×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Strategy for multiple curves at corner
4

Strategy for multiple curves at corner

Strategy for multiple curves at corner

(OP)
Can anyone suggest a strategy for getting good curvature bringing these curves together? Every time I add a hard constraint (such as a guide curve for a loft, or Direction 2 for a boundary), the surfaces become wrinkled.

The whole part is a just a rectilinear box with curved edges and a slightly curved top, and flat bottom, and this model is one corner of it.

The part will be injection molded.

I've put many hours into this, including training (instructor couldn't figure it out), tutorials, books, so I think I have to ask for help now.



RE: Strategy for multiple curves at corner

Start by cutting all the specified radii in half, and then again if necessary, until SW is able to produce a more cubist representation of what you want. Then increase the radii until it gets wonky, and then back them off a bit.

Mike Halloran
Pembroke Pines, FL, USA

RE: Strategy for multiple curves at corner

(OP)
@MH Thanks for thinking about this. That sounds like something very interesting, but I don't think I understand it. If all radii are at 50%, then the whole model is merely scaled, and so the SW internal algorithms won't be affected.

If you mean apply this rule only to particularly troublesome constraining curves, then I have gone much further than that: I've completely omitted them, for example the plan view curve on the split plane. This provides a very comprehensive improvement, but can only be implemented for the first surfaces you make (because later, something else will have to align with those unconstrained edges).

RE: Strategy for multiple curves at corner

Where I'm going is that SW is basically just always trying to solve a set of equations, which you define indirectly, and that it is possible to define a set of equations that have no useful solution. That's where you are. So, yes, sharpen the weird edges, and/or change the way in which they are defined, and you have a chance of understanding exactly how SW is interpreting your desires differently from the way you think you have defined them.

Mike Halloran
Pembroke Pines, FL, USA

RE: Strategy for multiple curves at corner

(OP)
@MH Thanks for the clarification. That did finally dawn on me, and since then have been making many experiments, mostly splitting curves or removing constraints. Both work well, but only for the first set of surfaces, because after that, the first set become constraints for the subsequent surfaces, which then wrinkle. I just tried some radius manipulation; there are affects, but not improvements.

Perhaps somebody's seen this before and can be a more specific, or would like to have a try with the model (not that I want my work done for me, though).

Thanks very much for your thoughts, MH; it's reasssuring to know that I'm generally on the right track.

RE: Strategy for multiple curves at corner

I must be missing something because it looks pretty good when I open it. The only thing I do see is something kind of wonky on what I will call the top surface at the radius 90° corner.

RE: Strategy for multiple curves at corner

(OP)
@djhurayt Thanks for looking at it. Yes, wonky. I betcha a bag of pretzels you can't get rid of it. Turn of curvature to see just how bad it is.

RE: Strategy for multiple curves at corner

OK so that is the problem child area, let me take a deeper look-see

RE: Strategy for multiple curves at corner

On "Surface-Loft1" and "Surface-Loft2": Try changing the Start/End Constraints (both Tangent Lengths) to .1
Or, change the Start Constraints to "None".

You are using SW 2014? I have 2015, so can't send it back to you.

Chris, CSWA
SolidWorks '15
SolidWorks Legion

RE: Strategy for multiple curves at corner

Seems like you're working backwards, building corners first and then main faces. I'm sure there are more efficient ways to fail, but...

RE: Strategy for multiple curves at corner

(OP)
@ctopher Thanks very much, I see your point. However, I've used the tangent lengths to get the unconstrained edge at the split plane to align with the required shape shown in plane 'split' (instead of using it as a guide curve). If I change the tangents, then I will have to use the sketch as a guide, which will then drive wrinkles.

Another purpose of the tangent is to ensure that the flattening at the 45 plane pushes out toward the more rounded front and side planes. This flattening is very easy to achieve with a file and and epoxy cast, but is the source of the problem. I don't know how to get the flattening effect without pushing the tangents.

So I tried it anyway: tangents to 0.1, apply 'corner plan' sketch as a guide, and I get distortion caused by the change from line to pline in 'corner plan' sketch. Adjusting tangents does not yield an improvement.


RE: Strategy for multiple curves at corner

I got rid of that wonky area, but the curvature still shows some inconsistency on that edge

Scott Baugh, CSWP pc2
Gryphon Environmental
www.2gryphon.com

Quote:

"If it's not broke, Don't fix it!"
FAQ731-376: Eng-Tips.com Forum Policies

RE: Strategy for multiple curves at corner

(OP)
@TheTick: I have removed the other surfaces for clarity, leaving only their constraining edges. Yes, I have failed. That's why I'm here.

RE: Strategy for multiple curves at corner

AK, can you confirm your version of SW, it looks like 2011. ???

RE: Strategy for multiple curves at corner

(OP)
@SBaugh Thanks very much for the attempt. The sketch 'corner plan' on plane 'split' is a constraint. The curves must not go outside this line, and this constraint drives some of the trouble at the top flattish area.

Also, there is supposed to be a flattish area at 45 degrees around the corner which seems to be not present in your screenshot, as depicted in sketch 'corner top.' Imagine taking a flat file to the corner (which is what I did) and largely flattening the corner, then blending it with the file into the other two edges, which rounded, not flattened.

