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Understanding Dimensional Constraint

December 6, 2009 in AutoCAD, CAD, Revit

parametric tab
Another parametric feature available is dimensional constraint. We discussed about geometric constraint, and this time dimensional constraint.

Dimensional Constraint Types

Basically we use dimensional constraint to maintain distance between points or objects. Usually dimensional constraint don’t work alone. We use geometric constraint along with dimensional constraint.
There are three types of dimensional constraint:

  1. Dynamic Constraint
  2. Annotational Dimension
  3. Reference Constraint

Annotational Dimension

In a nut shell, annotational constraint behave like common dimension we know all these years. You can plot it, you can assign it on a layer, and the size behave like other annotation. The size is not affected when you zoom the drawing.

Dynamic Constraint

Dynamic constraint is a bit different. it’s only for display purpose. It will not be printed. If you remember how you use parameter in dynamic block, it also display at the same size when you zoom the drawing.
You can change the form, dynamic or annotational by changing the ‘form’ variable.

Command:
DIMCONSTRAINT
Current settings:  Constraint form = Dynamic
Select associative dimension to convert or
[LInear/Horizontal/Vertical/Aligned/ANgular/Radial/Diameter/Form] <LInear>:F
Enter constraint form [Annotational/Dynamic] <Dynamic>: A

Reference constraint

Reference constraint is not created directly. You can create a dynamic or annotational dimension, and then convert it to reference dimension.
reference dimension
We use reference constraint only for showing the distance values. We can’t change the parameter like dynamic or annotational constraint. Let’s compare them.
Annotation constraint size will follow the object size when you zoom. Dynamic constraint will show the same size, no matter how you zoom it. The reference dimension is shown with brackets.
dimensional constraint type

Using Dimensional Constraint

After you placed dimensional constraint, you will see the parameter name like d1, d2… dia1, dia2… by default. We can change it later. You can change the parameter by selecting the constraint, right click your mouse above dimension, and select edit constraint.
Or you can change the name and value in properties palette.
constraint properties
We can input calculation in expression field. For example, we want the base length is dependant to body length plus 20mm clearance. This workflow is used heavily in manufacturing design.
By using dimensional constraint, we don’t modify the object. We change the parameter value, and the object will be adjusted. To make the result predictable, we use it together with geometric constraint. We will create some objects using these parametric behavior later. But that’s the concept.
As I don’t write too much details in this parametric feature, you can also read them in my friend blog, Orhan Toker:

  1. Geometric Constraint (1)
  2. Geometric Constraint (2)
  3. Dimensional Constraint (1)
  4. Dimensional Constraint (2)

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Source: CAD Notes – Understanding Dimensional Constraint
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Understanding Geometric Constraint

December 6, 2009 in AutoCAD, CAD, Revit

parametric features
Finally, Autodesk add parametric features in AutoCAD 2010. Why finally? This feature is already there in manufacturing industry for decades. If you have used any manufacturing application like Inventor, CATIA, SolidWorks, ProE, etc, then you should be already familiar with this feature.
There are 3 panels in parametric tab: geometric, dimensional, and manage. Let’s talk about geometric first.
Geometric constraint will maintain how your objects related to each other. Let’s see this example.
Let’s say we have a rectangle. We know that the sides have to be perpendicular to each other. But sometimes during the design, you may need to change it. If I stretch one of the rectangle vertex, then it would not be a rectangle anymore. AutoCAD doesn’t know that you want to keep it as a rectangle.
stretch vertex

We can prevent this by telling AutoCAD that we want them always perpendicular to each other. We can add perpendicular constraint. So I add a perpendicular constraint to the two sides. I try to stretch the vertex again.
1 perpendicular constraint
As you can see, the two sides are kept to be perpendicular to each other. But the other edges don’t. We have to add all constraint to keep it a rectangular.
all perpendicular
That’s the concept.
I don’t know if this gives many advantages to AEC industy or or. I know that MicroStation has this feature years ago, but it’s not become a popular feature. Maybe because Bentley Systems doesn’t have solutions in manufacturing industry.
There are some use that I can think of: in dynamic block. But I’m not sure if we can use it extensively in drafting. I saw the example in new features workshop, the sample is for manufacturing, not AEC. Do you have any idea, where we can use it in AEC industry? I will try to post some dynamic blocks using this parametric feature, and maybe you can suggest me how we can use it in drawings.

