Dimension Tips (Circles and Lines AutoCAD Tutorial)

30 Nov, 2008 By: Lynn Allen

Two features found in AutoCAD 2008 can tame your misbehaving dimensions.

As I was traveling and sharing a variety of AutoCAD tips recently, I found two very cool key dimensioning features in AutoCAD 2008 that somehow sailed in under the radar, and it’s about time the word got out!

It is a rare application that doesn’t deal with some type of dimensioning. Over the years we have come up with so many clever means of getting the final dimensions we need for the perfectly drafted design. We have learned the advantages of associative dimensions and the disadvantages of dealing with them after they’ve been exploded.

The Dimbreak Command
The first dimensioning tool, Dimbreak, takes us one step closer to getting our picture-perfect dimensions without risking the wrath of our drafting instructors. Figure 1 shows a typical case of crossing dimensions. In the past we might have exploded a dimension, followed with a break to follow proper dimension standards. The Dimbreak command was added to AutoCAD to avoid just such a situation, and its intelligent-breaking facility continues even when the dimension is moved.

Figure 1. Crossed dimension lines are not acceptable in most applications.

The Dimbreak command is simple. Select the dimension line you wish to break, and then select the dimension(s) or objects that the dimension line crosses.

Figure 2. Use the Dimbreak command to break a dimension without exploding it. The great thing about the Dimbreak command is that the broken dimension is smart enough to reheal itself should it be moved to a location that no longer crosses the originally selected objects.

The great thing about the Dimbreak command is that the broken dimension is smart enough to reheal itself should it be moved to a location that no longer crosses the originally selected objects.

Figure 3. A dimension line that is broken by DIMBREAK can reheal itself if needed.

And if I move the broken dimension line somewhere where the break needs to be modified, DIMBREAK is smart enough to sort that as well.

Figure 4. Dimbreak recalculates the break when necessary.

Let’s take a look at Dimbreak step by step:
   Command: Dimbreak
   Select dimension to add/remove break or [Multiple]:
   Select object to break dimension or [Auto/Manual/Remove] <Auto>:
   Select object to break dimension:
   1 object modified
The same process is used should you need to remove a break from a dimension. If for some reason you can’t get the exact break that you want, a handy manual option lets you decide where the break should go. However, if you manually break a dimension, it won’t be smart enough to automatically update should you move the dimension.
Dimbreak works on the following object types:

  • linear dimensions (aligned and rotated)
  • angular dimensions (2- and 3-point)
  • radial dimensions (radius, diameter, and jogged)
  • arc length dimensions
  • ordinate dimensions
  • straight multileaders

Unfortunately the following dimension and leader objects do NOT support dimension breaks:

  • splined multileaders
  • “legacy” leaders (You are expected to use the new multileaders for leader dimensions.)

A few obvious situations also do not support the Dimbreak command. If you have a dimension that is part of a block or xref, Dimbreak won’t break it. You can, however, use objects within the xref or block as cutting edges to break a dimension. Dimbreak won’t let you place a break on an arrowhead or dimension text (which you wouldn’t want anyway). Last, both the dimension you wish to break and the object it crosses have to be in the same space (paper space or model space). You could, however, use the manual option to get the desired result.

If you want to control the size of the automatic break, you can do so under the Symbols and Arrows tab in the Dimstyle command.

Figure 5. Use the Dimstyle command to control the automatic break size.

The Dimspace Command
Let’s move on to another favorite:  the Dimspace command.

For years we have manually moved baseline dimensions to space them evenly. Of course, we typically guestimated the spacing, moving them until they looked good enough to the naked eye. The Dimspace command takes the guesswork out of evenly spacing our dimensions and gets the job done quickly as well.

Figure 6. Unevenly spaced baseline dimensions can cause us grief.

Rather than grabbing each of the dimensions and tugging at them until they look OK, you can use the Dimspace command. Dimspace can be used on linear or angular dimensions.
   Command: Dimspace
   Select base dimension: in most cases the dimension line closest to the part.
   Select dimensions to space: select those dimensions (other than the base dimension) you want to evenly space.
   Select dimensions to space:
   Enter value or [Auto] <Auto>: input a specific distance or use Auto for AutoCAD to determine the proper spacing.

Figure 7. In ourexample, the base dimension is the one nearest to the part.

Figure 8 displays the result of Dimspace for our example.

Figure 8. The resulting spacing is perfectly even!

If you choose the Auto option, AutoCAD will multiply the text height of the base dimension by two to determine the spacing. I noticed the Help file indicated that the selected dimensions must share an extension line for Dimspace to work — definitely not the case as you can see in my examples.

You can also use Dimspace to align linear and angular dimensions end to end by using a spacing value of 0. That means if someone has moved your continued dimensions so they no longer line up, you can use Dimspace to straighten them!

Figure 9. Uneven continued dimensions can be tricky to even out perfectly. Click the image for a larger view.


Figure 10. A spacing of 0 evens up the continued dimensions. Click the image for a larger view.

Give these two dimension tools a try on pesky misbehaving dimensions. You might just find yourself with a few extra minutes on your hands. Until next month, happy AutoCADing!

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