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My use case is a prominent smoothed out edge rounding with a large 75mm radius at the edges of a table. I can manage to meet my needs wit a sequence of manual operations, but that is not the point here!

As far as  remember there was maybe a way to create Class-A curvature continuous rounding in older versions of FormZ (I use it really for a long time starting with 3.x or so).

I am not sure if this was integrated in stitch rounding (makes more sense for Nurbs) or simple and controlled rounding. The purpose for me is actually to smoothen out the join of the radius shape and planar  surfaces to avoid the usual visible ugly "frontier" when the surface goes from planar to a constant bending. I the real world this is mostly smoothed out by professional modelmakers. In a complex CADCAM workflow it is not the best idea to do this manually both CAD and after milling.

I searched the FormZ docs, forums (old too) and the web but did not find any hints related to FormZ, maybe looking for the wrong term.

  • Class A Rounding
  • Curvature continuous rounding
  • G2 Rounding

I found the facetting schemas in the FormZ docs and rounding tools, but this seems it only affect visualisation. When playing with the options and exporting the rounded shapes as DXF and check in other software, I get just a plain stupid radius. Maybe I need to stop to "play".

Any hints?

You find some content on  "Curvature continuous rounding" in the context of SolidWorks, Catia and Alias, but the findings are rare.


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4 hours ago, vva said:

like this, what I found in the Affinity Forum:

@vva Can you provide a link to the Affinity forum? This option seems not to be in the current Affinity Designer Desktop UI, but Figma is mentioned. Can it be possible that the Screenshot is from another Software Application? In this post Sketch is cited here https://forum.affinity.serif.com/index.php?/topic/144496-ability-to-add-smooth-corners-to-rectangles/ they use the term squircle .

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Yes, it is implemented in "Sketch"

the radius i divided in 1 arc and 2 nurbs. 

I made the rectangle in "Sketch", saved as SVG opened in "QCAD" and saved as DXF and imported in formZ:


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I finally managed to find the rounding tool opions in FormZ that I had in mind.

I is the N-rounding tool in the nurbz tool palette.

There you can select the grades of rounding I expected. I now start to play around an come back here later.

One issue is that the origin object was no Nurbz object and therefore some conversion may be needed.



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AFAIK the best continuity to a flat surface is G1. G2 and above require some curvature in the surface to be continuous to.

You could convert a flat surface to nurbs then add barely noticeable curvature by raising the curvature handles slightly. For each level above G2 you will need to adjust additional control points to make a smooth transition. This is exceedingly difficult to do.

Some applications like ZW3D use conics for blends, which are much easier to control. Currently, FormZ does not have conic type curves.

ZW3D is quite expensive. Fusion 360 has conic curves as does SharkCad Pro (not sure about the ViaCad etc from the same developer) but in these applications, you will need to create a conic profile and sweep it between the boundaries.

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I indeed took the way to extend the curvature into the flat surface and used the G4 level. As you said it is a bit cumbersome but worth the effort if you aim at real world production with CAD/CAM. I had to adjust the control points by hand.

My usecase is a tabletop 2D contour shape.

The usual way in a prototyping workshop for furniture and even when eroding steel tools with copper master in tooling to handsand out the smooth blend between a "technical" radius and the surface. In traditional contour shape ruler copy milling and havig people with these skills around, this was an absolute acceptable solution to invest this time.

When you want to produce a production ready and reproduceable shape directly out of machining or create better realistic renderings (parts looking as if these real world skills were applied) it is worth to play around with these adjustments.

Every time when your guts say: This is an artificial image, one reason can be the missing of cool looking smooth blends.

One issue with 4th Grade in FormZ is the missing of adjustment of the reference radius. In FormZ you have to create a real radius helpline first, adjust the actual rounding shape and then scale it including extension into the planes to meet the expected radius by approximation. This is acceptable for square 2D base shapes when the same corner can be repeated 4 times after creation and you just need to optimize one part.

I agree that smoothing out full 3D shapes and lots of them is a different job. In this case I expect a complete different approach to tackle the challenge.

The red curve shows the smooth blend, the black one the mathematical radius (this is an inbetween step and not the final shape)


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G3 is useful for automotive applications where the curvature is manipulated to preserve continuous reflections.

Aerospace applications have used conics for a long time, perhaps now that computers are powerful enough to digest the math, 4th order curves might be appropriate on rare occasions.

For consumer products and furniture, G2 is about as far as practicality goes. The analysis tools in FormZ aren't going to help you much beyond G2.

Fusion 360 can get close to G3, but to really work with G3 you need to use Alias Surface (not the cheaper Alias Concepts) or software of a similar calibre.

What would be nice in formZ is for N Blend and other nurbs tools supporting higher orders to have numeric input for T1 and T2 magnitude. The sliders are almost impossible to manipulate even with a fairly powerful PC.

Higher-order curves are not going to produce better surfaces and without a full set of controls will most likely just introduce errors.

An affordable cheat to work with high surface continuity is SharkCAD Pro plus DarCorps AeroPack. While the analysis tools are pretty much the same as in FormZ you can match Rho values numerically between conic surfaces. This produced good enough results when I was working on wind turbine concepts and needed to create flawless surfaces.

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On 1/10/2022 at 3:31 PM, Jaakko said:

I really enjoy reading this level of expertise. Don't understand much though.  😄

Thank you and keep going.

Seriously. I was reading the forum and then logged in just so I could "like" bbuxton's post above. I appreciate the knowledge I get from this forum.

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Thank you for your kind comments.

Although intended for fusion 360 this video is a great help for understanding what it takes to get good transitions for rounds.

Smoother Transitions To Flat Surfaces in Fusion 360 - YouTube

In formZ using 'convert to nurbs' will split an object into nurbs surfaces. You can use 'nurbs extend' to set back each surface using a negative value. This does not work on planar surfaces so you should add some curvature by increasing the degree to 3 or more using 'nurbs reconstruct' and then edit the control points to make it slightly curved. Once the edges are set back use 'nurbs blend' to reconnect the surfaces before stitching back into a solid. You can also use sweeps to run a good profile around a surface. Form Z analysis porcupine plot will help you visualise your curve continuity for this.

Edited by bbuxton

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