RE: Strategy for multiple curves at corner

Sorry. Maybe a bit harsh, but I want to drive home a fundamental flaw in your approach.

My point is that the corners should probably not be built independently. If the main faces and edges are used to drive the corners, it will require less definition and get a smoother result.

RE: Strategy for multiple curves at corner

(OP)
@djhurayt Yes, 2011.

RE: Strategy for multiple curves at corner

(OP)
@TheTick I have found just the opposite: with fewer constraints, it is much easier to get wrinkle-free curved surfaces. Therefore, if you have a particularly difficult area, it may be worth creating it first.

However, this approach can only work for the first one or two surfaces (because subsequent surfaces will have to be constrained by preceding surfaces).

RE: Strategy for multiple curves at corner

RE: Strategy for multiple curves at corner

(OP)
@djhurayt Looks good. How did you do it? I can open 2011 files, sorry, you're probably way ahead of that.

RE: Strategy for multiple curves at corner

well that would make a difference then... didn't realize that was a Constraint. That Wonky area makes it tough to get a clean curvature.

Scott Baugh, CSWP pc2
Gryphon Environmental
www.2gryphon.com

Quote:

"If it's not broke, Don't fix it!"
FAQ731-376: Eng-Tips.com Forum Policies

RE: Strategy for multiple curves at corner

(OP)
@SBaugh Yup, that's the stuff I keep getting. Isn't this a common problem?

A little clarification just in case: the wonky area is a fill, the final portion left over after doing the main portions of the corner. It is not a constraint. The constraints are defined by the sketches 'cross top', 'long top', 'corner top', and 'corner plan.' It is acceptable to not follow 'corner plan' precisely, but the surfaces must not go outside the corner plan.

I have achieved an excellent top (the wonky area) by sweeping 'long top' along 'cross top' but then it becomes a hard constraint (after trimming it) for the main parts of the corner. This was the approach used in the iphone tutorial, but the iphone has only a simple corner (same profile all the way around the corner).

RE: Strategy for multiple curves at corner

2
Yes, unfortunately for you we are on 15. But let me try to walk you through it. The basics are that I did mine with one lofted surface. I used you geometry to generate my curves and obviously had to make some assumptions.

  1. create Plane1, parallel to your Front Plane and through the point highlighted



  2. create Sketch1 on Plane1 using “convert edge” on your Surface-Loft2 profile



  3. create Plane 2, which is actually just a 0.0 distance offset of your Right Plane; only did this for continuity of the process and to keep the new stuff in one area
  4. create Sketch2 on Plane2, done same as Sketch 1 (see step 2)
  5. create Plane3 using the three highlighted points; assumption being that you want your surface to go through these three points only without the “wonk”



  6. create Sketch 3 with two lines from the end upper endpoints of Sketch1 & 2 and a tangent arc that is also coincident with the end of the line that is the intersection between your Surface-Loft1 & 2, this is also one of the same points used to create Plane3



  7. create Plane4, parallel to your Top Plane and through the point highlighted



  8. create Sketch4, using the same idea as Sketch3 (see step 6)



  9. create a Surface-Loft using Sketch1 & 2 as the profile curves, and Sketch3 & 4 as the guide curves



  10. wrap it up and put a bow on it

RE: Strategy for multiple curves at corner

(OP)
@djhurayt Wow, that is a very impressive answer! I was expected a few short bullets. Thanks a million for taking so much time. It's after midnight here, I can't go on, but I will follow this guide closely tomorrow morning and let you know how it goes.

Many thanks to all for participating in my puzzle!

RE: Strategy for multiple curves at corner

(OP)
@djhurayt Thanks again. I've followed the steps, see pic below. You haven't shown your curvature; is it better?

The profile on the 45 degree plane is meant to flatten the corner. To get that effect, tangency controls are needed there. Loft only offers tangency controls on start and end profiles, so I also modified your steps to make two lofts, with a similar outcome.

A stellar effort, though, and much appreciated!

RE: Strategy for multiple curves at corner

(OP)
Here's what I've decided to run with for this shape:
1. Concede that secondary constraints (boundary dir2 and loft guides) sometimes cause wrinkles.

2. In lieu of secondary constraints, use tangency controls.

3. Make two lofts, to get the tangency controls at the 45 degrees sketch.

4. Assume that there may be un-smoothness at the unconstrained edges, and be prepared to trim it. In this case, the lower edges were good, but the upper edges showed some strange curvature within 0.3mm of the edge, which would be fed into the next surface if not trimmed back to a clean portion of the surface.

5. If a secondary constraint is required (for example, the subsequent surfaces), then use the above technique to get the edges close, then add the constraint. SW must then only make minor tweaks to force the alignment.

And voila:


Many sincere thanks to all who read and thought about this.

RE: Strategy for multiple curves at corner

(OP)
@rstupplebeen Thanks very much for that, it's a clear demonstration of the 'trim the cruddy edges' technique, which does not seem to get as much press as it should. It's also reassurance that it has to be done sometimes; I was concerned that I might be hacking to compensate for lack of skill.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources