Helical curve swept on a helical curve

Discussion in 'Pro/Engineer & Creo Elements/Pro' started by Bumlinger, Oct 27, 2009.

  1. Bumlinger

    Bumlinger Guest

    I need to create a helical curve that is normal to an existing helical
    curve. A spiral on a spiral so to speak. I have found several curve
    equations that are close, but what usually happens is that the
    secondary curve is not swept normal to the primary curve. The primary
    curve is created by cylindrical equation like this:
    r = 0.75
    theta = 360 * t * 4.5
    z = 0 - 19.05 * t

    It is the equation that sweeps the secondary curve that eludes me.
    Surely, someone must have done this before. Any ideas?
    Bumlinger, Oct 27, 2009
  2. I don't really follow your description yet.

    Does this shape look like a coil formed into a helical curve? Like if
    you formed a phone cord into a spring?

    David Geesaman, Oct 28, 2009
  3. Bumlinger

    Bumlinger Guest

    Yes, exactly that. A phone cord formed into a spring is an accurate
    Bumlinger, Oct 28, 2009
  4. Bumlinger

    Peter Guest

    I have dug out an equation that I believe is what you may be looking
    It produces what looks like a helical phone cord wound around a
    Using a cylindrical CSYS, the equation is:
    primary_turns = 8
    primary_rad = 8
    secondary_turns = 2
    secondary_height = 60
    theta = t * 360 * secondary_turns
    r = 40 + primary_rad * cos (theta * primary_turns)
    z = primary_rad * sin (theta * primary_turns) + (t *
    There are definitely much more elegant ways to write this equation but
    as my old brain is slowing down, I find that I need all the help (and
    prompts) that I can get.
    An elliptical variable sweep (about 3.5 X 1.75) gives a better visual
    result than a circle when trying to follow this curve.
    Hope that it is what you wanted and that I am not too late posting
    Peter, Oct 30, 2009
  5. Bumlinger

    Bumlinger Guest


    Thanks for the formula, it is close but not quite right. I need the
    orientation of the spiral to be normal to the helical sweep
    trajectory. The spiral your formula produces is oriented such that
    the spiral is parallel to the "sketch" plane (if there was one) as it
    rotates about the main axis through the coordinate system. Think of a
    plane through the axis that rotates with the sweep as the curve moves
    down the z direction. I have a graphic, but do not know know how to
    show it in this forum.
    Bumlinger, Nov 2, 2009
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