As you know, 3D sketches could add up to 6 degrees of freedom for any rigid
piece of geometry. Constraints remove one or more degrees of freedom in
a model. Splines add a complex form of control to the curve. Coincidence to
complex surfaces will pose challenges to applying a coherent constraint scheme.
That does not change in SOLIDWORKS 2015.
Even with these considerations, SW2015 is a significant upgrade to spline on
surface. Users have requested that we add functionality to support split
- You can drag points along the surface.
- You can span multiple faces regardless of continuity.
I modeled a solid similar to the one you describe. I was able to fully define
the spline using a series of dimensions. While I was working, the spline never
became unsolvable or over defined. The key for me was to remove degrees of
freedom in a step by step approach to each dimension. That may not work for all
designs. I have attached an image of the model below.
R&D SOLIDWORKS, Modeling Applications Director
Just passing by here on the way out. I am not sure if your progressive constraining by dimensions would be that useful to a user. I see Mark was endeavouring to impose end constraints on the curve primarily and I think this is the way users would work at least for ID stuff. ie. they are deliberately constructing something in relation to other geometry but not necessarily wanting to define something mathematically in between as in an a turbine blade or impellor. Just a nice smooth curve on surface between end constraints. Possibly what you have successfully done would fail now if you tried to impose a tangent relation to another sketch. Look I dont have SW2015 so really this is not my concern but I will say there is nothing more aggravating than to repeatedly trip an unsolvable condition when working with a spline and to chase around trying to fix it ( those damned flipping spline handles also come to mind here) or remove some condition to make it work when it really ought to have anyway. Could there be a way to resolve the constraints ie suspend the failure and allow the user to nominate the constraint they would then prefer to cut some slack on to allow it to solve fully? Sort of like a knit tolerance. What I am thinking of is a different line colour for the suspended state spline and a symbol next to (or blue outline around) the compromised constraint which was nominated by the user.
Thinking about this some more...
First off I apologise if my previous post is confusing. I rarely express myself well as Mark will probably tell you after years of being confounded by my shared thoughts.
Put it this way - if you work with splines a lot you fairly often come across situations where they do become over constrained or unsolvable or flip out. From my experience where this happens provided you aren't doing something erroneous there actually ought to be a solution but the way SW attempts to resolve the equations it doesn't find it. I think Mark was alluding to this when he said the 3d solver is *limited*, and I would also add spline handle solving to that. From the users viewpoint this is frustrating because it prevents you doing something you really would like to do or from working intuitively. Sometimes there is no alternative but to abandon your endeavour or settle for a suboptimum solution say where you have to give away a constraint you really wanted. ID people love their end constraints and swoopy curves. Occasionally I have been so stymied by these issues I have started my models over another way.
Rather than be in this situation where SW balks at finding the solution because the coding is not smart enough to recognise a workable situation, perhaps we the user who know our intent could intervene and ease the problem. This could mean relaxing our intent a little at a place where we are more happy to do so, so that the maths can resolve. In this manner we are getting around the limitations of the solver by intelligent manual intervention or determining priorities. I guess this amounts to saying give me your best solution that works if I allow you some tolerance at this point but still endeavour to satisfy my constraints. This is not ideal but it at least it makes for the possibility of progress whereas otherwise you make none. In the case of flipping spline handles it ought to be avoidable by better logic but if it isn't then give the user an easy mechanism to intervene to get what they intended. There is nothing more frustrating than to keep battling a spline that wont yield to your will.
Be interested to hear from others what they think/experience.
I should add too that my splines frequently go not fully constrained. I don't think for ID purposes I would ever define my spline in the fashion you did above purely with dimensions. I would be more interested in end constraints, a minimum of internal points, spline weights and handle directions to arrive at some swoopy nirvana. I am not sure if you were endeavouring to precisely describe say turbine blade geometry you would do so in the manner you used either but perhaps you could.
Listen to Mark and Neil; they know whereof they speak. I don't know what your background is, but SolidWorks really needs to have someone with an ID background and real work experience to interact with the folks setting product requirements and writing code. You used to have a guy like that, but he quit. for us, for him.
I would suppose Ditmars has taken over from Mark? Probably this is the first time Mark has been on the other side of a complaint about usability and encountered dealing with the 'firm'. Usually SW people are reluctant to admit flaws in their program or announce any future directions and this can leave the user nonplussed for providing feedback. I hope Ditmars silence since his reply here means he is reading and taking note of how splines and splines on surfaces get used by the user in reality and considering some enhancements or revisions to the solver.
Just catching up on this post....
Neil and Jerry,
Ditmars is a very intelligent and thoughtful guy. He did not take my place in any way but I and other PD's worked with him regularly. He is not a PD (Product Definition Specialist) but rather the director of the entire modeling team. Previously, he play an important role for sketching. I have the upmost respect for him and of the people that interacted with at DS/SW, he comes to mind with fond memories. He was an important contributor and driver on the Style Spline which was a huge project and, I think, a great success.
I see the improvements in the 2015 SOS but I still think it has a ways to go. I suspect that it still needs improvement because of the limitations of the constraint system even thou I realize that by nature of being "on surface" this imposes some further limitations even over the standard 3D sketch spline.
Slow mail in your neck of the woods...
It sounds as though it doesnt work well enough to be of practical use and if thats the case you are quite right to draw attention to it.
Having been on the inside you know the people and the process and will be a little more tolerant than those of us who get exasperated with it and have to justify the obvious to the incredulous.
Thanks for raising the issue.
oh and by the way I hope your new job is going well and a Merry Christmas to you. Possibly I left that wish a little late and you will receive it in Feb but hey its the thought that counts...
A am enjoying my new job - thank you. I forgot how much I miss designing and engineering products. Working with a great team of people and working on some really small stuff (wearables) - Haven't done something larger than the palm of my hand for the last 11 months....