trying to make something with vss

[2ms1]

Currently, I have the part shown below in the first 3
pictures. It just uses one trajectory and trajpar to get
the width of the section that is being swept to grow
linearly from small at one end to larger at the other.

However, I would actually like to be able to get better
control of the shape and in fact would like to make more
of an hour-glass-y shape to it where it's small on one
end, gets little smaller in middle, and then flairs out
toward the other end, but also has tangency at each of
the ends (i.e. is no longer growing or shrinking at the
very ends but rather has smoothed out to be parallel with
the trajectory.

Is a VSS the best way of accomplishing this?

I tried to do a VSS with the main trajectory and then an
x trajectory, but the result was unsatisfactory (last
picture). Instead of the cross section changing in size,
it just sorta twisted around.

Anyone have any pointers?

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[mgnt8]

There is a way. I don't have time to do it for you, but I can stear you in the right direction. You need to apply a trajpar variable to sd7. You want to use the cos or sin function in it to control the tangencies.


Do a search for the egg crate model. There was a good example of it in that section.


View attachment 4588
Edited by: mgnt8

 

[2ms1]

Wait, I'm not sure I made it clear what I'm trying to
get. I'm looking to keep the trajectory highlighted in
Fig.2 (of the initial post) the same and also the
"thickness" of the thing
(basically sd7) consistent throughout the part.

The only thing I would like to have different is to have,
instead of the top view of the part looking like an
isosceles trapezoid, an outer edge shape dictated by a
curvy spline that might look like one of the two Figs
below.


In other words, the part is fine as it is, except that I
need to be able to add control of the width by an
additional trajectory (x-trajectory?). I would like to
drop using trajpar so I can use a free-form spline. I
don't think it's possible to synthesize the very organic
shape I need by using trig functions in trajpar. When
I try to just simply draw a spline on the Top plane (i.e.
normal to the spline serving as the main trajectory) and
use it as an x-trajectory in the VSS, I unfortunately get
what you see in the last figure of the initial post
above.

Sorry if I am misunderstanding you completely. But I
think I may have conveyed what I'm going for poorly in
the first post? I hope that's all it is and that there
is just some simple procedural aspect I'm getting wrong
with VSSes.

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(Note: these images are of just flat extrusions for
mockup purposes showing what top view would look like)
Edited by: 2ms1

 

[tobbo]

Use a Graph!


the graph will then controll the dim so you get the result you want.


//Tobias



Edited by: tobbo

 

[mgnt8]

Sorry I misunderstood. Graph would work. Although I don't see why adding secondary trajectories won't work either. Did you try them without the trapar relations?

 

[kdem]

You also might try splitting up the features. I had trouble when trying to add the angled flange. I ended up creating surface features for half the geometry, merged and mirroredthe surfaces, and thickened the surfaces. Here is what I ended up with:


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Edited by: kdem

 

[2ms1]

Guys, I am not familiar with the Graph tool but if it's
the easiest/best way of doing this then please tell me
more about how I would use it. I wish a simple side
trajectory like in the attempt shown in Fig.5 of post #1
would work but no matter what I try I always seem to get
the tilting cross section effect as visible in Fig.5.
Why would what I am doing there not work?

kdem, it's nice to see that you were able to accomplish
what I'm going for. Did you try making a vss the way I
did in the last picture of post #1 ("Fig.5") and have it
fail in the same way? Could you describe a little more
specifically what you did in terms of breaking the part
down into pieces and then merging them? I'm not quite
sure what you did but it's starting to look like it might
be the way to go.

 

[kdem]

I worked with it a little more and was able to get it to work with two sketches and a single VSS which is different than how I did it earlier. The problem I found was in the dimensioning of the section and the VSS option chosen. For the VSS option try Normal to Projection in the Section plane control and the correct direction reference based on how you set up your curves (mine was the TOP plane, the origin curve was on the SIDE plane and the spline was on the TOP plane).


View attachment 4595


As I worked though this I found that dimensioning the flange from the center caused problems.Assuming you want the flange to remain the same as it follows the shape of the spline try dimensioning your section so sd3 and sd4 in the fourth picture of your first post are dimensioned from the spline curve.


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If you're still unable to get it to work I can put together a student version file, since that appears to be what you're using.