Join Scott Onstott for an in-depth discussion in this video Creating linear dimensions and adjusting their properties, part of AutoCAD: Working with Dimensions.
- Open the Dimensioning01 exercise file. It contains a 3D model of a sextant that I designed. I've used this model in another course in the library called documenting AutoCAD 3D Models. In that course, we generated these two layouts, S1 and S2, that have different views of the model. Go to S2, and this is what we will be dimensioning in this course. Zoom in on the frame detail up here.
And notice that when you move the cursor over it, the whole thing highlights. This is a drawing view, which is a projection of the object in model space. We can dimension this just like we could if we were looking at a view port. In fact, S1 has viewports that display the geometry. Although it's technically possible to dimension objects in model space, it's recommended that you don't do that. The system is optimized for dimensioning in a layout.
So let's go back to S2, and notice how when I move the cursor over these views, they highlight. That's fine, when we're creating and laying out the views, but now that I want to dimension, I think this is a bit distracting, so let's go into Options. Go to the Selection tab, and in this preview area, uncheck Selection preview When no command is active. We don't want to see that. Now if we're not using a command and I'm just moving the cursor over the screen, then these objects don't highlight.
Let's zoom in up here in this area and begin to add some dimensions. You can find the dimension tools on this drop-down menu. You can also find them on the Annotate tab, in this drop-down menu. It's really the same difference. Click Linear and the prompt says, "Specify first extension line origin." Make sure you have Object Snap on, and turn on Endpoint, Midpoint, Center, Perpendicular, and let's not have Tangent on.
Let's also turn on Intersection. Sometimes that is helpful. Now, we need to specify the first extension line origin. That's going to be right here, at this endpoint. Now it says, "Specify second extension line origin." That would be at this endpoint. Now we have a dimension attached to the cursor, but we need to specify the dimension line location by clicking a point. That completes the command.
So the anatomy of the dimension includes extension lines and the dimension line. There are also arrowheads and text, of course. Once you've created a dimension object, you can click on it and you'll see a bunch of grips. The grips allow you to adjust the position of the dimension line and you can also change where the extension lines are connecting to. So if I move this extension line grip down here, the value updates. But here I also get an exclamation point symbol, which means that it's not associated properly.
I'll click on that, and choose Reassociate. It prompts me to specify the first extension line origin and then the second one again. Now that it's associated, it means that if I were to change the 3D model in model space, it would automatically update the dimension here in the layout. That's something that we'll experiment with later. Let's go ahead and make another linear dimension over here. From this endpoint to this endpoint.
I'll click a point over here. As you see, you can make horizontal or vertical dimensions with the linear tool. The drawing units are centimeters. We have numbers here which are way more accurate than we can manufacture this object. We can't really specify the 10,000th of a centimeter here and get away with it. So we should decrease the precision of our dimensions.
I'm going to select both linear objects and type P R Enter for properties. Scroll down and you'll see a really long list of properties associated with these objects. Let's locate Precision down here under Primary Units at the bottom of that section. Click here and change this to 0.0 so were going to say that we're accurate to the nearest millimeter, which is a tenth of a centimeter, of course.
So press Escape to deselect.
- Creating different styles of dimensions: linear, baseline, etc.
- Editing dimension styles
- Specifying tolerance
- Re-associating dimensions
- Editing dimensions text
- Labeling with multileaders