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AutoCAD

Drawing Scales, Part 1: Practicing Our Scales (Learning Curve AutoCAD Tutorial)

31 Jan, 2008 By: Bill Fane

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AutoCAD 2008's annotative objects change everything, automatically.

It was a dark and stormy afternoon. It was raining. No, that is not quite true; it was raining. And the wind was blowing. Again, that was not quite true; the wind was blowing. Captain LearnCurve and his gorgeous wife had been at Autodesk University the week before and were now supposed to be enjoying a leisurely drive home up the California and Oregon coastal highways. It had been lovely until just north of Santa Cruz, when it began to rain and blow. They decided to give up on the coastal route and went inland up highways 101 and I-5, ending up in Woodburn, Oregon, for the night. The drive had been miserable, what with one-half an inch of rain per hour and 60 mph crosswinds.

When they turned on the TV news, however, they learned how lucky they were. The Oregon coast had been hit with even harder rain, winds gusting to more than 125 mph, and 70-foot waves. Roads were washed out, the power was off, and things were not going to get any better for several days.

The news also reported that I-5 was closed north of Portland, Oregon, due to flooding. The Captain had never seen a storm of such a large scale . . . that's it! This month's topic! Scales!

Twenty years ago, one of the very first "Learning Curve" columns covered the topic of how to set the scale of a drawing. The same topic was covered 10 years later. Working on the Decade principle, 2008 should be about the right time to cover it again. If nothing else, the Captain likes to operate on a regular routine. Besides, a recent addition to AutoCAD's capabilities has changed everything completely.

We Can Do This the Hard Way . . .
Drawing scale was a big issue in 1988, because not everyone had figured out that we should always draw everything full size and then tell the Plot command to shrink or expand accordingly. The problem is that text and dimension sizes, along with hatch pattern and noncontinuous linetype scaling, must be resized by the inverse of the plot scale to make things come out right. Details at other scales can be a real nuisance because they involve a compound scale factor.

Surprisingly, the same topic was still a hot issue in 1998, because by then paper space had come into existence. The theory then was that the only thing that should live in model space was a model of the object being drawn, and all documentation (such as notes, dimensions, borders, and title blocks) should live in paper space.

This greatly simplified things as far as setting scale factors goes. Text and dimensions could be set simply and directly to the desired size because paper space layouts could be plotted 1:1. The drawing scale came from the zoom ratio between paper space and the viewports through into model space.

This approach still had a couple of problems, however. For starters, hatch patterns still needed to be scaled appropriately.

The main problem, however, involved dimensions. Okay, there were several problems with dimensions.

Yes, we could use object snaps to reach through into model space when attaching the dimensions, and, yes, the dimensions could be set to show the correct value even though they were measuring through the paper space viewport (hint: go to the Fit tab of the Dimension Style Manager dialog box and turn on the Scale Dimensions to Layout radio button).

The first of two problems with dimensions was that paper space dimensions were not associative to their model space objects. If we changed or moved anything in the model, then the paper space dimensions weren't attached properly and showed the wrong value. Show me a drawing that has never been changed, and I'll show you one that is only a few minutes old.

The other problem was that the dimensions were not visible in model space when we were editing the model, which could make editing very difficult.

The transspatial dimensions that were introduced in AutoCAD 2002 largely solved the first problem, but the second problem remained.

. . . Or We Can Do It the Easy Way
AutoCAD 2008 introduced the new annotative objects, which I believe has finally solved the drawing scale and dimension location issue once and for all.

At first glance, annotative objects might appear to be a little intimidating because of the great variety of variants and options, but they actually are of the essence of simplicity.

Rather than trying to describe how they work, the easiest way is to jump right in and see for ourselves.

1. Start a new drawing, using the standard acad.dwt as the template.

2. Draw a circle approximately 20 units in diameter and a rectangle that is roughly 10 units square.

3. Apply a diameter dimension to the circle and a linear dimension to the rectangle. Now you see the basic problem with drawing scales. The dimensions are so small that they are almost invisible. In the past, we would have had to calculate a suitable scale factor and then would have adjusted the overall scale factor on the Fit tab of the Dimension Style Manager accordingly.

