{"id":9086,"date":"2019-05-23T07:00:00","date_gmt":"2019-05-23T14:00:00","guid":{"rendered":"https:\/\/www.autodesk.com/blogs\/autocad\/?p=9086"},"modified":"2020-04-08T09:36:17","modified_gmt":"2020-04-08T16:36:17","slug":"real-world-example-of-using-2d-constraints-in-autocad","status":"publish","type":"post","link":"https:\/\/www.autodesk.com/blogs\/autocad\/real-world-example-of-using-2d-constraints-in-autocad\/","title":{"rendered":"Real-World Example of Using 2D Constraints in AutoCAD"},"content":{"rendered":"

AutoCAD has had 2D geometric and dimensional constraints for a while, but most drafters don\u2019t leverage their functionality in everyday use. I sometimes think it is because they can\u2019t think of an everyday use for them. In this post, let\u2019s look at a real-world example of using constraints that really saves you a good bit of time and automates a workflow that aids you in designing. (And be sure to check out my Tuesday<\/a> Tips<\/a> article<\/a> with an overview of 2D constraints.)<\/p>\n

Borehole Construction<\/h2>\n

The specific example I will cover here is for constructing utilities under a major road or highway where we cannot dig a trench due to the high volume of traffic on the road. Instead, we will propose borehole construction which will dig a hole underneath the road using a casing pipe that will carry the utility pipe. The diagram below shows the design standards that we must follow for this project<\/p>\n

\"AutoCAD<\/p>\n

So, looking at the diagram, we can see that the standards call for a range of deflection angles for the entrance and exit of the pipe. Note though that the entrance and exit can be swapped based upon the existing conditions on either side of the road. Now, in an \u201corthogonal\u201d world, this wouldn\u2019t be that difficult as you could simply have a block that has these deflection angles. But, in the real world, the existing ground will vary, the depth to the pipe will need to be adjusted, and the deflection angle will need to follow this adjustment. 2D geometric and dimensional constraints to the rescue.<\/p>\n

Drawing the Criteria<\/h2>\n

Below is our area of design. I have a profile view (cut with Civil<\/a> 3D<\/a>) at a scale of 1:1 so that we can design this without having to worry about an exaggerated scale.<\/p>\n

\"Profile
\nThe first thing I\u2019ll do is to draw the basic geometric components as it really doesn’t matter how they are initially drawn because the constraints will \u201cfix\u201d the geometry for me.<\/p>\n

\"geometry<\/p>\n

Use the AUTOCONSTRAIN tool to automatically constrain the geometry.<\/p>\n

\"AUTOCONSTRAIN\"<\/p>\n

Now since I don\u2019t always have \u201cflat\u201d ground, I\u2019m going to delete the horizontal and perpendicular constraints.<\/p>\n

\"horizontal<\/p>\n

To finalize the geometric constraints, I will add a vertical constraint to one of the vertical lines as there is already a parallel constraint associated to the two lines.<\/p>\n

\"\" Now, we will need to add the geometric constraints to add the appropriate angle of deflection on either side. Navigate to the Dimensional panel in the Parametric tab and add an angular dimensional constraint.<\/p>\n

\"\"<\/p>\n

Now, you want to select the vertical line first and then the adjacent line, and define an angle of 78 (90-12).<\/p>\n

\"Constraints<\/p>\n

And add one to the other side for a value of 82 (90-8).<\/p>\n

\"\"<\/p>\n

Now, we can position our lines to the correct location in the profile to see where the entrance and exit pipes will go. Some little tricks to working with the geometry are listed below:<\/p>\n