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e-vol. 85, Spring 2010

by Kendred Cooper,
MCAD Solutions Engineer


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AutoCAD® 2010 Can Constrain You…
Part 1 of 2

With the introduction of the 2010 version of AutoCAD®, Autodesk decided to take some tools from their flagship 3D mechanical design package, Autodesk Inventor, and bless AutoCAD with some of those same tools.  The two tools that I’ll be covering are geometric constraints & parametric dimensions.  In this edition, we’ll cover the geometric constraint tools.  As this article will be a two-part article, we will cover the parametric controls in the next newsletter edition.
           
OK, I know what you’re thinking: What in the world are constraints?  Well, a constraint simply identifies and controls the behavior of object A as it relates to object B.  Think of 2 parallel lines. In typical AutoCAD, there are no controls that maintain this parallel behavior between them.  Enter the Parallel Constraint control and those lines will remain parallel until said constraint is deleted.  Constraints function like OSNAP’s on steroids because constraints maintain that behavior, whereas OSNAP’s are an initial control when creating or editing object relationships.  An OSNAP doesn’t “stick” after you create the object in AutoCAD and you can then move or change the object(s) regardless of the OSNAP you used to create the object(s).
 
Now that the Webster portion is over, how do constraints work in AutoCAD?  See the video link as a reference (http://www.mcadusers.com/).  You have different ways that constraints can affect geometry.  Constraints can be applied to either an entire object or to a point on the object.  Using the ORTHO option, you can draw a line to be horizontal or vertical, however, once completed, you can then modify the lines angle.  Applying a Horizontal or Vertical constraint to a line object will prevent the angle of the line from being changed.  You can also apply a horizontal or vertical constraint to an endpoint of the line and another point of another object.  Doing so will bring those points into horizontal (or vertical if you used that one) alignment with each other.
 
All of the constraint controls for AutoCAD can be found on the Parametric tab of the ribbon interface.  As for those who use the classic interface view, look under the Parametric menu or simply turn on the Parametric toolbar.
 


Ribbon Tab
 


Classic Toolbar
 
 
The benefit of constraints can be best realized when working on a drawing with multiple views of the same 2D geometry.  The thickness of the object, represented in the Front View, can be set to match the thickness lines in the Side (End) View.  Any Holes represented in the Top View can be set tangent to the hidden line representations in the Front View.  These controls can be applied to any orthographic view projection (such as Front to Right and Top to Front).  For Top to Side representations you “could” use construction lines to setup the controls, however, the Parametric controls (see article in the next newsletter edition) will better fit this need.
 
To see constraints that have been applied, there is a Show Constraints command. Starting the command and selecting the geometry will bring up the glyph box listing the constraints for that object.  Should a constraint no longer be needed, select the constraint glyph and then right-click and delete it to remove that control.  All constraints for every object can be shown using the Show All command. However, you’ll soon realize that with that many objects and that many constraints, the modeling area is very cluttered.  Since there is a Show All command, the Hide All conveniently removes the display of all constraint glyphs for drawing clarity.
 


Clutter when viewing all constraints
 
With constraints, yes, there is some up-front work that needs to be done.  This up-front work may add a few minutes to your design time but the benefit of using constraints far out weighs the drawbacks of a few minutes added time.  None of us ever hope to make changes to a design, but it’s typically a necessary evil in the design process.  Making changes to a design can sometimes take more time than initially creating the design took.  AutoCAD constraints bring part of the tools needed for a “change it once, change it everywhere” 2D CAD workflow.  Applying object constraints can dramatically decrease editing times of your drawings.  In our next newsletter, we’ll look at Parametric Dimensions and how these work alongside object constraints to complete that toolset for the “change it once, change it everywhere” workflow.

 

This page last edited on Tuesday, June 08, 2010