Closing two connected arcs

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onekk
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Re: Closing two connected arcs

Post by onekk »

knightstreet wrote: Tue Mar 21, 2023 9:55 am So the shape is already closed. Why is loft complaining that the shape isn't closed? I should be able to loft the shape with the line right?
constrained will not meant "closed", it is a common mistake:

two point that share the same position are not connected between them, they simply have the "same position in space".

Difference is between what links one object to another.

When you have full constrained sketch it wil mean that simply point are not moving in relation one to another, how these point are "connected" is another matter.

Interesting concepts that will shed some light could be "wires" and specifically open and closed wire, But even distinction between Topology and Geometry.

CAD modelling is different from sheet and paper modelling.


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Carlo D.
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knightstreet
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Re: Closing two connected arcs

Post by knightstreet »

drmacro wrote: Tue Mar 21, 2023 10:02 am
knightstreet wrote: Tue Mar 21, 2023 9:55 am So the shape is already closed. Why is loft complaining that the shape isn't closed? I should be able to loft the shape with the line right?
You are confusing closed with coincident.

The physical proximity of the two vertexes does not constitute coincidence. They must be marked coincident. If they aren't marked coincident, then the solver does not consider the shape closed.

Your other constraints have locked the movement, so you can't see that the vertexes aren't coincident, until you deactivate one of those constriants (as shown by @chrisb )
How do you mark them as coincident?
drmacro
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Re: Closing two connected arcs

Post by drmacro »

knightstreet wrote: Tue Mar 21, 2023 10:21 am
drmacro wrote: Tue Mar 21, 2023 10:02 am
knightstreet wrote: Tue Mar 21, 2023 9:55 am So the shape is already closed. Why is loft complaining that the shape isn't closed? I should be able to loft the shape with the line right?
You are confusing closed with coincident.

The physical proximity of the two vertexes does not constitute coincidence. They must be marked coincident. If they aren't marked coincident, then the solver does not consider the shape closed.

Your other constraints have locked the movement, so you can't see that the vertexes aren't coincident, until you deactivate one of those constriants (as shown by @chrisb )
How do you mark them as coincident?
Select them and click the set coincident icon. (Point on Point) Image
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Shalmeneser
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Re: Closing two connected arcs

Post by Shalmeneser »

An arc has 5 DoF = center (2) + 1st vertex (2) + angle (1)

The last vertex need to be constrained with only ONE DoF.
If you chose Coincidence constraint with the other vertex, you add 2 DoF : overconstrained !

You constrain the vertex with :
* PointOnObject with the axis (1) or
* PointOnObject with the other arc (1) or
* Vertical (or Horizontal) with the vertex (1).
The 2 vertex will be mathematically coincident.

You encounter the same problem when redoing the same arc from ExternalGeometry.
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chrisb
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Re: Closing two connected arcs

Post by chrisb »

Because I prefer to have full coincidences on the end of the arcs I usually start with those.
For the center remain among others the possibilities
- make the radii equal, this is especially helpful when using external geometry
- horizontal
- vertical

I recommend to avoid partially overconstrained sketches.
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Shalmeneser
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Re: Closing two connected arcs

Post by Shalmeneser »

In my example, if the end of the arc was not on the axis, you could make the 2 end points coincidents.
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