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Thread: Post SOLIDWORKS Designs Here

  1. #51
    cwilliamrose's Avatar
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    Hi Mark,

    Looks good in the screen shot. I tried to download it from GrabCAD but there's only the assembly file there, the part files aren't on GrabCAD so when you open the assembly the part files are not found which causes an error. In order to get all the parts and pieces it's best to use the 'Pack and Go' tool to create a ZIP file. You can then upload the ZIP file to the website.

  2. #52
    Mark Meredith's Avatar
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    Bill,
    Got it, thanks. Reloaded with the zip and a couple of images.

  3. #53
    cwilliamrose's Avatar
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    The link to the new upload is https://grabcad.com/library/scott-32...assembly-zip-1.

    I took a quick look last night and the first thing I noticed was that most (all?) sketches are under defined. In my experience if you don't fully define your sketches interesting things can happen and none of them are good things. I try to always fully define my sketches at least in terms of the geometry in the sketch that actually creates the solid. It's best to fully define them all since it's easier to see if you missed something when one of the sketches is not fully defined (and has the "-" sign as a prefix). Things like splines are a PITA to fully define sometimes and I will resort to "fixed" constraints when all else fails. I do not recommend using "fixed" constraints for anything other than a temporary tool which gets removed later when better constraints are applied.

    I'll look at the assembly in more detail later but I'd say as an early learning exercise you did a great job on a difficult to model object.

  4. #54
    SOLIDWORKS Support Volunteer Jeffrey Meyer's Avatar
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    Pearls of wisdom

    I would even go one step further and say that in addition to fully constrained sketches it's best to assign a material with known density to the part(s) so that further down the line you can extract the weight of the assembly. (In aviation weight is the name of the game). At the very beginning of creating the geometry I would even give some thought to the orientation in space and placement of the origin of each part. You can also make part templates with pre-assigned materials and other custom properties that you commonly use.

    All nuances, but nice work Mark

  5. #55
    Mark Meredith's Avatar
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    Quote Originally Posted by cwilliamrose View Post
    ...most (all?) sketches are under defined.
    Bill, how do you do that? I recently went through some text material on repairing errors and external references (SDC’s Solidworks 2016 Advanced Techniques). Wish I had known these tools earlier because I’ve had lots of broken references as I’ve had to modify parts. (It got easier when I started using assemblies in the main gear/tailwheel so only had to repair mates). Anyway, much of this text treatment was about OVER defined drawings or bad external references, not UNDER defined. I picked a random drawing (sketch 4 of the Fork, part of the Tailwheel Assembly) that showed the (-) symbol. Much of the drawing lacked dimensions, so I added them. But the (-) remained. What am I missing?

  6. #56
    Mark Meredith's Avatar
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    Quote Originally Posted by Jeffrey Meyer View Post
    ...At the very beginning of creating the geometry I would even give some thought to the orientation in space and placement of the origin of each part.
    Jeff, thanks for the pearls (what’s that line about pearls before swine? ) I’m unclear about what I need to do differently regarding orientation and origins. For a circular part (lots of them in the tailwheel) I just placed the origin at the center of the circle, but placed it fairly randomly for more complex shaped parts. Can you give some more insight into orientation/origin considerations as I start a new drawing? Thanks!

  7. #57
    Mark Meredith's Avatar
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    Advanced Text Books

    Does anyone have recommendations regarding textbooks? I've been through a couple of them from SDC on basic and advanced techniques, subscribe to Lynda for online SWx training materials, and have watched a bunch of Youtube videos. I much prefer the more organized training materials over the haphazard (but free) Youtube stuff. I found nothing in a Google search for additional advanced books (including texts on the soup to nuts design process using SWx). I did download one on Finite Element Modeling that has some material about the design process including stress analysis. I just started reading it; it looks worthwhile but your comments above tell me I'm missing some key modeling skills.

    By the way, here's my main gear. It was much easier than the tailwheel but not as complete (nothing internal to the strut, no brakes, etc). But it moves which is cool. Clearly it also suffers from under-defined drawings. Name:  IMG_20170103_103135227.jpg
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Size:  86.0 KB.

  8. #58
    cwilliamrose's Avatar
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    The biggest issue with Sketch4 is the splines which are a PITA to fully define. I'd use tangent arcs instead if that were possible for this part and it would also make it easier to machine.

    Name:  Sketch4-Temp.JPG
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    First, I changed to ANSI dimensions because ISO drives me crazy.

    I added a colinear constraint to the vertical lines at the end of the fork and symmetrical constraints to some other points and lines. Then I added some dimensions to the lines and points to make them turn black. Finally I dimensioned the splines. This requires angle and distance dimensions at each spline point. Or you can fix them but I didn't do that here. The 179.95° angle on the outside spline could have easily been a tangent constraint instead.

    For a part like this you can model half of it and then mirror the other half using the Mirror Feature tool which makes the parent sketch a little easier to deal with. Or you can mirror the sketch entities but that's not usually ideal due to the clutter you add to the sketch.

  9. #59
    Mark Meredith's Avatar
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    Thanks for taking the time to do that, Bill! Very helpful. In the Youtube videos I've watched the instructors always dimension the arcs but I didn't know why. I've used the mirror more and more (and dynamic mirror which is nice), but usually mirroring the sketch not the solid model. I'll work on that. I'll pay attention to turning lines black also. What kind of bad stuff can result from an under-defined drawing?

  10. #60
    cwilliamrose's Avatar
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    Anything in a sketch that is not fully defined can move. I have never understood all the mechanisms that allow this to happen within a part or assembly but I have been the victim of it more than a few times which is why black is one of my favorite colors. These days I pretty much only see it when I'm working on another person's models where I'll edit something and a seemingly unrelated feature goes crazy because the sketch that feature was based on changed. I try very hard to thoroughly check for fully defined sketches in a model I didn't create before I change it -- and I only work on a copy of the original in case kablamo!! occurs.

    I also like to get rid of any 'InPlace" mates which I consider to be time bombs when you're making changes to an assembly. By 'changes' I mean editing a feature or sketch as opposed to adding a feature to modify another feature when a simple edit should give the same result -- something I consider to be very poor technique. People who do this are often conditioned to do so by past experience where models have blown up (collapsed, turned red, etc) due to being a house of cards full of under defined sketches, lots of external references, etc. If you don't touch the existing features the model will usually remain whole but you end up with a feature tree a mile long that is impossible to deal with. The other group of people who do this are coming from a non-parametic CAD program where this is the only way to edit a model.

    There are many ways to create a model and several of them can be considered 'correct', the rest not so much. My methods are mostly the result of experience and liking my models to behave like real parts.

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