topic Revolute behaves differently with lines and splines in Fusion Design, Validate & Document Forum

Revolute behaves differently with lines and splines

janus2 — Wed, 10 Jul 2019 07:48:47 GMT

Hello!

Probably just an optical problem but it confuses me a bit.

If I create a part with 360 degrees revolute and the profile consists of lines everything is OK.

When I use splines for the profile I see a visible line at the joint.

A bug?

Jan

Re: Revolute behaves differently with lines and splines

graham.goodier — Wed, 10 Jul 2019 08:20:29 GMT

Hi there,

Thanks for posting! Do you mean similar to the models below? (The one of the left being made with lines and arcs, the other with a spline).

This isn't a bug due to the fact it allows part of the body to be selected, i.e. the top/bottom point of the profile as a point - for measurement, joint references etc - or the line itself to show the length, or be used to create planes at a midpoint etc. Either way they allow multiple uses for the body within Fusion 360. Without the profile, it would be a lot more difficult to reference any point on the body.

If this answers what you were looking for, please select "Accept Solution".

Thanks,

Graham

Re: Revolute behaves differently with lines and splines

janus2 — Wed, 10 Jul 2019 08:33:48 GMT

@graham.goodier wrote:
Do you mean similar to the models below?

Yes! The visible lines may have advantages for measurement, joint references etc.

However, this would also apply to shapes with arcs or lines (which have no visible lines). What confuses me is the different behavior.

But surely only an optical problem.

Thanks Jan

Re: Revolute behaves differently with lines and splines

davebYYPCU — Wed, 10 Jul 2019 09:13:42 GMT

Try the Visual Style

menu, select Shaded.

Re: Revolute behaves differently with lines and splines

graham.goodier — Wed, 10 Jul 2019 09:53:02 GMT

It's purely because the geometry is different, where there are "sharp" corners or clear edges with lines and arcs, the spline has a smooth transition between points, so as mentioned, you can change the visual display to hide this arc for a different visual preference.

It's more of a 'exception to the rule' I guess, due to the nature of a spline versus the aforementioned differences and reasons for still needing points/lines to reference which are on a part that uses lines and arcs are easy to identify/utilise.

Hope that helps!

Re: Revolute behaves differently with lines and splines

TrippyLighting — Wed, 10 Jul 2019 10:17:57 GMT

@janus2 When you revolve analytical geometry, so sketches or edges created from lines and arcs, then the revolve operation will create analytical 3D geometry and as such that line will, not appear. Analytical geometry such as circles, lines ellipse, spheres, boxes, tori can be described by relatively simple mathematical formulae.

When a Sketch includes splines when revolved, extruded, swept or lofted, those will create NURBS surfaces which are quite a complex mathematical beasts. NURBS patches are controlled by a quadratic mesh of control points (CV) and have a beginning and an end. The line you see when you revolve such structures simply indicates the start/end of the NURBS surface. In a revolved object the surfaces are tangent to each other and as such the geometry is fine.

The line only shows up in the Model environment. When you render such an object it will appear perfectly smooth.

Re: Revolute behaves differently with lines and splines

janus2 — Wed, 10 Jul 2019 11:53:13 GMT

Thank you for the detailed explanations.

Now I have understood the cause and everything is fine.
The reason why I asked for this (only optical problem) at all: Whenever something is unusual, I try to get to the bottom of it. Otherwise it hits you all the harder later ....

This rule does not only apply to Fusion 360

Thanks again
Jan

Re: Revolute behaves differently with lines and splines

TrippyLighting — Wed, 10 Jul 2019 11:54:46 GMT

No worries, this is a very valid question that does actually come up fairly regularly!