change or [Undo]: select object from endpoint to be changed
Specify new end point: drag endpoint to new position and click


Command: array or ar

Some times you need to copy an object for a number of times and it is time consuming to do by the copy command. The array command allows you to create an array of the same object. There are two types of array you can create; a rectangular array and a polar array. With the rectangular array, you will create multiple items of the object that will be placed in a rectangular fashion, and with the polar array, the objects will be placed around a circle or arc.

When you invoke the array command you will be presented with the ‘Array’ dialogue box. At the top of the dialogue box are two mutually exclusive radio buttons ‘Rectangular Array’ and ‘Polar Array’. Select which kind of array you wish to create. Next to the radio buttons is another button ‘Select objects’, and just underneath it the number of objects that are selected. Click this button and select the objects you wish to apply the command to.

For the rectangular array, you need to specify the amount of rows and columns you want in the array. The default is 4X4 which will thus create 16 copies of the selected object. Modify those as necessary. The row and column offset are the distances from the center point of one object to the center point of the next. Notice this is not the distance by which objects are separated. Next to the row offset and column offset text boxes are three buttons. The first larger button allows you to dynamically specify a rectangle, the corners of which will be equal to the offsets. The other smaller buttons allow you to select distances dynamically that will specify the row offset and column offset separately. The angle of the array is the angle at which the rows are drawn from the horizontal.

With the polar array you have to specify a center point around which the items will be rotated. Enter the coordinates in the text boxes, or click the button next to them to select the center point dynamically. There are three methods to specify a polar array;

Total number of items and Angle to fill (default option)
Total number of items and Angle between items
Angle to fill and Angle between items

Choose your preferred one from the drop down list, and fill in the rest of the variables which are quite self explanatory. Do not miss out the ‘Rotate items as copied’ check box at the bottom. If this is selected it means that the object will be rotated around the center of the array. For instance, if you are drawing chairs around a table then you would probably want to select this option.

When you are done with all the variables, you can either select ‘ok’ to apply the array right away, or you can select ‘preview’. Selecting preview rather than ok allows you to view the array before applying it in order to be able to make any changes just in case you have input some incorrect dimension. While in preview mode, press ‘esc’ to return to the ‘Array’ dialogue box or press ‘enter’ to accept the current array.


Command: mirror or mi

The mirror command is used to create a copy of an object that is mirrored about a line called the mirror line. The mirror line is like the line of symmetry. When you invoke this command, you will be prompted to select the objects to be mirrored and then to specify the mirror line (line of symmetry) by indicating two points that lie on this line:

Command: mi
Select objects: select objects
Select objects: press enter to indicate all objects have been selected
Specify first point of mirror line: specify first point
Specify second point of mirror line: specify second point
Erase source objects? [Yes/No] : press enter

At the end of the command prompt you are also asked if you wish to erase the source object. The default is ‘no’ and if you just press enter, the source object will not be erased. To erase it and keep the new mirrored copy only, type ‘y’ and press enter.

Note: If you mirror text, AutoCAD will create a copy of the text at the mirrored location as with all other objects, but the text will not be mirrored so as to still read correctly. If you wish to mirror text just the same, you have to set the system variable ‘mirrtext’ to ‘1’ before invoking the mirror command. You can reset mirrtext to the default value ‘0’ at any time. The command prompt sequence is presented below:

Command: mirrtext
Enter new value for MIRRTEXT <0>: 1


Command: break or br

There are two slight variations of this command; the ‘break’ command and the ‘break at point’ command.

The ‘break’ command

This is used to break a single object into two by selecting two points on the object. The space in between these two points is erased leaving you with two separate objects on each end. The command prompt sequence is as follows:

Command: br
BREAK Select object: select object at first break point
Specify second break point or [First point]: specify second break point

If you have selected the object from a point other than a break point, you are still given the option to specify the first point by typing ‘f’ rather than specifying the second point. This will allow you to specify both break points again.

The ‘break at point’ command

This command is used to break a single object into two at one break point, thus leaving no space in between. Strictly this may be considered either a variation or a different command; in the modify toolbar/panel there is a different button for this command, but the command is still break or br. The prompt sequence is in fact almost the same as the previous one:

Command: br
BREAK Select object: select object at break point
Specify second break point or [First point]: @

Notice the ‘@’ entered rather than a point being specified. This means the object is broken at the first point only.

Measure and Divide

Command for Measure: measure or me
Command for Divide: divide or div

Measure and divide are two very similar operations. They both split an object into a number of parts without breaking it. Thus you are still left with one object, but after the command you will have points indicating where the object is split at.

With the measure command, you determine the distance between one point and the next and AutoCAD will mark these points on the object. With the divide command you determine the number of parts you want the object divided into and again AutoCAD will mark the points:

Command: me
Select object to measure: select object
Specify length of segment or [Block]: 100

Command: div
Select object to divide: select object
Enter the number of segments or [Block]: 10

If nothing seems to happen, you probably have the pdmode system variable set to ‘0’. This system variable, as you may remember from previous tutorials is used to set the way points are displayed. Set it to a value of ‘3’ to make the points visible.


Command: explode or x

Do not use this command! It will blow off your pc… ok all it does is break compound objects apart. You may have a rectangle or polyline for example, and you wish to edit its various components separately. Command prompt sequence is very simple, but here it is anyway just for the record:

Command: x
Select objects: select object/s
Select objects: press enter

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