Ellipses: scr*ing up the design ?

[tormy.vancool]

Well i did use an ellipse on my deign because I needed its shape.

I trimmed it eliminating one side.

I applied an offset

I started to finish the work by applying some dimension.

But when I edit that sketch, to change parts of the remaining ellipse, the design brokes down; Really smashed.

No way even to constrain it. hen I try, everything goes to hell.

Are ellipses so cumbersome geometries in Fusion 360?

[jeff_strater]

"I trimmed it eliminating one side"

This is the problem.  Trimmed ellipses are not well supported in Fusion sketch.  Keep the ellipse as a closed curve.  There is rarely any need to trim an ellipse.

[tormy.vancool]

"Rarely" but not "none". If I used the Ellipse it's because the object I'm designing requires that shape.

I tried to use Splines instead but I got same kind of issues.

Here the shape. If I add ANY constraint or I try to do it, the sketch falls apart. All the craps you spot here, are my (failed) endeavours to stabilize that ellipse

I see the only one alternative is to design segments and then smooth them down with Fill but to constrain such stuff is a pain in the a**.

I'm stuck.

[davebYYPCU]

"Rarely" 

Tell that to aviation, marine and organic designers.

Trimmed ellipses are required in (Loft and Sweep) compound Paths.

[tormy.vancool]

Re-reading the answer ... is it a joke? it looks like Autodesk is not able to fix this issue after more than 40 years CAD experience (???) Sorry but this disappoints me quite a lot.

If a geometry is present MUST function in all its aspects. Stop! It doesn't exist "not well supported". It's not "FreeCAD" where programmers are working in their free-time. It's Autodesk. It's a major brand in CAD.

I hope somebody addresses this as quick as possible by releasing an update (not the major update ... not excusable to wait again 1 year of top the 41s ... a CAD like this shouldn't even be released with such issue.

BTW I tried to design that piece in Solid Edge 2023: it work without issues. But of course this is only 1 piece over many are composing the object.

IMPORTANT: Please don't get it personal. But objectively this is a big lack by Autodesk.

[TheCADWhisperer]

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@tormy.vancool wrote:

I'm stuck.

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@tormy.vancool 

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

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@tormy.vancool wrote:

BTW I tried to design that piece in Solid Edge 2023: it work without issues.

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@tormy.vancool 

Can you Attach this SolidEdge geometry here (in a neutral file format)?

Are you aware that there are two possible solutions for an Offset Ellipse (true mathematical ellipse or spline constant distance)?  I assume you want constant distance rather than true ellipse.

[tormy.vancool]

I also tried to delete all the ellipses and to remake it with only one. Same disaster.
I also tried by Splines. Same disaster.

So I imported the STEP on Solid Edge and I added the details I wanted.
But this is not the way to work. Ellipses must be working as any other geometry.

NOTE: I wouldn't want to upload the whole project here. I have to find the way only to give the part.

[TheCADWhisperer]

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@tormy.vancool wrote:

NOTE: I wouldn't want to upload the whole project here. I have to find the way only to give the part.

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I am interested ONLY in that sketch.

Recreate that simple sketch in a new dummy file that does not reveal any proprietary data.

The only reason I asked for the SolidEdge solution was so that I could see where you are going with this sketch.

If you could cut away all other geometry - that STEP might be helpful.

[tormy.vancool]

Ok super I found the way.

Please here the exported Sketch from Fusion 360

and underneath the .STEP created in Solid Edge

[jeff_strater]

If the same thing happens with splines, then I suspect it has nothing to do with support or lack thereof for ellipses in Fusion sketch.  As @TheCADWhisperer requests, please share a design that contains just the sketch here, as well as a description of what changes you made to cause the "disaster".  There are likely additional constraints or dimensions that can be added to make the sketch more well-behaved.

[tormy.vancool]

I already uploaded the requested files. but you said that the Elipse's trim is an issue ... to avoid it.

[TheCADWhisperer]

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@tormy.vancool wrote:

 it looks like Autodesk is not able to fix this issue after more than 40 years CAD experience (???) 

IMPORTANT: Please don't get it personal. But objectively this is a big lack by Autodesk.

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@tormy.vancool 

Trimmed Ellipse was solved by Autodesk long ago in their Autodesk Inventor Professional parametric MCAD software.

I would have to check my documents to check date, but I think I first wrote about this in 2007.

In any case - fully parametric trimmed Ellipse is robust and predictable in Autodesk Inventor Professional.

Please don't take it personal - but your Fusion sketch is a bit of a disaster.

There was no need to trim the Ellipse to create this geometry in Fusion. 

But that is just part of the issue.  You have used many other sketching techniques that I would not consider using in my work.

@tormy.vancool 

Are you willing to start over from scratch and do it my way?

Q1. Is there a logical reason you chose to have the Origin locate where you did - or are you OK with me moving the Origin location in my example of how I would model this in Fusion 360?

[tormy.vancool]

besides the fact I'm not the one that told trimming Ellipses is not suggestable but the software architect as you can clearly see here

So .. if they did solve in Inventor why in Fusion did they leave the issue??

