Convert lines, arcs and circles to spline

[Claus_J]

There is an entry in the idea station with the above title. The suggestion has had the status “accepted” since 2015. The ability to join lines and circles and edit the shape of the resulting spline is not only possible in most programs but also needed in my workflow. Since the feature has been accepted I wonder when it will be implemented?

I’m still watching the development of Fusion360 because there is just something about it that feels right, but every time I try to use it I have to give up because I just can’t do the things I need to do. In addition most posts on this forum starts with “I’m new to Fusion” and it makes me wonder if anybody is using it for professional work?

[lichtzeichenanlage]

Working with Fusion 360 includes that you change your behavior. That's true for every new software you're using, just the degree differs.

If you're searching any forum, you'll find this "I'm new to xyz". That's part of the nature of a forum because often new users do have more questions than experienced users (btw. I'm a new user and a hobbyist user). But you're right: Knowing if it's used professionally is an interesting question. I've a strong feeling, that the answer will be 'to a certain size'

[lucasproko]

Hey @Claus_J,

Thanks for pointing out that Idea Station post. It appears as though it was changed to Accepted by accident many years ago. I have changed the status to Future Consideration since we have no plans to implement this functionality currently. 

That being said, I would like to learn more about your workflow. Specifically:

• What kinds of products to you typically design?
• Do you typically draw out rough outlines with lines/arcs and then wish to have more control over exact curvature?
• When you do this, do you typically select entire chains of sketch entities to convert, or only specific lines/arcs? 

Your question about many posts on the forum beginning with "I’m new to Fusion" and how that relates to Professional usage is a good one. As @lichtzeichenanlage said, many forums typically have disproportionate amounts of new users asking questions considering forums are an active place to get specific questions answered quickly. We're proud that our community is strong and people help each other out so much on here. You'll be happy to know that Fusion is used by plenty of professional organizations, but typically those users are more advanced and have less of a need to ask questions on here. 

Thanks!

[Claus_J]

Lucas, what a huge disappointment. This is such a basic functionality. As answer to your question I make consumer products and furniture. They are not (all) square with rounded corners but often involve fine tuned curved surfaces. My workflow is not linear, sometimes a product evolve and change during the process. So I might start out combining geometries in 3d, then extract a cross section and use that as a profile for a surface or a revolve. In that process I need to work with the cross section as one curve.

You can imagine designing a bottle, maybe you want it basically cylindrical with rounded shoulders so you start out with a profile consisting of a straight line and an arch. But along the way you decide to give some curvature to the straight side or smoothen out the transition between the side and the shoulder. This is standard design work and in Fusion it means starting from scratch and trace over your lines and arches with the spline tool.

Another use is when I design a curve, let’s say an “s” shape. I like to control the curves by using circles and connect them with straight lines, a trick to make sure the transition looks smooth. With the circles and lines connected and combined into a single spline I can now make small ajustments as needed.

Hope this explain why I need that functionality and I hope you reconsider adding it.

[chrisplyler]

I don't know much about any other software program. I also don't know much about other possible spline mathematics. But I do know this:

Even assuming your lines and arcs are all tangent, the way Fusions spline controls function isn't conducive to going from a constant radius to a straight at a single point. I don't think a single Fusion spline CAN mimic a straight line tangent to a constant radius arc. Ready to be shown wrong, but that's what I think.

[TrippyLighting]

I am always wondering what people mean when they put out that "professional" statement. In my experience over 8000 forum posts it very often means :

"following my professional workflow in my line of work with my established workflows". Everything else of course could not possibly mean professional.

I've also experienced many users stating that something is "basic functionality" based on something they use daily simply because it is provided by their chosen software tool. Yet it isn'y generally  basic functionality.

If you generally want to now know whether Fusion 360 can be used professionally, then the answer is Yes. I use Fusion 360 in my two main lines of work I am developing manufacturing automation concepts, budgets and proposals and it's quick top-down modeling workflow make that quite nice.

I also do freelance product design for a number of clients and Fusion 360 performs nicely in that area as well.

When I reach the limits of Fusion 360 I reach for other tools. 

In know other people use it professionally.

However, whether you can use it in your line of work, with your established work flows is another question. 

IMHO many people that ask this question looking at this the wrong way. What they are really asking is "Can Fusion 360 replace my current software tool ?"

Why would it need to ? It is free to use and evaluate and even the $300 annual subscription is so inexpensive compared to other tools it is constantly compared with that there is no reason not to use it alongside other tools, get familiar with it and see it grow.

[Claus_J]

Trippy, thanks for responding to this and many other threads. I love the energy and seriousness you put into it. I don’t think it’s a matter of price, I’m on a mac since 20 years and it limits my choice. I have my trusted software and I’ll probably stick to it. In the end it’s not the tool that makes the artist.

However since the first time I tried out Fusion there was just something that caught my interest. I started it 5 times before I proudly was able to create... a cylinder with some added detail. What a victory. After that victory I wanted to convert my free subscription to professional, guess what, I could not figure out how to do it. And that sort of summs up my problems.

