why does boundary blend act like this?

[2ms1]

There is something about boundary blends that I have
never understood and now have decided I want to
understand...

Let's say we have two sketches like those shown below.
I've deliberately made each loop up of an equal number of
segments.

View attachment 4796


Why is it that if you try to create a boundary blend
between the two, instead of forming the most direct/short
surface to connect the two sketches, instead it want to
create the twisted up shape shown below?

View attachment 4797

When I try to add a curve in the other direction, the
boundary blend simply will not go at all.

View attachment 4798

However, if I do a swept blend, everything works
perfectly.

View attachment 4799

How do I set up the boundary blend to produce what I
would intuitively consider to be the more logical results
of picture 4 instead of its default behavior of creating
the convoluted mess of picture 2? In this case, I was
able to use a swept blend to achieve what I wanted. But
other times I have had this same kind of result with the
boundary blend when a swept blend would have been
impossible (for example when the two curves have
different numbers of segments).

 

[Jacoolo]

interesting topic 2ms1

for sure You ca not mix 3 curves together when whole boundary does not create closed loop.

in your pictures there are two closed curves in first dir, connected by one in second, at the bottom this boundary is open and Pro/E won

 

[fire-chipmunk]

2ms1

First by the looks of it you have created two separate
closed sections created by using splines.

I would guess by the behaviour of the boundary blend
pictured that the start points of each section are not
roughly aligned. By the looks of it the right sections
start point is in the top right and the left sections
start point is in the top left.

This mean when the boundary blend starts constructing it
will start by drawing a line between the two start point.
Which has caused the line to cross over between sections.

Try redrawing your second second section with the start
point in a similar position as your first section.

For example if the start point is at roughly 2 o'clock on
your first section make sure the start point on your
second section is at roughly 2 o'clock

Hope that makes sense

Simon


Edited by: fire-chipmunk

 

[dgs]

It has to do with what Pro/E considers the start point of each sketch. Pro/E will try to join those start points. I think you can change the start point within the sketch under the 'Sketch' drop down menu.

In your second image, try dragging the white dot on curve #2 to move the origin for the curve in this boundary blend.

Also, you can change the Control Points and pair up the segments manually. If each curve has an equal number of segments, try the piece to piece option.

 

[jsantangelo]

You have two options. Add another curve for the second direction or utilize the Control Points in the Boundary Blend as dgs mentioned. Having equal number of sketch segments makes the Control Points work better too.




Edited by: jsantangelo

 

[gristle]

As the others have said, use control points. If the points in the curve do not align as you would like, you can always add a point on curve before the BB feature and reference that. This helps if you have curves that have different amount/length of segments.

 

[2ms1]

Ok got it. Looks like I'd given up too easily when messing
around with the control points tab. I'd tried going to the
control points tab but I guess the interface didn't click
for me until I spent a little more time messing around with
it after seeing your responses.

 

[dgs]

I've used that interface regularly for years and it still trips me up. If you don't click in the right place in the window and then use the right sequence, nothing happens. Then you get it to work and you don't know what did it. To many things like this in Pro/E.

 

[design-engine]

use control points... sorry so short. fractured right hand

 

[dr_gallup]

use control points... sorry so short. fractured right hand

Dirt biking again Bart?

 

[MGortner]

This is a great question since control points are so
ficky. They easily fail when you tweak parent curves or
even worse, the BB doesn't fail and you're not alerted
that your control points are no longer valid.

I like Doug's suggestion about the start point on the
sketch but I don't see the option when creating a regular
ol' sketch.

Alternatively, you can select start points in the BB
curves/details/options tab. This helps align the points
but it doesn't help ProE connect the dots of each line
segment.

I agree that PROE should make the assumption to connect
line segment ends closest to each other. I'm sure there
is some "intended" functionality for this mismatching but
I can't think of it.

View attachment 4811
View attachment 4812
Edited by: MGortner

 

[dgs]

I meant drag the start point on screen during the boundary blend creation.

The 'Start Point' option in sketcher is under Sketch -> Feature Tools -> Start Point. However, I wasn't able to get the Feature Tools pick to show up with out selecting a vertex and even then the Start Point pick was grayed out. Not sure why.

 

[kdem]

Based on what I've seen in the past the default connection is by ratio. And for the start point I think you need to be in a feature where you specify sections that use start point definitions (such as Blend).

 

[csusie]

The default boundary blend is natural (which aligns
percentages along the boundary, ie 10% matches with 10%...)
if the boundaries have the same number of entities piece to
piece becomes an available option. So like the example you
show above this would be available and it would align all
of the vertices of the boundaries. If you do not have this
condition you can utilize control points to control the
blending.

 

[MGortner]

Great advice. Thanks.I've been using BB for years and
I've never even seen the piece-to-piece option. This
reinforces how important it is to explore every option in
PROE and examine every right-click menu, etc.