Interesting "Bug" In Sweep Curves (Wildfire 4)

Discussion in 'Pro/Engineer & Creo Elements/Pro' started by Lehnsherr, Oct 28, 2010.

  1. Lehnsherr

    Lehnsherr Guest

    Yesterday and today I set out to draft a cooling coil for a coworker.
    It's a simple, flattened spiral of copper tubing lying on its side,
    with two "risers" coming up from it (to come up and over the side of
    the tank the coil will be sitting in).
    Think oblate spring lying on its side, with its two ends pulled out
    and running vertically upward, then bending over the lip of a tank.
    The first riser descends to the bottom of the first coil, and then the
    tube turns in 6 coils. The ends of the coils are basically 180-degree,
    2-inch-radius bends of the tubing.
    At the end of the last coil, the riser comes up off the top of the
    coil, rises up the side of the tank, and over (shaped like a candy

    I started out with a single set of Datum Points, using Offset
    Coordinate System Datum Point and Cartesian coordinates, defined in
    the order they would occur along the tube. The end of each coil would
    consist of two 90-degree bends, and thus had two of these Datum
    Each coil-end was progressively defined to be ~1 inch further in Y
    than the previous end (those two points' Y-coordinate was 1" larger
    than the previous two points) to get the spiral effect.
    I then used this set of Datum Points to define a single Datum Curve,
    using "Single Rad" and "Whole Array", starting from Point 0.
    Then, I created a Swept Protrusion along this Datum Curve, using
    "Insert", "Sweep", "Protrusion", "Select Traj" (here selected the
    first segment of my Datum Curve), "Curve Chain", and "Select All".

    Originally I drew my sketch (for the sweep) of the cross-section of
    tubing so that it would start out on the inside of the curves of the
    riser... however, this would put it on the outside of the curves of
    the loops, making the tube itself have different bend radii depending
    on if it was in a loop or in the risers, because the driving Datum
    Curve was using only one radius, Single Rad.

    So instead, I changed my sketch so that the sketch would sit 90 deg at
    the side of the Datum Curve (90 degrees to the plane of all the
    "bends"), and the plan was it would stay at the side of the curve all
    the way through all the loops, thus keeping the same tubing radius
    throughout the part. Here's where the bug appeared-- in practice, as
    ProE drove the sketch along the length of the Datum Curve, after a
    loop or two the profile started to "migrate around" the Datum Curve
    until at the end, it had moved to the top/outside of the Datum Curve
    instead of sticking to its side!

    Of course, this resulted in the tubing's "bend radius" gradually
    changing throughout the part, rather than staying the same as I wanted
    it to.

    If I make the Datum Curve use multiple radii instead of Single Rad,
    and put the sketch back on the inside or outside of the turns, this
    "sort of" fixes the problem-- but Pro/E still restricts my choice of
    radius to the max for the *smallest* turns... so the bigger turns look
    more like rounded corners than actual 180-deg bends of tubing.

    Any suggestions?
    Lehnsherr, Oct 28, 2010
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