How can I edit "arc of ellipse"?

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sjb
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Joined: Thu Apr 27, 2017 10:40 am

How can I edit "arc of ellipse"?

Post by sjb »

Hi,

I think "Arc" can be edited, but what about "arc of ellipse"? This link
https://www.freecadweb.org/wiki/Sketcher_Arc_of_Ellipse
Suggests its all done by super-precise clicking.

Having created an (approximate) "Sketch → Sketcher geometries → Create an arc of ellipse",
RoughArcOfEllipse.jpg
RoughArcOfEllipse.jpg (20.02 KiB) Viewed 1764 times
I eventually want to make the arc "correct" - an actual length for the minor/major radii, an actual exact angle, and a way to define rotation. So, I need to rotate the ellipse about a normal to its centre, move the centre then edit the arc angle etc

What I'd like to do is use an edit dialog. I thought maybe if I used Draft WB, an Editor would pop up.

I appreciate that "sketcher" is not used for exact, measured elements, just relative angles etc.

Here is my aim:
1. Create an "Create an arc of ellipse"
2. Later on, edit it

Obviously, it's easier to get precise results with edit boxes or up/down controls than it is to hand-draw a "right first time" arc.

Regards
Stephen
jmaustpc
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Re: How can I edit "arc of ellipse"?

Post by jmaustpc »

Add appropriate constraints, like any other Sketcher geometry, ..... are constraints not working on arc of elipse for you?
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NormandC
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Re: How can I edit "arc of ellipse"?

Post by NormandC »

Hello Stephen,
sjb wrote:I appreciate that "sketcher" is not used for exact, measured elements
That statement is totally wrong. On the contrary, the whole purpose of the Sketcher is to define geometry with the most precision possible, all in the 3D view. No edit dialog is necessary.

To define your arc of ellipse you need to toggle its internal geometry (the ellipse axes represented as blue construction lines) back to visible. It seems that you deleted them. There's an icon for that in the Sketcher toolbar to make them reappear.
Attachments
FC_Sketcher_Arc_of_Ellipse.jpg
FC_Sketcher_Arc_of_Ellipse.jpg (99.28 KiB) Viewed 1749 times
sjb
Posts: 60
Joined: Thu Apr 27, 2017 10:40 am

Re: How can I edit "arc of ellipse"?

Post by sjb »

Hello Normand

Thank you for your reply. Here, Sketcher Workbench, it says
The Sketcher moves away from this logic. Objects do not need to be drawn exactly as you intend to, because they will be defined later on by constraints. Objects can be drawn loosely, and as long as they are unconstrained, can be modified.
That is why I (mistakenly) thought "...sketcher is not used for exact, measured elements...".


I have now created a new sketch, and added an arc of ellipse. I can see the construction lines, but I can not see where to type in precise values.
...all in the 3D view...
Is this still within Sketcher?
No edit dialog is necessary
Can I type in values somewhere else - double-click somewhere first maybe?
EditArcOfEllipse.jpg
EditArcOfEllipse.jpg (142.94 KiB) Viewed 1710 times
Thanks
Regards
Stephen
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bejant
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Re: How can I edit "arc of ellipse"?

Post by bejant »

If using FreeCAD 0.16, in Part Design WB select the green line again in your screen grab, click a Constraint such as this one:
Image

A dialogue window will open, and you can type in the desired value:
20170501d.png
20170501d.png (20.63 KiB) Viewed 1703 times
chrisb
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Re: How can I edit "arc of ellipse"?

Post by chrisb »

I would strongly recommend to work through some of the tutorials - video or classical. They show how to use e.g. the Part Design Workbench. bejant has a link in his footer, give it a try.
It has turned out to be important that you actually work through the tutorials, it helps but is not sufficient to watch them.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
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NormandC
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Re: How can I edit "arc of ellipse"?

Post by NormandC »

chrisb wrote:I would strongly recommend to work through some of the tutorials
+1
sjb
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Re: How can I edit "arc of ellipse"?

Post by sjb »

Thanks all for your guidance.
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