Extend/Trim Arc bug

[etfrench]

An arc created from the end of an extended/trimmed line coincident with a circle is not coincident with the circle.

Model is attached

Video is attached

<iframe width="640" height="590" src="https://screencast.autodesk.com/Embed/Timeline/23d8dbb5-deed-44e1-bb31-c043636e6ab6" frameborder="0" allowfullscreen webkitallowfullscreen></iframe>

 p.s. Forum software doesn't like to embed screencasts.  Here's the url: https://knowledge.autodesk.com/community/screencast/23d8dbb5-deed-44e1-bb31-c043636e6ab6

[Beyondforce]

Hi @etfrench,

In the end of the screencast, you had no Tangent or Coincident constraints. Which is why the whole arc was trimmed.

You should have re-created the Tangent between the Arc and the Circle after you extended the Arc line! This way, you could have trimmed it without trimming the whole Arc.

Cheers / Ben
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[Beyondforce]

Btw, is this sketch is for one body?

[etfrench]

It still looks like a bug to me.  When trimming or extending a line, Fusion 360 looks for any crossing lines (or circles, arcs, etc.) and breaks at that junction.  There is clearly a junction here.  Workarounds are OK, but bugs should be fixed.

Yes, it is for one body.  Eventually it will be a 3d printed goniostat.

[Beyondforce]

I thought so too in the beginning that it was a bug, but it's not. It's just the way F360 works! In this situation, you must tell F360 that the Arc is Coincident (to create the contact) to the circle, and Tangent to the circle. A Tangent by it self doesn't mean, that there is a contact between the two lines, they are just Tangent to each other.

I know in Inventor, it works the way you described it, but not in F360. You just need to get use to it 🙂

Your model looks Great. Good luck building it 🙂

Cheers / Ben
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Check out my YouTube channel: Fusion 360: Newbies+

[TrippyLighting]

In general, try to avoid too much trimming.

Sketches in Fusion 360 behave much more predictable, particularly when driven with user parameters, when circles are left whole, for example.

That might make the sketch a little crowded in time.

Don't try yo much the profile you want to extrude 100%. In Fusion you can select as many profile segments as you'd like to create one solid feature.

[TrippyLighting]

The Form allows to embed screencasts quite fine.

Under the edit field for the post is another field "Paste a Screencast URL"

When you get your screencast ready email, you need to click on the link to the screencast in that email and once it comes up in your browser, the URL from the browser needs to be copied into that field.

Then you can click on preview, and then on insert.

You can also embed Youtube Videos.

If you copy the html code from the Embed tab in the youtube video page into the HTML tab of the Forum post that works quite nicely.

[jeff_strater]

Hi @etfrench, thank you for sharing the model and the screencast.

This one is kind of a gray area.  Both you and @Beyondforce are right in a weird way:  This could be considered a bug, or not.  This kind of geometry (two arcs tangent to each other) is actually a difficult case for sketch trim to handle.  The math gets tricky.  Do two tangent arcs "intersect" each other?  Mathematically, no.  But, I agree the expectation is that trim should detect and handle this case correctly.

I will enter this as a bug.  I'm not promising a quick fix, but it's good to have it in the system.

Jeff