Ask the Reader: How Do You Model? Plus A Top-Down Modeling Challenge

by Josh on August 12, 2008 · Comments

top-down modeling in SolidWorksI know. You’re just screaming, “I work with the CAMERA. Striking a pose this way and that.” *whoosh, whoosh*

I’m actually talking about how you model your 3D design in . Ah, now this post is suddenly boring. No to get that gritty engineer look on film, just stuff about drawing lines and extruding stuff.

But look here, a question for ya and a challenge for your top-down design idea to be featured on SolidSmack.

How Do You Model Parts in ?
View Results


What’s the difference between Bottom-Up and Top-Down modeling?
Like you see in the poll, Bottom-up design is creating parts, adding them to an assembly and mating them together. To make changes, it’s typical to open the part, make updates and see how the assembly is affected. This can get very time-consuming if you’re going back and forth making those changes. Top-down, on the other hand, is adding a blank part to an assembly, editing it in the assembly to add relationships to other parts in the assembly. For example, you could make one edge line up with an edge on another part, so if one changes, the other will as well.

There’s definitely a place for bottom-up design. However, top-down design allows you to:

  • Create parts in relations to other parts
  • Adjust geometry to suit fit/function
  • Reduce errors within complicated assemblies

Those are just a few major benefits, but once parts are created in the context of how they are going to be used, fine-tuning the parts becomes much easier and, can very quickly, change the production efficiency of your company.

Ready for Top-down assemblies?
So, are you interested in getting started with Top-down assemblies? Thinking about how to start? We’ll get to that, along with the do’s and don’ts of top-down design, in an upcoming post, but first, what would you like to see modeled top-down? Give me your suggestion. I’ll pick the best example of this top-down modeling frenzy and do a post featuring your idea.

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Tagged as: polls, solidworks, tips

  • I'm looking forward to the post, I wish I could read it now, you've got me all fired up for it!

    Toasters are always fun design exercises. (No really, I'm being serious) A few nice parting lines in the shell, plenty of sliding/lever relationships for parts, and all driven by the dimensions of a slice of bread!
  • Dang, good one! That is cool to think about. interesting what shapes control design.
  • Dale Dunn
    In order to showcase the strengths of top-down parametric design, there should be configurations for different sizes and quantities of toast.
  • lukeseed
    Top down may make things faster when designing but becomes a nightmare once in production.
  • I'm thinking of some great big funky wine-rack. Don't ask me where that came from.
  • Ivan
    hmmm... you could do something mechanical with assembly motion, moving parts... engine, scissor lift, adjustable conveyors
  • I made a bbq in my middle technical school and I still use it, it is rusty like hell. But it is pure craftmanship the bbq works always and the rust wont get true the metal!
    So design a DIY (do it yourself) bbq!
  • Stapler! =) I kid, I kid.

    I always finish up with bottom-up assemblies, but sometimes I'll start with top-down designs. If I need a bunch of parts and subassemblies to fit into a small space, top-down is the way to go. But once that design is perfected, I convert it to bottom-up. When dealing with configuration management and ECR/ECNs, the last thing you want is one part to auto-update another.
  • JeffMirisola
    Do you remember "Weird Science"...?
  • haha I prefere bottoms-up when you go there :)
  • Charles Culp
    I model with a mouse in my right hand and my left on the keyboard shortcuts.
  • Hi Josh,

    How about an assembly that shows the dangers of leaving in context relations, ie circular relations, broken relations, too many relations, etc.?

    Daniel
  • Hi Josh-

    Bottom Up is my preference. Why? Because In Context External References don't belong in our universe. Ever Checked In a Part file with these References into an electronic vault? A worm hole opens up and you're transported to the 4th dimension.

    Devon
  • John
    My first choice would be something with Weldments since that's about 90% of what I do. Thanks for all of your informative posts - I really love this site!
  • jeff b
    i began my life as a confident slightly self-centered Top-Downer, but i have sense been converted to a Bottom-Upper. Current job uses a vault and parts get handed around more then baby in need of a diaper change. now maybe 10% of the time when i'm doing a presentation and the parts are all mine, i'll do a combination.
  • Chris Booth
    I agree with Ivan, who suggests "something mechanical with assembly motion, moving parts... engine, scissor lift, adjustable conveyors". For me, top-down design comes into its own when you really NEED to use it, when you couldn't even imagine the shape a part should be unless you see the rest of the assembly going through its planned motion.

    For example: If you go to the Wolfram Demonstrations Project ( http://demonstrations.wolfram.com/ ) and search for "Hoberman" you'll find some examples of mechanisms where the design of one part is very much dependent on the design of other parts, and also the overall results of motion for the mechanism as a whole are difficult to forsee without constantly simulating the motion during the design process.

    Here's the sort of thing you could do with these mechanisms: Watch the web preview of the "Ring of Hoberman Rings" example. Can't you just see how you're really looking down on a new type of connected parasols for sun terraces suspended overhead that does away with those annoying poles that either get in your way as you walk around or else go right through your table?
  • Brad Moon
    I also agree with Ivan, who suggests, "something mechanical with assembly motion, moving parts... engine, scissor lift, adjustable conveyors". Adjustable conveyors preferred.

    That said, I would like to know more about the pitfalls of TDD that Jeff B refers to.
  • You all have had great suggstions. I'm considering some scenarios to show
    and will definitely go over the 'pitfalls', the do's and don't's of top-down
    and bottom-up. Thanks for letting me know what you're interested in seeing.
  • john
    hi, (sorry for my english)
    with the top down method:
    if a part references another one then the part is fixed and i cant mate it.
    im a new user.is there a way to avoid this ?
    thnx
  • John, hi. yes, this is one thing you need to watch with top-down design. I recommend that all parts that reference other parts be fixed. If it's not, then if the unfixed part moves, th references will stay and change the shape (intent) of the part.

    However, keeping parts unfixed can be used while conceptualizing to test out different ideas.
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