Intersection Curve with Sold Body not Closed???

I have single body part that is not overly complex, it is stiched from two lofts
and two planar surfaces.

Create a plane that intersects the body, a 2D sketch on that plane, "Intersection
Curve" and select the body. This should give me the intersection curve between the
solid body and the plane, which by definition should be a closed curve....

Only the curve has small gaps, making it useless for further work!

Are there any tricks to remedy this problem???

(In SWX 2006SP4.1)

/C

 

Instead of selecting the body, you could select individual faces and
see if that helps at all. Also, just to be sure, run all the usual
checks to make sure things are right, meaning Verification on Rebuild,
and Tools, Check. Also, by selecting the "body" I'm assuming you mean
selecting it from the solid body folder or with the bodies selection
filter.

And the other obvious option is that it's just a bug.

Good luck,

Matt

 

Interestingly, Check reports a maximum edge gap of 0.02 mm, which sounds fairly
large to me for a gap in a solid! Selecting individual faces does not change anything.

Too bad, I guess it's a bug in the Intersection Curve code. It propably does the
intersection face by face, and when two faces have a tolerance small enough to be
considered closed when building the solid, it doesn't recognize this and create a
common point endpoint as it should, but rather creates two separate endpoints.

It's rathera annoying that the edges where the gaps appear are originally created
by a Planar Surface, and just picking the existing edges as boundaries. So there
is really no reason why there should be a gap in this edge... And Surface Knit
accepts them as coincident without problems.

Maybe Surface Knit/Form Solid and Intersection Curves have different numerical
tolerances?

/C

skrev:

 

This is my suspicion. This, and similar inaccuracies, can cause havoc.

You might want to try making your two lofted and/or your two planar surfaces
larger than needed, then trimming them to size. No guarantees, but it might
help.


Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"

 

Thanks Jerry, that was actually very helpful.
I made my loft a little higher, and cut off the top with a cut extrude,
instead of letting it finish on the sketch plane.
Intersection Curves are now closed, horray!
/C

 

Actually, I have to say: Gosh!

Since I made the change mentioned above, my assembly rebuild times have dropped to
about 20% of what they were before... (From about half a minute to 5 seconds or
so!) Quite amazing, given it's exactly the same geometry!

 

Cool! This may be another reason why Ed Eaton suggests that you try to make
lofts longer than needed and then trim them back to size. Lofts seem to be
fussiest at the boundaries. By moving the edges of the real part away from
the boundaries of the underlying loft, perhaps SW has an easier time
calculating the intersections.

Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"

 

There are, unfortunately (grrrr...) different tolerances for different
curve types. The most forgiving seems to be composite curve. When
necessary (and only when neccessary, because split line has HUGE
parent/child issues when editing a model) you can create a split line
across your model instead of creating a plane, and use composite curve
of the resulting edges to get your curve (and even convert that into a
sketch if need be and it will be continous while converting just those
edges into the sketch will likely not).

Fortunately, Jerry's workaround worked for you. Any reason not to
resort to the uglier work-arounds is most welcome. Just thought I
would add another option to your bag o' tricks for later on

Ed