Creating a sweep, loft or boundary boss along a 3D Spline?

[gcmospeada]

Hey folks,

I'm new here, and not exactly a seasoned SolidWorks user, so if there's anything about this question that breaks protocol or is overly ignorant, I apologize in advance.

I've got identical sketches on two arbitrary planes which are predetermined (fixed inputs to the problem) and I need to create a swept feature between them along a 3D-sketched spline. The end profile sketches comprise a shape within a shape, so the extruded form should be a sort of tube with a shaped hole through it. I've described the problem with generalized example pictures here:

http://imgur.com/a/2S0w1

Any thoughts on how best to accomplish this? I've been struggling with this problem for over 2 days now, and haven't come up with that [probably obvious] "weird trick" that makes it all work.

 

[JMirisola]

Have you tried a centerline versus using a line corner to corner? Even with that, I'm think you'll need more guidelines to make it happy.

Jeff Mirisola, CSWE
My Blog

 

[gcmospeada]

For Boundary and Loft features, the guide spline must be coincident to the profile curves; it can't be in the center.

The problem with using multiple splines is that I can't guarantee their curvature relative to each other. I need a way to simply ensure that the profile of the sketch, which should be sufficient information to fully draw the extrusion, remains normal to the path, whatever that path is. I can tweak and get "sort-of close", but at a great expense of time and in a way that is fragile and won't easily follow future changes in the end parts' locations, if there are any.

On another subject, I was hoping I could at least try to use my corner guide spline as a guide curve in the Sweep feature, but if I select it as a guide curve, the operation inexplicably fails. I've tried this several times in a number of contexts, and can't get it to work. So it's shown unselected in the pictures.

 

[gcmospeada]

Oh, and if by "centerline" you mean changing the spline to construction geometry, this prevents it from being selected as a curve for Direction 2. It apparently has to be a regular spline (solid, not dashed).

 

[JMirisola]

I get all that, I was referring to using one line through the center. I was throwing out a suggestion.
As you've pointed out, getting your splines to play nicely together with regards to their curvature will be problematic. I'm messing around with some ideas, but nothing seems to be working yet.

Jeff Mirisola, CSWE
My Blog

 

[TheTick]

Looks like your ends are the same profile. Use a sweep. A loft is just cheating. You want a constant profile that results from a sweep.

You're almost there with the sweep. You just need to make your second guide curve and relations to it a little better.

Make your second guide curve between corresponding points on your ends. On your section sketch, start with a construction line with pierce constraints to your secondary guide curve and main sweep guide.

THEN draw your section (in the same sketch as your new construction line). Constrain the section sketch such that you use the construction line only for orientation, not for size.

You could actually use a block for your cross-section. Then it will be much easier to control orientation and not have a bunch of constraints fighting one another.

 

[gcmospeada]

TheTick, it sounds like you may be onto the solution, but there are some things I should clarify first.

> Looks like your ends are the same profile.

They are. I created the profile in the first object, and then created a sketch block from that to guarantee the second part has an identical shape.

> You just need to make your second guide curve and relations to it a little better.

I agree, I wish I could do this in a deterministic, non-brittle way, that would correctly respond to adjustments in the relative positions of the end sketch planes. Unfortunately, there is no "offset" tool for 3D splines that would maintain the relationship I think I need.

Constrain the section sketch such that you use the construction line only for orientation, not for size.

This is the part I think has some promise, except I don't know how to do this, or maybe even what it means. How can I tell the software to ignore the size input, and only follow it for rotation? I am assuming that making the splines effectively equidistant along their lengths is impossible or impractical (and again, would be an unacceptably "brittle" solution if attempted by hand); is there a technique I'm not aware of?

Thanks for your input!