Drawing an arc is easy using AutoCAD and there are many uses of this entity like for example drawing complex shaped objects etc. etc. But first let me introduce to you what an an ARC is. Basically it is part or portion of a circle that is why the correct way of measuring an ARC is by it’s radius. Look at the drawing below (Fig 1). You can see that an arc is a portion of a circle and the center of the circle as a reference point to measure the radius, included angle and chord. The length of an ARC is determined by the measurement of the included angle between the radius and chord from the arc’s endpoints.

Fig.1

So how to draw an ARC using AutoCAD? There are many options of drawing an ARC in AutoCAD but in the real world drafting you usually use 2 or 3 of them telling from my experience. But I’m not sure in other discipline of AutoCAD users. My drafting job is usually mechanical just for the info. In version 200, there are 11 ways to draw an Arc namely:

• 3 points
• Start, Center, End
• Start, Center, Angle
• Start, Center, Length
• Start, End, Angle
• Start, End, Direction
• Start, End, Radius
• Center Start, End
• Center Start, Angle
• Center Start, Length
• Continue

The 3 Point ARC

To draw a 3 point arc, you just need to select in the menu Draw>Arc>3 Points then pick a point on your screen for the first point of your arc (See Fig. 2 - The little circle on the arc is just an illustration to see which point are the 3 points in the ARC. You will not see it while making the drawing. ). Then the command prompt will say: Specify second point of arc or [CEnter/ENd]: which means you have to pick a second point to draw the ARC. After picking a point on the screen, the command prompt will tell you again to: specify end point of arc: obviously, AutoCAD is asking you to pick the third point of the arc. After clicking then you have drawn your first ARC ( Hurray!)

Fig. 2

Start, Center, End

Again go back to the menu and choose Draw>Arc>Start, Center, End. This time the method is different from 3 points because you need to specify a radius of the arc then afterwards the arc will depend on how you want to make your arc on the last command. So to start making the ARC and after you selected the menu I mentioned above, pick a point on the screen by clicking your mouse. Then AutoCAD will prompt: Specify second point of arc or [CEnter/ENd]: _c Specify center point of arc: (See Fig. 3). The second point is actually the radius of the arc and you can specify a dimension. But this is optional in this tutorial and you can pick the second point on any part of the black screen. If you want to draw ab object with the exact dimension, then you can specify a radius. After picking the second point, you will notice that you can drag the arc by making a circular movement. Then AutoCAD will prompt again: Specify end point of arc or [Angle/chord Length]: then it’s up to you where to pick the point or how long you want your arc to be.

Fig. 3

Start, Center, Angle

This is similar to the previous method Start, Center, End but this time you have to specify the included angle. I assume you already know the measurement of angles from zero degrees to 360 degrees. Again go back to the menu and choose Draw>Arc>Start, Center, Angle. Then pick your first point on the screen then AutoCAD will prompt again: Specify second point of arc or [CEnter/ENd]: _c Specify center point of arc: Then after picking your second point AutoCAD will prompt again: Specify end point of arc or [Angle/chord Length]: _a Specify included angle: Which means you have to specify your desired angle to make the arc (See Fig.1 for reference). You can type the angle you desire in the command prompt, let say 90, which means 90 degrees then press enter.

You can also draw it with out typing the degrees by just dragging the cursor but it seem not very useful so I’ll just omit it. But just for additional knowledge, maybe I’ll discuss it further. Notice when drag your cursor up and down or left to right, the ARC elongates and shrink? it only follows the cursors when you rotate it counter clock wise. Zero degrees starts from the right quadrant and when you rotate your cursor counter clockwise it begins to give the arc the degrees measurement (See Fig. 4).

Fig. 4

Start, Center, Length

Again this is very similar with the past two method of drawing an ARC which started from a point, then goes to the center( for the radius length). But this time it won’t ask for the included angle. It will ask for the chord length.

Again go back to the menu and choose Draw>Arc>Start, Center, Length. Then pick your first point on the screen then AutoCAD will prompt again: Specify second point of arc or [CEnter/ENd]: _c Specify center point of arc: Then after picking your second point AutoCAD will prompt again: Specify end point of arc or [Angle/chord Length]: _l Specify chord length: Which is asking you to specify the length of the chord to create the arc (See Fig. 5). You can drag your cursor and click any point in the screen. The white line you see that stretches and stick with the cursor on one end and to the first point you pick on the other end represent the length of the chord.

Fig. 5

So this is the end of part 1. Ill discuss part 2 on my next post. If there is something you want to know about AutoCAD, please make a comment so I can create a tutorial about it.