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AutoCAD Essentials is a multi-part series that takes a more modular approach to this massive program, used for everything from 2D and 3D CAD design, drafting, and modeling to architectural drawing and engineering projects. In this installment, author Jeff Bartels concentrates on the particulars of creating basic geometry in AutoCAD, including assigning imperial or metric units of measurement, using object snaps to control accuracy, and drawing and transforming basic lines and shapes. The last chapter in the course tests your newfound skills in a short project.
AutoCAD is used by several disciplines to create many different types of construction drawings. For this reason, AutoCAD allows us to draw using virtually any unit of measure that we like, whether it be inches, millimeters, feet, or something else entirely. In this lesson, we're going to learn how to assign a unit of measure to a drawing. As you can see, I've just launched my AutoCAD and I'm sitting in the default Drawing1 file. I'd like to start by drawing a line, so I'll move up and launch the Line command, I'll pick a point onscreen and then I will pull to the right. The angle isn't important right now. I just liked to create a line that is one unit long, so I'll type 1 and hit Enter.
When I'm finished, I'll press Escape. I will then roll my mouse wheel forward. We'll zoom in on this line a little bit. Now, my question is, What unit of measure does this line represent? Is this line one foot? Is it one mile? Could it be one millimeter? Well, this line represents whatever unit of measure I want it to represent. All I have to do is let AutoCAD know the units I'm using. To do that, I'll open the application menu, I'll come down to Drawing Utilities, and then I'll come over and select Units. This brings up the Drawing Units dialog box, and I can see right here the default unit of measure that's assigned to this file.
So technically, this line represents one inch. If I open the menu, you can see that there are several other choices. The more popular ones are up towards the top. I'm going to change this to feet and when I do, you might think that the length of this line changes; it does not. You see, AutoCAD only recognizes units. So this line still has a length of 1. It's just that now this one represents one foot. So whenever I'm working on a file, I can use whatever unit of measure is convenient for my drawing. That being said, there are some standards. If you are a civil engineer or a surveyor, your drawing will always be set such that your units represent feet. If you're an architect, your drawing will always be set such that your units represent inches. If you have any questions regarding what units you should be using, check with your CAD manager or with others who work in your industry to determine which units are common for your type of work.
Take a look just above the Units menu. This says Units to scale inserted content. This means that if I assign a unit of measure to my drawing, in this case feet, and a consultant that I'm working with is constructing a drawing in millimeters, if I was to insert his drawing into mine, AutoCAD will do the conversion for me. It'll scale his geometry such that it comes in proportionately sized in my file. Once we're finished selecting a unit of measure, we can then take a look at these two groups at the top. These guys represent how AutoCAD will report measurements to us if we query our geometry. Using the current settings, Auto CAD will report lengths using decimals to a precision to four decimal spaces. It will report angles using decimal degrees, and it will report them to the even degree.
Note that in both cases, I can set my precision all the way up to eight spaces to the right of the decimal. I'm going to change my angle precision to two decimal spaces. And then I'll click OK to dismiss this dialog box, and we'll try it out. I'm going to select this line, and then I'll come over to my Properties palette, which is anchored to my interface. If yours is not visible onscreen, you can press Ctrl+1 to toggle it's display. I will then grab the slider and drag it down to the bottom. And we can see the length of this line is given in decimals, to four decimal spaces. The angle is also given in decimal degrees to two spaces. When I'm finished checking this, I will move my cursor out into model space, let that palette collapse, and then I'll press Escape to deselect this object.
Let's return to the Units dialog box and look at some of the other options we have available. As far as angles are concerned, Decimal Degrees is by far the most popular choice. If I open the menu, you can see that we have additional options. If you are a surveyor, you might be interested in having your angles reported in degrees, minutes, seconds, or using surveyor units, where the compass direction is also included. If you have any questions about the other options in this menu, come down and click Help and AutoCAD will give you more information. With respect to length type, we also have additional options. By far, the most popular are the Decimal and Architectural. If you are an architect, you will always be using the Architectural option because it will report your lengths using fractional measurement. When it comes to the other less common choices, once again, come down and use the Help feature to get more information. Let's close this dialog box. And at this point, I'd like to open a couple finished drawings and take a look at the Units settings that we're used. To do that, I'll click the Open icon. And I'd like to open these first two drawings. I'll do that by clicking the first one and then I'll hold my Shift key and I'll select the second one. I will then come down and click Open to open both files in the interface. Now in my case, the billiard balls drawing ended up in front. If that did not occur on your machine, you can always press Ctrl+ Tab to cycle through all of your open drawings.
Just continue to press Ctrl+Tab until the billiard balls drawing is in front. Now a standard American billiard ball measures 57 millimeters in diameter. We can see that I have a dimension right here of 57. I'm going to select this circle, I'll come over to my Properties palette, and I can see right here that in fact this circle has a diameter of 57. So in this drawing, the units must represent millimeters. I'm going to press Escape and we'll verify that by opening the application menu, come down to Drawing Utilities, and I'll select Units. And we can see, yes, in fact, the units in this drawing are set to millimeters.
Let's close this. I'll close the drawing as well. I'm not going to save changes. In this file, I have a standard billiard table. The standard dimensions for a professional billiard table measure 108 inches long by 54 inches wide. As you can see, I have some dimensions in this file. I'm going to select this line that represents the length of the table. I'll open my Properties palette, I'll drag down to find the Length setting, and I can see that this line measures 108 units long.
So in this drawing, each unit must represent an inch. I'll press Escape. Once again, we'll verify that by visiting the Units dialog box, and yes, in fact, this drawing is set up as inches. Once again, I'll close the dialog box, and we'll close this drawing without saving. So, no matter what unit of measure you prefer to work in, whether it be inches, feet, millimeters, or something else entirely, it's nice to know that AutoCAD is flexible enough to allow you to work using the units of your choice.
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