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Speling, Dougr, others Thanks. 1 more Favor


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Speling, Dougr, Steve, gggg.., David Martin, Mike, rcamp and brain_Adkins.

I was surprised to see the kind of responce I got from all of you in the post Good modeling Practice, Thanks so much for the reply.

I have one more hurdle in assy probabally which you guys can solve, its top down design.

I have done a couple of them but I am not confident that they are correct. Can you guys tell me how you approach a top down design, how you start it and how you progress?


New member
Good question. Not a simple question to answer, because this involves a lot of information. You can start off an assembly with TDD, or apply TDD principles when you find your assembly getting too complicated to manage with the traditional Bottum-Up approach.

Here are the basic steps in Pro E:

1. Create a layout, in which you document any important information for your assembly. Rough sketches, notes, and balloons are often placed, but the most important stuff are dimensions, parameters, and relations that affect multiple components.

2. Define your basic assembly structure. Create the assembly, and within the assembly create your subassemblies, and components. Use the include functionality to add off-the-shelf components.

3. Create an assembly skeleton. Skeletons have multiple purposes; they'll be the frameworks of your assembly. Most important uses: all components will be assembled to the skeleton (to reduce parent-child relationships), and any important geometry used by multiple components will be consolidated in the skeleton model. They are also often used for space claims.

4. Communicate your design information. Link your skeletons, assemblies, and parts to your layouts by declaring them to the layout. Use Data Sharing features (Copy Geoms, Shrinkwrap, etc.) to communicate geometry from the skeletons to your individual models.

5. Create your part geometry and populate the remaining components in the assembly (e.g., assemble, package, include, pattern, copy, bulk items, UDF's, repeat, etc.).

6. Manage external references and interdependencies by using the Global Reference Viewer to investigate, Reference Control to establish limits, and traditional techniques (i.e., redefine) to break unwanted interdependencies.

That, in a nutshell, is Top Down Design. There's more to it, but that's the basics. Note that you continually revisit the steps in and out of order throughout the design process.

David Martin

Torgon Industries


New member
I should have said this first:

The whole point of TDD is to make your assembly as parametric and associative as possible to facilitate redesigns. It's more work up front, but saves you a lot of time later on. I've seen cases where major assembly changes that required weeks of work using bottum-up approaches are reduced to minutes and hours with TDD, because you are no longer making changes to each individual part model.

When you need to make changes to dimensions and parameters, you update the layout. When you need to make changes to geometry, you change the skeleton. (If your assembly is extremely complicated, you may want to have multiple skeletons; one for assembly constraints, one for shared geometry and component interfaces [typically for enclosures and complex surfaces]; one for space claims; one for space claims; and one for mechanisms.) The amount of detail and information you document in your layouts and skeletons depends on the complexity of the design and how much you want or can control at the assembly level.

And some companies choose to skip the layout and document the important dimensions, parameters, and relations in the skeleton. Again, the choice is up to you.

TDD allows for better control and management of complex assembly designs.

David Martin

Torgon Industries


New member
OK, as long as this thread is in the Rant-n-Rave forum I let fly with my rant and see what suggestions you folks have.

All of the PTC training classes teach as if you have the full blown advanced assembly module. I'm just guessing but I'd bet the majority of new seats sold are of some flavor cooresponding to the old Foundation and Foundation II package. That means that you can't use most of the techniques PTC advocates.

What can poor boy do; 'cept sing in a Rock & Roll band?



New member
I've thought about that too; without AAX, most of TDD is unavailable.

And it used to be that everything taught in the Introduction to Pro class only required the Foundation. But that changed a couple years ago. For a brief while, ISDX and BMX were taught in Intro, but wisely PTC killed that. From what I know, there's information in the basic Wildfire class (called Fast Track) that requires additional extensions.

Layouts must have AAX. But a lot of companies implement TDD without layouts.

If Copy Geoms and Component > Adv Utils > Merge are available in the Foundation-- I don't know, it'd be nice if someone could verify this-- then conceivably someone could fake a skeleton with a part model. (Just be sure not to include any solid geometry in the fake skeleton; otherwise your assembly mass properties would be incorrect. And don't forget to filter the fake skel from your BOM's.) And that way one could get around some of the limitations of not having AAX.


New member
There is one thing that I hate about layouts, but I think there is a way to get over it... just that i do not know !!

The inheritance in layouts are one way... If i want to change a dimension, I have to do it in the layout... I cannot edit it in the skeleton... Pro/E gets back saying "dimension governed by relation <model dim> = <layout param>"

The point is I am trying to edit that layout param itself, and it is difficult to fine tune something on a layout, come back, regen and take a look... If anybody has any ideas on this please reply, PM me, email me, call me, fax me... anything... just let me know !!

I am open to ideas, as long as I can edit my dimensions from the skeleton and the layout... I can try any of your ideas if you think its worth YOUR time.

Thank you...


New member
You can fake skeletons pretty effectively using simplified reps. Just create a rep. called 'NO_SKEL' (or whatever) and exclude your skeleton model.

As to the mass properties; if you create your skeleton using surfaces, it should not affect your mass analysis...