Is there a better way to surface this corner?

SledDriver

I've been trying to find a better/quicker solutiojn to this problem.

The red corner is a loft with guides and is typical of how I want this corner surfaced - the resulting corner is nicely flat and then convex. But I had to construct guides to achieve this.

The blue corner is using a loft without guides and goes to an unwanted concave result. Any attempt to use starting conditions for the loft to improve this makes the loft fail completely.

I've tried Boundary Surfaces, but they don't allow me to use a vertex as one edge.

Any ideas out there?

Here is the job: https://cad.onshape.com/documents/811d54459ac0e34acb5f0716/w/ff4827813201dd299e77d606/e/8140101668a6056ad44be08c

eric_pesty

I'm not an expert on surfacing but I think this is actually a very challenging shape as you have straight edges with a small corner radius blending into some rounded faces but also going to a sharp.

I think you would get better results if you had a radius at the top as well instead of the 3 faces meeting at a point. That way you get rid of the sharp corner that is stopping you from applying tangency and the loft behaves better.





You can even use a boundary surface which gives you better tangency control:




https://cad.onshape.com/documents/952fd932b50e7c3752be8336/w/6f88297b3ca373a07bd85a53/e/b26a202ce47d8f267c40e055?renderMode=0&uiState=6424bcfdbd0c203c28a1d6bf

It is still an awkward shape to generate though so it will always be tricky to get it really smooth. I think if you sides were curved all the way instead of transitioning so abruptly from straight to curved it would help...

SledDriver

Thanks for your ideas. I get what you are saying, but the point of my query is that I want the sides exactly as they are - I don't think I'm asking too much. It is possible to surface it nicely as I have done with the red corner, but it seems the surfacing tools themselves cannot cope with this, so perhaps the answer should be that the tools need improving to cope with this situation.

I am aware that the curvature of my red corner is not perfect when examined with the curvature tool, but it is close.

This may be a complex shape, but it is hardly seems a shape which should be this difficult to surface. It's a roof shape which could occur on the corners of large vehicles for a start.

This is surely exactly the sort of thing which cad systems should help us with, and not hinder.

I'll have a play with some of your suggestions and see how that works out.

Surfacing to a vertex is something which needs improving, or maybe someone can show me how this is already possisble if I've missed it.

GregBrown

The issue is, as Eric alluded to, with the underlying curves. There is no way the loft (or whatever surface creation type you choose) can make up for that. The guide curves kind of helped, but were not the solution... Have a look at the curvature combs for your red surface:


The influence of the G1 (tangent) connection defined in Sketch 4 (and with a dependency chain to Sketch 5 andComposite Curve 7...) carries right throughout the loft, causing the large changes in curvature in both the U(red) and V (blue) directions.

It would be better to go back and recreate the Sketch 2, Sketch 3, and Sketch 4 to use Bezier splines that are curvature matched to their respective adjoining edges... 

From this basis of curves you will achieve a much better quality loft.

SledDriver

> It would be better to go back and recreate the Sketch 2, Sketch 3, and Sketch 4 to use Bezier splines that are curvature matched to their respective adjoining edges... 

Aha. Thanks for this. I will certainly give this a go.

Many thanks.

glen_dewsbury

Here's another way. Not perfect, but with some tweaking I think you can make it work. Not as many features either. Your feature list looks a bit long just like some of mine before I think it through and start over. LOL
There seems to be some repeating of sketches and composite curves.
Hope this gives you some useful ideas.
https://cad.onshape.com/documents/d478371e27e41b9edb8ddaf6/w/7b1ed3eefa0cdadf3425492c/e/612d14aa5f63bdec9f431454

SledDriver

Thanks. I'm working my way through all the suggestions, learning all the time.

nick_papageorge_dayjob

I have some experience with surfacing on a prior cad package at an old dayjob, but not too much with Onshape. So I can't at this time offer specific cad help.

That said, I'll agree with the others. You can't really get clean surfaces the way you modeled it, in ANY cad package. Even the corners that Eric made, you can see the light reflecting off of them doesn't look great, even in the screenshot, without any special surface analyzing tools. If this was for a car, the industrial designer would be fired, ha ha:) Now, if its for a 3d printer, it makes no difference.

