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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?

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.

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 Hokanson
Starting Line Products

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william · Guest

Use "Loft" instead of "Sweep"

w

Guest · Posted: Tue Nov 08, 2005 1:10 am Post subject: Re: Sweep Advice

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.

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 Hokanson
Starting Line Products

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