622 suffers do-overs in CAD too

If you’ve been reading my blog for any time at all, you know that I throw out about half the things I make.  The first version is never good enough, but it does teach me how to make one that is.

So, it should come as no surprise that I just deleted almost the whole CAD model that I’ve been working on all week.  I learned a lot about OnShape through that first version, and just as I would be able to see the crooked parts and glue blobs on a physical model, I could see that this virtual model could be improved too.

Here are some things I learned this week:

  • Use variables.  I defined a variable, #etch, which is the planned thickness of the etched parts.  You can use this variable in expressions anywhere you can use a number.  So, for example, if you want to create a part that is made of two layers of metal, you might extrude it to “2 * #etch” depth.
    Hilariously, it took me several evenings of switching back and forth between LibreOffice Calc (my spreadsheet tool) and OnShape before I realized I could define a variable for the scale too.  Now, rather than hard-coding the boiler diameter at 0.68″, I use the scale and the actual dimension – “(58 + 2*5/8)/#scale” – it comes out the same, but I can see the actual boiler diameter and plate thickness instead of a random number.   Theoretically, I could get a head start on changing the scale by simply changing the one variable.
  • Create most of your parts in a single Part Studio.  The user interface guides you in this direction by presenting the studios as tabs; so you know when you get to a hundred parts, you’re going to struggle with the user interface.  However, the beginner tutorials don’t give much of a clue as to how to organize your work.
  • Within the Part Studio, create the parts in relation to each other.  This was the main thing that made me throw the original frame in the bin.   From the beginner tutorials, I got the impression that you need to create the parts separately, and assemble them in the Assembly Studio, but that means that you can’t use lines from one part to create another.  If you create the parts as one large sub-assembly in the Part Studio, then they magically fit together even if you change one of them!



2 thoughts on “622 suffers do-overs in CAD too

  1. To paraphrase a wise modeler “Most CAD models take two or more attempts before they turn out. The first time, you figure out how to do it, and the second time, you do it right.”

    Someone should let people know this 🙂

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