Surfaces are built on curves. You have to learn the curves first, then the surfaces will flow better. Its also not just a matter of how to make the curves, but a matter of where to put them. I would usually hand draw on paper a design like this, and come up with a strategy of where the curves belong. Then the CAD follows that strategy. Since you have a rough shape in CAD already, you could even take a screenshot, print it out, and hand draw where you think the curves should be. Then, re-make the entire thing over from scratch using those curves and surfaces. Its important when you make the hand sketches on paper, that the entire design is considered together. Doing the top but skipping the sides, or skipping the corners, will result in what you have now.

Also, you generally want each surface to have 4 "sides", never 3. 3 will lead to many problems. (unless the new CAD systems have improved this?) What Eric did was transform you 3 sided corner into a 4 sided corner, and it improved it significantly.

Depending on how "clean" you want the surfaces, and how well you want the light to "reflect" off of it, will dictate the modeling strategy.

I'd recommend going through all the onshape curve and surfacing courses. I think there are 2 or 3 of each. The advanced ones were behind a paywall until just a few weeks ago. Now they are all free.

Happy modelling:)

SledDriver

Thanks for all your feedback. I will certainly look through those courses.

...later...

Just had a look through the courses. Do you have a pointer to the courses you mentioned. All the courses I am finding seem to be more help manuals about how to use each command/tool in onshape. What I need is something which explains the strategies and reasons I would choose one tool over another for particular situations - the thinking behind what is going on in onshape.

nick_papageorge_dayjob

SledDriver said:

Thanks for all your feedback. I will certainly look through those courses.

...later...

Just had a look through the courses. Do you have a pointer to the courses you mentioned. All the courses I am finding seem to be more help manuals about how to use each command/tool in onshape. What I need is something which explains the strategies and reasons I would choose one tool over another for particular situations - the thinking behind what is going on in onshape.

That's Industrial Design school. I'm a mechanical engineer, and was never taught that in school. My coworker who was a degreed industrial designer taught me 15 years ago.

Def go through the courses though, as they do show you the "how", and that may help you with the "why". The courses are video and excercises. Should take you a full day or so for each one.

eric_pesty

Most of the learning center does focus on "how" to use the tools rather than "why" use one tool over the other but I would start with the "surface modeling tips and tricks video" as it's a bit more along the lines of what you need:
https://learn.onshape.com/learn/video/surface-modeling-tips-and-tricks-in-onshape

There are also a couple really good videos from @Evan_Reese
This one is a great overview of curvature and transitions that is relevant to your specific model: https://www.youtube.com/watch?v=X714INhNYL0
And this paddle board grip video is helpful as well as far as describing how to approach surface modeling in Onshape, https://www.youtube.com/watch?v=IjcFotLmCx8

Beyond that it's really just about "CAD surfacing" in general and not specific to Onshape and there are a number of resources out there that discuss surface modeling that would be applicable to any CAD software.

SledDriver

Thanks to everyone for all the pointers. I'm excited to go through these tutorials.

S1mon

While they're not 100% transferrable to Onshape, I would also highly recommend looking at the Alias "Golden Rules" and "Theory Builders": 

https://help.autodesk.com/view/ALIAS/2022/ENU/?guid=GUID-A23E9E8C-6D6B-41AD-A0AB-3E98183FBC2E

https://help.autodesk.com/view/ALIAS/2022/ENU/?guid=GUID-366304CB-16FF-46F9-9F64-D7385358D855

SledDriver

Thanks

S1mon

@SledDriver

This one has been nagging me for a bit. So I finally dug in, and got this:




I definitely took some liberties with your original curves, but I'm probably within 0.5mm everywhere.

I'm looking forward to more improvements of Boundary surface, since it is often generating more reasonable surfaces that don't have such crazy control points as Loft. There are many places where this part is only technically tangent, but because the underlying curves are G3-ish, the results are decent.

 

EvanReese

@eric_pesty thanks for the shoutout.
@SledDriver I keep an eye on the video comments, so feel free to ask questions there.
@S1mon lookin' cleeeean! I've been having to stop myself from taking the time to trying this because I've got too much on my plate right now as it is.