CAD Software CAD programs: What does "parametric" mean in the context of CAD?

[MetricRocketeer]

Hi TRF colleagues,

I have this question pertaining to CAD, please.

In the context of CAD programs, what does it mean to say that a particular program is parametric? We have all seen this nomenclature when reading about CAD programs. If you go to the Wikipedia article where CAD programs are compared — https://en.wikipedia.org/wiki/Comparison_of_computer-aided_design_software — you will see the term throughout. We don't have to go to Wikipedia, though — you see the word everywhere when referring to CAD programs.

Are there CAD programs that are non-parametric? If so, then what does a parametric CAD program do that a non-parametric CAD program cannot do?

Thank you.

Stanley

 

[Kelly]

Not an expert here, but:
Non-parametric (direct) is basically you draw what you want, and wysiwyg.
Parametric design is more numbers(parameters)-based: This part is 'x' mm wide, this hole in it needs to be 1/4 the size of 'x', that other hole always needs to be M6. Now I can set 'X' to be anything I want, and still get a part that meets my needs. You can define parts that meet a constraint (like, this shaft always needs to fit into that hole, with a clearance of 'y', or that part always needs to be big enough to span the distance from part 1 to part 2, etc.)

 

[John Kemker]

From my understanding, "parametric" indicates that the drawing is either based on parameters, or the parameters can be changed in order to change the drawing.

 

[OzHybrid]

Parametric is where you change one thing and EVERYTHING that is associated with it is also changed. A good example is the drafting done in OpenRocket. where if you change the nosecone length, the actual shape changes too. The mathematical definition of the shape is the same, but the position of every point between the start and end of the nosecone is different.

In SCAD you can define let's say a stack of cans by defining 2 cans completely with their locations in space defined separately where one is on top of the other. This is NOT parametric
If I define the overall height of the stack and define the height of Can 1, then the height of the Can 2 is a parameter of the overall height and the height of Can 1. The design is parametric. At least partially.
I hope this clarifies what parametric design is. The definition gets lost by the number of objects you find on thingiverse where they call the design parametric but it's not. At least not using the files they upload. An example of that would be if I used my FinCan scad design program to create a fincan uploaded only the STL file and called it a parametric fin can. It's not parametric as far as the user is concerned unless I upload the parametric fin can program I created in SCAD too.
Hope that clears things up.
Norm

 

[Rschub]

Parametric CAD has parameters that you can assign a value to, that define the shape. The parameters can be changed and linked to other parameters, allowing quick changes throughout the model by changing a few numbers. Most companies have moved to some type of parametric software for their CAD, there are many varieties.
Non parametric CAD creates shapes. That's it. We in the engineering world call that art.
I realize some may disagree, and that's ok. The world needs artists too.

Edit: Parametric CAD has something called a history tree, where you can go back and change things if you need or change the design direction, without completely redoing your work.
Non parametric CAD is like:
The Moving Finger writes; and, having writ, Moves on: not all thy Piety nor Wit Shall lure it back to cancel half a Line, Nor all thy Tears wash out a Word of it.

 

[Scrapmaster87]

In non-parametric CAD, you're just placing lines, curves, etc to build your model/ representation. Which you better have most of your calculations done already because it's a pain to go back and fix stuff.

In parametric CAD, you start with a sloppy sketch and then define it's shape via parameters. This is actually the fastest way to get things done, blast a shape down and give it dimensions. You can define some parameters via a formula, with live measurements in the model as inputs too! More advanced would be a design table: a series of input values to automatically generate the geometry of variants of a common design. Further down this road is linking outputs from external programs to build your designs (drawings too)!

Parametric modeling/CAD is a mind-bogglingly powerful tool. It's only disadvantage is the significant processing horsepower requirement vs similar work in non-parametric. I use both at work, non-parametric (Auto-CAD) for electrical drawings and plant layouts (lots of small details), and parametric (Creo) for 3D/mechanical/tooling work.

 

[asm109]

A parametric modeler, has the history tree. This is a list of each modelling step you have taken as you create your model.
The order of the steps is important, If you were to delete or change one of the early steps, the later steps might be deleted or at least changed.
Fusion 360, Solidworks, Creo are all examples of a parametric modeler.

Creo also has a non parametric modeler, called Creo Direct. Most have never heard of it. It was originally created by Hewlett Packard and called One space designer. I used it ALOT and I really like it.
The model is allways the way it is and you can modify it by adding or subtacting features. Or modifing a face by moving it or aligning it to a face in another part. When you are done the model is just there ready for more changes. The order that you create things are irrelevant. When you are what iffing a design where you have no idea what the finish line looks like it is fantastic.

 

[MetricRocketeer]

I want to thank all of my TRF colleagues for helping me understand this issue better than I have ever understood it before.

I am following up with a thread that I am about to post in the same forum, which I will entitle "Parametric CAD programs and parametric equations".