So I respectfully disagree that just because this software is “free” you are not allowed to give your 5 eurocents of advice. I would like it to be my favorite software and I will (probably) continue to influence the direction it’s taking. What I don’t understand is probably the general concept: so you have the most crazy, sexy T-spline tool that allow you to go wild but as soon as you turn to 2d geometry you can’t even join a line and an arch? It does not make sense. I’m coming back just to play with T-splines, but the software will not allow me to get on from there.

Regarding if the program is used professionally I’m probably asking for trouble. So I excuse myself. Anybody working for money is a professional. And it’s not that important anyway. But with the resources Autocad is putting into this I’m just guessing they are looking into making this project profitable at some point. Which means people paying for the software. Personally I can’t wait for it to mature, it’s sooo close.

[chrisplyler]

What do you mean, "...join a line and an arc?" You want them to be joined simply so you can grab and move both together as a unit without having to select both of them?

[Anonymous]

I think this would be a useful feature if implemented.

One use I can think of is that if you had the ability to convert a sketch fillet entity to a spline you would then be able to add a smooth constraint.

[Claus_J]

Chris, by joining I mean converting the line and arch into a single spline with the exact same shape, but editable. I’ll be happy to give some examples of cases where it’s handy. Let’s say you create a tubular frame for a chair. You start out with some straight lines in 3d space and create fillets where it bends. Now you decide to make a slight curve to the straight parts. My current workflow would be to join all the lines and fillets and end up with a single 3d spline I could sculpt as I please. It would of course break the history of the original lines and arches.

[lucasproko]

Hey all -

Always nice to see a healthy discussion on interesting topics. I don't want to dive into the details on every point, but I did want to address one comment @Claus_J said. 

---

@Claus_J wrote:

...So I respectfully disagree that just because this software is “free” you are not

allowed to give your 5 eurocents of advice....

---

I don't think that @TrippyLighting or anyone was implying that because Fusion isn't as expensive as many other tools that you shouldn't be giving feedback to make it better. Our Product team constantly monitors the Forum and other customer outlets to ensure we are collecting sufficient feedback to make informed decisions going forward. However, I hope you can empathize that there are many many users of Fusion and many areas that we can improve so we have to be intelligent about which functionality to prioritize.

In terms of the original topic, I'd like to further understand why a conversion to splines would be significantly better than simply editing the initial sketch and manually adding splines to get the desired curvature. I just created a couple quick gifs showing how I would perform some of the workflows that you described. I know these are simple cases, but I'd like to hear your thoughts.

Replacing a line with a spline

Creating an S shape

Thanks!

[Claus_J]

Lucas, thanks for the nice examples how to get around the “limitation”. Of course it’s a matter of temperament, there are some fases of the design process where you want to constrain yourself and there are some where you want complete freedom. Earlier I used Adobe Illustrator to sketch profiles for that reason.

I still think my request is valid, what is the reason you can’t even join two splines? You can make their end points coincident and tangent but they can never become one spline. I can see the whole parametric issue but I think you are taking it too far, parametrics should be helpful, not a limitation.

I can certainly respect your priorities, you did a great job so far.

[chrisplyler]

Illustrator has some spline advantages over Fusion. You can drag either end of a control handle to different lengths. Heck, you can even convert a control point to a "corner" such that the control handles don't have to be 180deg to each other.

As I said earlier, I don't think a Fusion spline can even accurately represent a straight line connected to an arc. Lines and arcs are precise. Splines are not. I can't get one to do it. Can someone show me how?

[TrippyLighting]

---

@chrisplyler wrote:

.

As I said earlier, I don't think a Fusion spline can even accurately represent a straight line connected to an arc.  

---

No it cannot. Mathematically analytical geometry is much simpler to represent than an spline. It can be approximated, but then the user has to decide with what accuracy. If you need higher accuracy you need more control points, and maybe a higher order spline, but the resulting spline will be much harder to control manually.

That same applies to T-SPlines BTW. A T-Spline cylinder is not as round as a cylinder modeled with an analytical surface. The more segment you use (the accepted minimum is 8) the more accurate it will approximate a "perfect" circle.

However, precision is really related to manufacturing parts and then the question is how accurate would a CAD model have to represent something physical.

---

@chrisplyler wrote:

Lines and arcs are precise. Splines are not. I

---

That's not true. They represent different types of geometry but both can be precisely represented/defined by mathematical formulae and parameters.

Just as you can approximate a spline with lines and arcs given some tolerance, you can approximate lines and arcs with a spline.

[chrisplyler]

Okay yeah, splines are precise. I expressed my thought incorrectly. They cannot precisely represent a true arc and line combo. At least not the way Fusion has them implemented.

[Claus_J]

Trippy, I always love your input, it’s so precise and to the point. I read another discussion for another software that they warned about the difference between a spline “circle” and a mathematical circle. Apparently it’s quite different. In my world, which involves quite some experience, it’s not that important. Whatever I draw gets interpreted by engineers anyway. Honestly, I even had manufacturers print out a drawing on paper and trace it by hand. Mind you my drawing had 3 decimals on it, can you imagine?. And the product turned out fine anyway. Of course this kind of sloppyness is what makes space rockets explode. But as long as you know you approximate you’re fine. For that reason a circle that’s called a circle should always stay true to the definition. A circle that’s been converted should be called a spline.