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Source: CAD Notes – Understanding Geometric Constraint
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Direct Versus History Based Modeling

November 7, 2009 in CAD, Kubotek

 This is an article written by John Groener of Edge Data.  He is a reseller of both AutoDesk and Kubotek CAD software.  I hope you enjoy his perspective and find it informative and educational.  His contact information follows.

Direct
Versus History-Based Modeling

In 1985 History-Based Modeling was implemented in Pro/Engineer® and quickly
imitated by several “Me-Too” CAD products such as CATIA®, SDRC IDEAS®, and
UniGraphics®. Then came the “Mini-Me-Toos” such as SolidEdge®, SolidWorks®,
IronCAD®, and Inventor®.

History-Based modelers require the CAD user to define parameters and
constraints when designing a part. The parameters provide relationships to
other features in the 3D part, and constraints allow that part to be
constructed unambigously.These parameters, features, and constraints are stored
in the order they were built in the history tree and must be accessed through
that tree to be changed.

History-Based Modelers have shortcomings.
 •    Engineering changes can be a difficult, painful
process. A new user has to decipher and untangle the history tree so that he
can make changes.
 •    Each CAD software package has its own proprietary
file format so parts are not easily interchangeable.
 •    Assemblies can be time consuming to set up and
manipulate.
•    There is no stand-alone 2D drawing capability.
•    Surface models are not easily interchanged with solids.

KeyCreator uses Direct Modeling to create and edit 3D Models. NO
user-defined history tree is needed. Why? Because KeyCreator creates the
feature tree and KeyCreator allows direct dimension driven editing.  In
other words parametric, feature-based editing of all geometry.

KeyCreator has Comprehensive 2D drafting. KeyCreator produces complete
2D drawing sheets associated to the 3D model. KeyCreator uses levels (aka
layers) to manage 2D information, so 2D drafting can be standaone if desired.

KeyCreator Reads Native CAD Files from other CAD software like Pro/E,
Solidworks, Unigraphics, CATIA, Parasolids, ACIS, STEP, IGES. No fixing, no
healing, just read it in, edit, and GO!   Wait … how about the
parametrics? That’s KeyCreator’s job. No need to use the import as reference
geometry and re-parameterize it. Just go to work.

KeyCreator incorporates surface modeling. With KeyCreator you can create
a free-form surface model and then convert it to a solid model to facilitate
operations like shelling and fillets. Excellent healing tools insure that the
part is completely contiguous and accurate. KeyCreator is therefore a TRUE
Hybrid Modeler (a hybrid of solid and surface models).

KeyCreator’s assembly modeling features can manage all data in a single
file. It does this by using level management – that same invaluable 2D tool
which is noticeably absent in the other Solid Modelers. For very large
assemblies, KeyCreator can export parts in the assembly to multiple part files
and then reference those parts as entities.

KeyCreator is a complete Mechanical CAD solution with a unique ability to read
any CAD data format and then easily manipulate geometry, making it an
invaluable resource for any engineering design and manufacturing application.

KeyCreator and Edge Data

Did you know that …
… KeyCreator®, formerly known as CADKey®,  was introduced in 1984 as a CAD
Package with 3D Digitizing capabilities.

… Kubotek Corporation purchased CADKey in 2003, renamed the software
KeyCreator, invested heavily in R&D, added advanced 3D, CAM, and universal
CAD translation.

… Edge Data, one of the first AutoCAD dealers in the country, has been
providing New England with CAD products and training since 1983
…Today Edge Data is an Authorized Kubotek Service Center, and provides CAD
training for KeyCreator and other software.

John Groener
Edge Data Corp.
authorized kubotek service center

www.edgedata.com

978-537-9800
john@edgedata.com

Source: CAD Freedom and Precision – Views and News from KubotekUSA – Direct Versus History Based Modeling
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