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ptc-47663301-Visitor
1-Visitor
August 19, 2013
Question

How do I create this shape? Ellipsoid?

  • August 19, 2013
  • 6 replies
  • 8277 views

I am trying to create a shape like thishttp://www.google.com/imgres?sa=X&biw=1280&bih=890&tbm=isch&tbnid=gUrw4Oqrfr_kvM:&imgrefurl=http://commons.wikimedia.org/wiki/File:Ellipsoid_Labelled.png&docid=4VgrjD0GQ321rM&imgurl=http://upload.wikimedia.org/wikipedia/commons/a/ab/Ellipsoid_Labelled.png&w=2170&h=1237&ei=FX0SUt3hKoSGyAHQtIBI&zoom=1&ved=1t:3588,r:22,s:0,i:164&iact=rc&page=2&tbnh=169&tbnw=298&start=15&ndsp=27&tx=232&ty=48


Kind of a revolved ellipse but I want the Ry value of the ellipse to be different on the front and right planes. If I construct it from boundary blends I'll get a pinched surface at the poles. Is there a way to achieve this sort of thing with variable section sweeps? I really need a variable revolve feature please 😉


Any suggestions appreciated, thanks!


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6 replies

P
ptc-47663301-VisitorAuthor
1-Visitor
August 19, 2013

I should clarify that the central profile should be an ellipse not a circle. More like this actuallyhttp://img.tfd.com/ggse/e6/gsed_0001_0030_0_img9466.png

J
jameswesterfiel1-Visitor
1-Visitor
August 19, 2013
Like this?

[cid:image001.png@01CE9CE3.2E7F0A70]

[cid:image002.jpg@01CE9CE3.2E7F0A70]

[cid:image003.png@01CE9CE3.2E7F0A70]
P
ptc-47663301-VisitorAuthor
1-Visitor
August 19, 2013
Yes I think so, can you highlight the profiles on the 3 datum planes, they
should all be ellipses. How did you create it?


M
mpeterson1-Visitor
1-Visitor
August 19, 2013
I suggest creating 1 quarter of this and mirror and merge and then another mirror and merge.

Start by creating one of the elliptical halves of either frontto top view. Make sure the end points of the curves are vertical or normal with the adjacent datum plane. If not you will end up getting creases where the halve merge.

Next create the elliptical curve in the other plane. Make sure the end points are like done before (vertical/normal to adjacent DP, but also coincide with the end points of the first curve.

Next create a boundary blend using those tow curvesfor the first direction and no curves in the second direction.
Set the constraints for each curve to be normal.

Next do the mirror merge steps and should be good with no creases.

Good Luck,

Mark A. Peterson
Design Engineer
Varel International

B
bokm96061-Visitor
1-Visitor
August 19, 2013
creating sacrificial side surfaces that are simple extrudes of the
elliptical shapes prior to the the creation of the boundary surface will
allow you to select those surfaces to help constrain the ends of the
boundary blend to be wither tangent OR CURVATURE continuous.

think of these surfaces as construction only that would be layered
off.....i find that the tangent constraint is sometimes more forgiving that
simply "selecting" normal to plane for boundary conditions.

you can also play with the "stetch" value for your boundary conditions as
well.....i think as this value as the " initial velocity" as if you were
throwing a ball at that that constraint definition....the higher the number
the closer the surface will track along this boundary condition (higher
velocity" they lower the number the surface will can "peel away" quicker
(lower velocity)



G
Greg_McMurray1-Visitor
1-Visitor
August 20, 2013

This can also be done with a few construction curves and two variable section sweeps sketched with conics.


Surface quality may be a little better than a trimmed back boundary blend.


Mesh is definitely better than a 3 sided quilt with singularity


The technique was documented and demonstrated here:


http://www.mcadcentral.com/creo-modeling/17699-nose-c-ne-help.html

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