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Sometimes when working in a drawing, you may be tempted to reach for your handheld calculator to solve a quick equation. However, in most cases the handheld calculator isn't necessary. You see AutoCAD has a builtin calculator capable of solving nearly any equation and it will do it without leaving the active command. In this lesson we're going to learn how to use AutoCAD's Command Prompt Calculator. On my screen I have a simple polygon. Let's see if we can recreate this geometry. I'll start by opening the Draw panel and I'll watch the Polygon command.
Since this is a hexagon, I will enter 6 for my number of sides and I'll press Enter. I will then click to specify the center point and since the original polygon is dimensioned to the edges, this must be a circumscribed polygon. Now what's the radius? Well, I know the diameter is 6.763. So the radius must be half of that. Since I don't know the exact radius, I'm going to type 'cal and press Enter. This brings up AutoCAD's Command Prompt Calculator where I can enter my equation.
The nicest part of this calculator is that whatever value I come up with, AutoCAD is going to apply it to the active command. I'll type 6.763/2 and I'll press Enter. As you can see, AutoCAD did the math for me and it finished the polygon. Anytime AutoCAD asks you for a number, you can type 'cal to launch the Command Prompt Calculator. Let's pan this over. In addition to doing mathematical expressions, the calculator also has some prebuilt functions.
For instance over here I have a line that's been offset. Let's say I would like to offset this green line the same distance as these original lines. I'll launch the Offset command and when AutoCAD asks for the distance I'll type 'cal. And for my expression, I'll type dee. This stands for distance between two endpoints and I'll press Enter. I will then select the endpoint of this line and the endpoint of this line. As you can see, AutoCAD calculated the distance between those points and it's applying that value to the active command.
So I can simply click my green line and then choose the side where I'd like to create my offset. We can even mix and match functions with expressions. Maybe I'd like to find the center line between these two entities. I'll press my Spacebar to relaunch Offset. For my distance I'll type 'cal and the expression will be dee/2. I will then select this endpoint and this one. AutoCAD does the calculation.
I will select this line and I'll offset it to this side. Let's pan this over and look at another expression. On my screen I have a large circle. Let's say I would like to fillet these two line segments using the same radius as this circle. I'll launch the Fillet command. I will rightclick to access the Radius option and when AutoCAD asks for a radius, I'll type 'cal. For my expression, I'll type rad and press Enter.
I will then select this circle. AutoCAD extracts the radius from that geometry and applies it to the current command. I can then select this line and this line to create my fillet. Now let's say I'd like to fillet these lines using a radius twice the size of the original circle. I'll press my Spacebar to go back into the Fillet command. I'll rightclick and select the Radius option. For my Radius I'll type 'cal. The expression will be rad*2, and I am using the Asterisk key to represent multiplication.
I will then select the circle and then I'll select my two lines. Finally let's pan this over. You can even incorporate object snaps into your expressions. As an example, let's say I wanted to create a circle at the center of this equilateral triangle. I'll launch the Circle command and when AutoCAD asks for a center point I'll type 'cal and I'll press Enter. My expression will be (end+end+end).
I'd like to take that value divided by three and I'll press Enter. I will then select this endpoint, this one and this one, and AutoCAD adds up the coordinates and divides them by 3 to find the center. The calculator is one of AutoCAD's most powerful features and in this lesson we've only scratched the surface on what this tool can do. For more information on using AutoCAD's calculator, type 'cal at the command line and at the Expression prompt press the F1 key to access contextsensitive help.
You'll be amazed that how far this tool can take you.