However ... I'm certainly willing to restart it since it's only one of the many pieces but it's the only one not-editable.

yes it's the only one piece I didn't put in the origin. I needed up there to reference it to the other one pieces. And I think an error lead to another one and so on. But it MUST HAVE that shape. So we can start in the origin. Not problem, because now there are all the required dimensions and I will position the piece into its place once it's finished (extruded, filled etc)

EDIT: at the moment I don't see any example send by you. At least I don't see attachments.

[jeff_strater]

correct:  I did recommend not using trimmed ellipses, based on my own experience with them in Fusion sketches.  That is also why @TheCADWhisperer is recommending the same - leave the entire ellipse in one piece.  I thought you were looking for suggestions on how to improve the sketch.  This is one piece of advice I offer to anyone using ellipses.

"So .. if they did solve in Inventor why in Fusion did they leave the issue??"

I worked on both products, and both from the very early days.  Fusion has a different sketch solver than Inventor.  That is because the component used in Inventor is very expensive to license.  Inventor costs $5,000, Fusion is an order of magnitude less costly (and offers a free version).  We did not intentionally "leave the issue".  Ellipses (and more so trimmed ellipses) are not widely used in CAD designs (I am NOT indicating here that they should not be used, only trying to explain that this issue, while I see it is annoying you right now, is not a high priority at this moment).  I do hope that Fusion becomes better at this over time, but you should not expect a fix next week.

I suspect that your sketch has other issues, as @TheCADWhisperer indicated.  I will let him help you create a sketch which is more stable than your current sketch.

It is also possible that there are other bugs in Fusion sketch revealed by your design.  If so, we will log and fix those issues as we can.

[TheCADWhisperer]

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@tormy.vancool wrote:

EDIT: at the moment I don't see any example send by you. At least I don't see attachments.

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This is going to take some patience and back and forth discussion.

@tormy.vancool 

Q2. In the image below I have labeled four curves.  Which of the four curves (by number) is most important to your Design Intent. (Think about how the object is used in the real world. How it is assembled with other components, its function and how it is manufactured.)

[tormy.vancool]

All of them are important. Right for the way it's used in the real world.

Let's say the main curve is 1 AND 4 ... the internal ones are the derivatives to make that object 5mm think and to have the required notch where it depicted (in the picture you posted, there are 2 small circles but it must be the one and the way I designed in the original).

After have designed the geometry, I started to constrain it. But when it went to the "remains" of the ellipsis. I had troubles and I left it there,  since at that time the object was considered finished.

Then popped up another need that will improve some real stuff once is mounted.

So I wanted to add the 2 features you got on the Solid Edge 2023's file.

The first thing I tried is to constrain the Ellipse. I wasn't able.

Then I used a Spline to repeat the curves of the ellipse. I deleted the Ellipse of course and to have an help I have made a guide with a construction line.

Fine, then I removed the construction line (it did serve only for me optically, to be able to rebuild the curves with the same curvature). Vut when I tried to constrain the Spline, I got again troubles.

Then back to the Ellipse ... at that point I found myself in the corner. Because even designing only the curve 1 and trying to constrain it, the design fell apart.

I have remade the design in Solid Edge 2023: it worked without any issue and constraining everything.

then back to Fusion to understand what's wrong with.

At the end I came here.

[TheCADWhisperer]

@tormy.vancool 

Are you going to follow my instructions or are you going to try to fight this all the way?

I have a method that will not appear obvious at first glance until I prove that all previous work was rubbish. 

[TheCADWhisperer]

@tormy.vancool 

First we will start with some basic geometry considerations in Fusion 360...

Sketch the Ellipse shown below...

Now Offset the Ellipse selecting where shown (approximately midway between the vertical axis and the horizontal axis 20mm towards the outside of the original Ellipse.

Now Offset the same original Ellipse selecting the curve near the horizontal axis where shown below 20mm towards the outside of the original Ellipse...

Save the file with the original Ellipse and the two offset curves as instructed above.

Attach the *.f3d file here for next set of steps.

[TrippyLighting]

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@TheCADWhisperer wrote:

Are you aware that there are two possible solutions for an Offset Ellipse (true mathematical ellipse or spline constant distance)?  I assume you want constant distance rather than true ellipse.

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Three! You can always extrude a surface from the full ellipse, trim the surface, offset the surface, and if you really need  a sketch you can project the result back into a sketch. It's convoluted, but workable and parametric.

That also prevents the rather buggy sketch offset to interfere with the sketch.

[TheCADWhisperer]

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@TrippyLighting wrote:

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@TheCADWhisperer wrote:

Are you aware that there are two possible solutions for an Offset Ellipse (true mathematical ellipse or spline constant distance)?  I assume you want constant distance rather than true ellipse.

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Three! 

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@TrippyLighting 

You are getting ahead of me completely missing the point.

Follow my instructions exactly as written.

What do you observe. Based on this observation I will move on to the real solution - but first the geometry must be understood.