how to make a line tangent to spline

[Anonymous]

I cannot make a line tangent to a spline.  Is there a workaround?

Attached is a simple example of a fully constrained spline I need to make tangent to a vertical line.

Thanks.

[jeff_strater · Accepted solution]

Unfortunately, Fusion does not yet support a general "tangent to a spline at any point" constraint.  The closest you can come is to add a new fit point, and make the line and the tangent handle parallel, then make the fit point coincident to the line:

[Anonymous]

I ran into this limitation as well and have to say it’s quite perplexing. Every CAD system I’ve used over the years supports tangency to splines. I’ve also noticed that sketch fillets don’t work on intersecting splines. Are sketch tangency improvements planned for the near future?

[angrdnsr]

I'm having a similar problem.  I have a circle and curved spline, which I want an arc tangent to both, how would I do this with the tangent to spline function being available?

[rodrigo.alvarez]

Following this thread.

I wish these issues yet-to-be-implemented were marked as "Pending" and not "Solved" so that it would be immediately clear from the Google search results that there is no solution, and that it is an active ticket being considered or in progress. 

[chrisplyler]

Well, the question asked was, "Is there a workaround?" A workaround was given. So technically, this thread was solved.

That's how logic works.

[Anonymous]

It's not really even a workaround, if you project a line to a sketch it has no handles so it's impossible to do this. This really kills any interest I had in this program. Waste of time learning to use Fusion 360. I've tried doing some stuff I normally do in Catia in Fusion 360 and it's pretty much impossible. Fusion 360 is way too limited. At least it looks nice. Even Rhinoceros lets you make splines tangent with other lines/curves. So disappointing.

[Johnc911]

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@Anonymous wrote:

...if you project a line to a sketch it has no handles so it's impossible to do this.

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But that's the point of adding the fit point, you get the handles with it.

[laughingcreek]

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@Anonymous wrote:

...I've tried doing some stuff I normally do in Catia in Fusion 360 and it's pretty much impossible. ...

Apples and Oranges.  Given the price difference, I would hope you can do more with Catia.

[Anonymous]

The workaround is ok, but really does't solve the problem. The utility of the tangent constraint is it FINDS the point of tangency precisely. Sure, you can eyeball it and get close, but that's not a complete workaround, which is what we have.

[Anonymous]

Hi All,

Glad this topic might be coming back to life because I agree with David, the "workaround" is way too arbitrary to be considered a solution, and it doesn't work with control point splines or projected splines...

However, Chris, it looks like you posted a better solution back in June 2018.
Your solution was specially for a circle tangent to a spline, but you can easily use the same logic to make it works with line tangent to spline, see the picture attached below.


However, I'm having a very hard time making it work with control point splines...it either gets (falsy) over constrained or I can't move the construction around the spline...

Surprisingly tho, if I build the spline first, and then build/constrained that tangent on a second sketch, then there is no problem at all...very frustrating, since it's not always possible to split the sketched constructions...

One way or another, it would be really great to have it working with a simple constraint and any type of splines, especially since most CAD softwares can do it for years now...

[chrisplyler]

That video was a joke. The circle is not actually tangent to the spline at any point where the curvature of the spline between the center of the construction to the "feeler" point on one side is different than the curvature of the opposite side. Which is MOST points along a spline like that. The smaller the width of the "feeler" construction, the more accurate it becomes, but of course you can't do it at all with a "feeler" structure of zero width.

You can make the "feeler" construction pretty small, and make it close enough to fool everyone who hasn't realize the truth explained above. And that's exactly what I did to fool everyone in a thread about this same topic. A few posts later in that thread I came clean.

The same is true of your construction of lines.

The only workaround that even keeps it close (at least as close as Fusion can calculate the offset of a complex curve) is to just Offset the spline the radius of the desired circle, and then make the circle center point coincident to that offset.

[Anonymous]

Arff, why still having misguiding tutorial on official Autodesk online platform...the link I shared is not part of any full discussion disclosing how this is wrong...

After double checking your explanation using Solidworks, it seems like you're right, if you can afford a very short "feeler" (line parallel to the tangent in my drawing, connecting the spline at both tips) then you can have something very close to the true tangent... (Note: It seems almost impossible to have a zero width feeler.)

So then the best workaround would be to build that tangent circle like you presented it with the offset feature and then make a tangent line to this circle, right?
Edit: Well unfortunately it doesn't seem like it...once again Fusion 360 reacts like it is over-constrained, even though it's really not...also at the moment I add a line, and make one of the tip coincident with both the spline and the circle, it stops moving for reason I don't understand...

[chrisplyler]

My prank video is hosted on Autodesk's official site, yes. I had no idea it was being presented as an official tutorial. I certainly didn't intend that. Here is the thread I originally posted it in: https://forums.autodesk.com/t5/fusion-360-design-validate/open-letter-to-dev-stop-integrating-new-fe...

If you scroll down the post #19, you will find my reveal.

Is Autodesk just listing every single Screencast video anyone has ever made and presenting it as a tutorial? Seems overly optimistic on their part.

Anyway, I too get the glitchy "overconstrained" and unmovable behavior you describe. I cannot even reproduce my fake-tangent construction anymore like I did in that video. Of course that was made several updates in the past. Something has changed in the software.

[hoegge]

Well, isn't it about time to make those tangent and perpendicular to spline constraints possible? @jeff_strater Both are very often needed and a pain to try to work around.

Best

Hoegge

[Anonymous]

It would be funny that it's still not implemented, but it's too big pain in the backside...

Going back to solidworks on top of essential features not implemented interface is backwards. 

in 3 hours trying to do 5 minutes job exhausted my yearly swearwords limit..

[luca.scalea]

No solution on a 3 years old problem ? That's how I go back to Solidworks !

[clementPLHPN]

Yes, unfortunately, Fusion360 is still the most affordable parametric software I know of, but it's really lacking some essential features...

@jeff_strater any update?

[jeff_strater]

no update to report.  While we appreciate the frustration that this causes in some cases, it is still a relatively low-frequency problem for a large percentage of our users.  We'd love to fix every single deficiency, but it takes time, and we have to prioritize the use of our development teams' resources.  Sorry if that is disappointing, but that is just the reality of the situation.

[TrippyLighting]

@jeff_strater I've complained about this before and still find that this is justified, however as so often I have discovered that the solution to many problems is a bit of resourcefulness and application of the other tools available in Fusion 360.

As such I can create a sketch in Fusion 360  with an arbitrarily shaped spline with a line at an arbitrary point on the spline always being perfectly tangent to that spline.

I cannot create narrated tutorials at work, so this has to wait until tonight 😉