Sweep Advice

Discussion in 'SolidWorks' started by J Parr, Nov 7, 2005.

  1. J Parr

    J Parr Guest

    Is there anyway to transform a circle (start) into an ellipse (end) along a
    sweep path?

    Think of an exhaust shape.

    Do I use the sweep command or another?
     
    J Parr, Nov 7, 2005
    #1
  2. J Parr

    Brian Guest

    You will want to use the loft command. One end the ellipse, with two of
    the ellipse points constrained coincident to the plane on which the
    centerline lies. On the other end, create your circle and use the split
    entities command to break the circle into 4 cordial arcs. Constrain two of
    those points to your centerline plane and the other two at 90 degree
    intervals to the centerpoint of the arc ( several ways to do this ).

    It is not 100% necessary to break the circle into segments, but SW may
    decide to connect your ellipse to the circle in an inappropriate fashion,
    giving it an hourglass shape. SW also does this if lofting between two
    circles along a centerline. The only way to be sure is to provide points
    which sw will align to. It usually is easiest to pre-select the two points
    of the sketches that you wish aligned ( although inexplicably, sometimes sw
    won't allow it for some sketches, but does for others ) before clicking the
    loft command.
     
    Brian, Nov 7, 2005
    #2
  3. J Parr

    william Guest

    Use "Loft" instead of "Sweep"

    w
     
    william, Nov 7, 2005
    #3
  4. J Parr

    That70sTick Guest

    Easy. Done it plenty. Sweep works perfectly for this.

    Start with this:
    --Use a straight line for a path.
    --Make two guide curves that define ellipse major and minor axes along
    the entire length of the sweep path.
    --Make section with a single full ellipse, center of ellipse
    constrained with pierce to the straight line path, axis nodes
    constrained with pierce to the other two guide curves.
    --Make your sweep with ellipse sketch section, straight line sketch for
    main path, and two guide curves

    Once you are familiar with doing this from a straight path,
    transforming the technique to curved paths is logical.

    Remember a circle is an ellipse with equal major/minor axis lengths.
     
    That70sTick, Nov 7, 2005
    #4
  5. J Parr

    ed1701 Guest

    That 70's tick has good advice - if you can do it, a sweep with guides
    gives great results (a sweep-with-guides is a macro for creating a
    loft) The only trouble is that you may have to be extra careful
    creating the guides. Remember, you need only two - one for the major
    axis width and one for the minor assuming that the path isthrough the
    centerpoints. Lots of folks run into problems over-constraining the
    sections - only use as many guides as required to fully define the
    section.

    If the loft is the only way to go, Brian is correct that it can be
    dodgy with the points to connect closed contours like circles and
    ellipses. Even if you think you are very precise when you make your
    selection it can still be a little off which might mess up some
    designs. Splitting curves is a solid way to help control but can mess
    things up in some situations. You can add a guide curve to control that
    connection point precisely without having to split the curves. Then
    you can actually delete the guide from the loft defnition (after the
    loft built once) and the loft will still use that connection vector!
    This is a tricky way to get the pick points precise without having the
    guide actually influence the shape (again, depends on your design
    goals, but my guess from the info in your post is that you don't want
    the guide to mess with the geoemtry)

    One last thought - you can also choose to do a 'centerline' loft if you
    need the transition to follow a 'path'.

    Whih of the three routes you take depends on the geometry and whatever
    future editing you expect to do. Hard to pick one without seeing the
    application, but it would probably be a good educational experience to
    do it all three ways (when time permits) to see the differences in
    setup and results.
     
    ed1701, Nov 8, 2005
    #5
  6. J Parr

    Brian Guest

    If you need to ensure that you are closely following your centerline and
    connecting points properly, construct an additional loft with a straight,
    perpindicular ( to the cross section shapes ) centerline of the same length
    as your curved one. Compare volume of the two solids. If the solid using
    the curved centerline is smaller, its a good indication that its loft points
    have not been connected properly.
     
    Brian, Nov 8, 2005
    #6
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