Parabolic Sketch for Torispherical Vessel Head

Discussion in 'SolidWorks' started by western1812, Dec 17, 2005.

  1. western1812

    western1812 Guest

    I am modelling a ASME pressure vessel with a Torispherical(parabolic)

    What is the best method for constraining the spline points?

    western1812, Dec 17, 2005
  2. western1812

    That70sTick Guest

    If you are designing a pressure vessel and need a true parabola, use a
    parabola curve and not a curve. In a 2D sketch, use "Insert --> Sketch
    entities --> Parabola". Using a spline to trace a parabola will
    introduce a measurable amount of error into your CAD geometry. Might
    as well start with perfect CAD geometry, as deviations can be copied
    with amazing precision with CNC.
    That70sTick, Dec 17, 2005
  3. western1812

    matt Guest

    If you are making a parabolic shape, the best way is to use the parabola
    sketch entity, not a spline. A spline will tend to have tangency
    problems at the ends and they're always interpolated geometry anyway, so
    it won't be exact.

    If still you feel the need to use a spline, there are a few ways with
    different merits and detractors that you can use:

    - if you plan to use a spline as a parabola, you will either need to
    overbuild the spline and trim it back or set appropriate end tangency

    - use the auto dimension and just put dims on the spline points relative
    to something off the spline, preferably something stable, preferably the
    part origin.

    - use the Fixed constraint on all spline points

    - make the spline proportional and only lock down the ends

    - don't worry about it and take your chances with it moving around.
    this is actually not as bad as it sounds. splines that are locked to
    other things tend to be less predictable than splines that aren't, even
    though the common wisdom is to shake your head in horror at blue
    matt, Dec 17, 2005
  4. western1812

    TOP Guest

    A torispherical head consists of two arcs, one with a large radius and
    one near the junction with the cylinder having a small radius. The
    closest conic to this shape is an ellipse. You do not need a spline.
    TOP, Dec 18, 2005
  5. western1812

    TOP Guest

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