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Sketches and references based on assembled parts: Good or Bad idea?

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Sketches and references based on assembled parts: Good or Bad idea?

There have been several times, when I come to a dead end, that I design parts' features based on assembly file.

For example, if part A has a peculiar curve or section, I fisrt assemble that part B , put it strongly into placement and then I activate it and using part A lines as references, I sketch my details on Part B.

The simplest example coming into mind... I had recently an extrude feature on a assembled part. I went to assembly, activated that part and edited the extrude up to a surface of another part. Is there any chance that I have problem with regenerating later on?

In general, Is it a good or bad idea and what might be the cons!?

8 REPLIES 8
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Re: Sketches and references based on assembled parts: Good or Bad idea?

This is top-down assembly methodology. It can be done reliably and a lot of groups do it. It will get you into trouble from time to time and you will have to track down the problem.

Some organizations will not let you use this methodology. It doesn't play nice with some established systems. You are building dependencies across parts and you now have to maintain both of them.

As long as you are aware of the spider web you are creating, you will be fine... but use it for the right reasons. Do not use it as a crutch to simply make modeling easier... use it because you need the associativity; to ensure part comparability in a dynamic environment. Sustaining this modeling technique requires strong discipline when it comes to model and drawing management.

I am working on a model right not and I quickly went away from this concept since I need the assembly to use mechanisms. I might connect a few Relations to the sub-models, but I can re-create the core of the geometric relations in the subsequent sketches. I have two dimensions that can scale and tweak the full model at a later time. These two can be driven from the assembly and utilized in a half dozen parts. Now I simply have to make sure that these dimensions will remain variable in the sub-parts by testing the individual sketches to make sure they are stable.

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Re: Sketches and references based on assembled parts: Good or Bad idea?

This is not good practice. Top down design, as Antonius refers to, is using a skeleton or master model to capture 'top level' design information and pass it down the tree to the parts that need it. What you are doing is not top down design, it might be called sideways design, you are passing geometry sideways from part to part. Yes, it's easy to accomplish what you want and to relate parts to each other, but unless you are extraordinarily diligent, you will create a mess of inter-related components and circular references.

In the simple case above, part B relies on Part A and their relationship within the assembly to be correctly created. I better method would be to place the common geometry in a skeleton placed in the assembly and pass the relevant geometry from the skeleton to both A and B within the assembly. Then, both rely on the assy and the skeleton, but neither rely on each other for proper creation.

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Doug Schaefer | Experienced Mechanical Design Engineer
LinkedIn
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Re: Sketches and references based on assembled parts: Good or Bad idea?

BAD idea, for the reasons listed. I had to fix a co-worker's model and it was a nightmare, as everything was all interrelated.

Best to use an inheritance model (master), or a skeleton, or put curves and/surfaces etc directly in the assembly. I'm leaning back towards putting everything back in the assembly, because I've had serious layer issues with both inheritance models and skeleton models where you can't turn off or on the layers in either. If you put all the geometry in the assembly itself, it drives the sub-models like anything else, and your layers work. I've heard the downside is that regen times are increased slightly, but I'll take that tradeoff. The only reason not to do that is if your skeleton or master model is used in multiple assemblies. Also, you can have more than one skeleton and/or master model in an assembly, or in the master model case, in other .prt models. the only thing is that you can only go about 4 levels deep with master models unless they've changed things.

Best of luck.

Re: Sketches and references based on assembled parts: Good or Bad idea?

Thank you all for you valuable advise.

I felt sth wrong so long as I used to come up with troubleshooting every time I need to regenerate a part.

However, I am not familiar with the skeleton / master model technique.

Any tips where to get basics for it and a good example!?

I can see this, http://communities.ptc.com/message/11845#11845 , but is not enough I think! any available of step-by-step example!?

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Re: Sketches and references based on assembled parts: Good or Bad idea?

This is an older tutorial (maintenance required), but it's a good basic overview of skeleton driven top down design.

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Doug Schaefer | Experienced Mechanical Design Engineer
LinkedIn
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Re: Sketches and references based on assembled parts: Good or Bad idea?

Has Skeleton models always been an extention module? In Creo, you don't get to make skeletons anymore.

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Re: Sketches and references based on assembled parts: Good or Bad idea?

You need to have AAX - Advanced Assembly Extension. I think that's always been the case.

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Doug Schaefer | Experienced Mechanical Design Engineer
LinkedIn
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Re: Sketches and references based on assembled parts: Good or Bad idea?

Maybe we need a good tutorial on how to do this -without- having to spend the extra $.

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