4. As I have been hinting, there is an easier way now. Select Format | Dimension Style to invoke the Dimension Style Manager dialog box.

The Annotation Scale drop-down list is used to set the drawing scale in model space.

5. Change the current dimension style from Standard to Annotative. The triangle icon is used throughout AutoCAD 2008 to indicate annotative. It is meant to show the end of a triangular engineer's scale. Click Close.

6. Look in the lower-right corner of the AutoCAD window and note the annotation scale item with the value 1:1 and the inverted triangle beside it. Click on the triangle to display the scale drop-down list. Okay, so it doesn't really drop but instead pops up due to its position on the screen, but you know what I mean. Select the 1:10 item from the list.

7. Make sure the Annotation Visibility button is on and the Automatically Add Scales button is off.

8. Now apply a diameter dimension to the circle. Magic! It automatically sizes itself to suit the drawing scale!

9. Go back to the Annotation Scale drop-down list and set the scale to 1:5.

10. Apply a linear dimension to the rectangle. As we saw before, it sizes itself correctly for the selected scale. Note that its size is different from the diameter dimension, but both dimensions show the correct value.

11. Now switch to paper space Layout 1. By default, it will have one viewport that pretty much fills the sheet, and your model space objects should be visible within it. If they are not visible, double-click inside the viewport to enter model space and then pan and zoom appropriately. When you are finished, move the cursor outside of the viewport boundary and double-click anywhere in the paper space layout to return to paper space.

12. Click on the viewport boundary and select 1:10 from the drop-down list beside the VP Scale item that appears in the lower-right corner of the AutoCAD screen. The contents of the viewport scale accordingly, and only the dimension on the rectangle is visible. The dimension is scaled properly.

13. Click on the viewport boundary and select 1:5 from the VP Scale drop-down list. The viewport scales itself accordingly, and only the dimension on the circle is visible and scaled properly.

14. Click on the viewport boundary yet again and set the VP scale to 1:16. The viewport scales itself, but now neither dimension is visible. Do you see a pattern developing here? A viewport only displays those dimensions whose model space scales at the time of their creation matches the current viewport scale.

15. Resize the viewport to approximately one-half its size. The easy way to do this step is to select it and then grip edit it.

16. Use the Vports command (View | Viewports | 1 Viewport) to create a second viewport.

17. Set one viewport scale to 1:10 and the other to 1:5.

18. Double-click inside the 1:10 viewport and pan until the circle and its dimension are nicely framed.

19. Double-click inside the 1:5 viewport and pan until the rectangle and its dimension are nicely framed.

20. Double-click in an open area of the layout to return to paper space. If you zoomed at all while you were in model space through a viewport, then you will have to reset the viewport scale.

Bingo! We now have two details at two different scales, and we didn't need to do any calculations or switching of dimension styles. Everything was drawn full size and was dimensioned in model space. Better yet, any changes in model space automatically reflect through to the paper space layout. Go ahead, give it a try!

Annotative self-scaling dimensions may seem complex, particularly because we took 20 steps to get here, but the basic procedure really requires only four steps:

1. Create an annotative dimension style or change an existing one to annotative. To do this, simply go to the Fit tab of the Dimension Style Manager and click the Annotative check box.

2. Set the desired drawing scale from the Model Space Scale drop-down list.

3. Apply suitable dimensions.

4. Go to the paper space layout and use the VP Scale drop-down list to set the viewport scale.

That's it!

Be sure to come back next month when I will discuss annotations with multiple scales other types of annotative objects including text, Mtext, attributes, blocks, and hatch patterns.

And Now for Something Completely Different . . .
If you really like seafood, go looking for a buffet dinner at a casino in Laughlin, Nevada, on a Friday night. For some reason Friday seems to be Seafood Night at almost every casino. The only exception we could find offered a very mediocre, overpriced buffet.