The spline from hell

[blacktip]

I'm currently almost having a panic attack when trying to bend those splines the way I want them to be bent, but it seems like (con)fusion 360 has it's own way to deal with splines. Sorry for sounding like a rant-meister, but I'm wondering if there's perhaps a Spline-101-course I can take in order to make things right?

Also, why does F360 complain about me not having enough clearance when changing the radius of a swept circle (i.e. making a tube) around the spline? I have triple checked that an increased radius *would* fit, but I'm still stuck with a too thin pipe. Besides, even if a too big radius would be set, wouldn't it be nice to have an option to allow intersections? I'm also wondering why there's no instant feedback/update of the tube in the viewport when changing an anchor point or bezier handle on the spline? 

I really would like the spline handling to be much more like inside Cinema 4D, where you have full control of the anchor points, beziér handles as well as being able to see a swept profile in realtime when changing anything in the center spline. Too bad that C4D Lite (that I own) doesn't allow for exporting models... and I really don't have time to learn say, Blender.

I'm attaching a screenshot of what I tend to think is a pretty easy spline + swept profile. All I want to do is to make the wristband lay flat on the ground + adjust a plausible bend of the wristband when it passes on top of itself.

happy cheers (after all),

Markus

[laughingcreek]

This may not apply to your case.  I frequently get the same type of error when sweeping a profile along a spline.  Sometimes pulling the extent of the sweep slightly back from 100% makes it work.  or straightening the end of the spline.  that final little bend at the end of a spline seems to give sweep trouble.

[blacktip]

Ok, thanks for the suggestions. I'll try and see if they apply to my issues. The main problems I have is to master the bends (i.e finding a quick workflow for editing, tweaking and positioning the XYZ-directions of the handles, ad well as the positioning of all points.

[SaeedHamza]

Hi,

In this picture below you can see the area that causes the intersection problem, but I suppose you already know that so ...

Here is a screencast to show you how to better control your spline, I hope it helps

Regards

[blacktip]

Hi Saeed, and thanks for taking the time to record that screencast. And yes, I am aware of how to place the points in order to make the path be bent in a natural way (having the pipe/sweep jumping over itself, that is). However, I have experienced many errors where the spline had a huge gap between any close connecting intersections, and still weren't able to create a pipe that was thick enough. Also, that are where the red circle you drew in my screenshot was placed actually had a pretty wide gap too, but due to perspective it looks closer than it is.

I actually have one question regarding your workflow: I used the Pipe-command, and I see you using the Sweep command. Is there any main differences between the both? Apart from (I guess?) being able to sweep any kind of profile along a spline?

[SaeedHamza]

The main difference between both of them is that the pipe command is easier to apply than the sweep, because a sweep needs a path and a profile, where the pipe only needs a path, but ...

It's important to remember that the pipe is only about circular sections only! where the sweep section depends on the sketch profile, and that's a huge difference

[laughingcreek]

Here's a short screen cast illustrating what I meant by shorting the sweep path to clear an error.

As far as work flows for creating a spline path like that, here is how I approach it-

-sketch spline points on the 2d sketch

-while in an iso view (like home) move control points into 3d by moving along the z axis only. Go back to top view to adjust XY positioning. 

-then I start fiddling with the tangent handle controls.  If  try to do this while in a 3d view (like home) I get lost!  so I will alternate between front, left and side views to adjust these.

Something to keep in mind with the tangent handle controls.  Before you edit one for the first time, their magnitude and angle will align themselves with the spline in a natural way when you move control points.  Once you edit a handle, it will stay in that angle and magnitude even when you move things around.  They can be "reset" by selecting the tangent handle and deleting.

[laughingcreek]

Also, the sweep command will allow you to put the profile mid line, instead of all the way at the end.

-This can help when the end condition of the line is what causes the problem

-you can put the profile sketch in a location that is easier to see if there is a lot visually going on at the ends.

-you may not want to sweep an entire path in both ways, sweep will let you do that without having to break the path to create a start point.

[TrippyLighting]

---

@blacktip wrote:

...inside Cinema 4D, where you have full control of the anchor points, beziér handles ...

---

Splines in C4D just as in many other polygon modelers are beziér splines. However, splines in Fusion 360 are a different type of spline. This is also the reason why the two halves of the spline handles are always aligned, which is different (and very convenient) for Bezier splines.

Also you need to realize that the solid body you are creating is in general a NURBS surface requiring much more complex math than a polygon model. Thus it's more difficult to visualize in real time.

There is also no reason why you could not model the hose in C4D as a quad mesh and then export it as a .obj,  import it into Fusion 360 and convert it to a T-Spline. Then you can still fine-tune the T-Spline.

[jeff_strater · Accepted solution]

Sorry, I'm coming late to this party.  Just wanted to add a quick note about self-intersections.  As you've no doubt realized now, Fusion sweep will not allow self-intersections.  There is just no way around this, unfortunately.

There can be two types of self-intersections:  Where a bend in the path is just too sharp that the profile can't make it around the bend without hitting itself.  For instance, this pipe succeeds at a diameter of 4.9mm, but fails at 5.0mm:

The only way to fix these is either a smaller diameter pipe, or changing the bend to have less curvature

The second is, I think, the one you ran into - a self-crossing path, where the sweep from one section interferes with the sweep from another section:

This one succeeds at diameter 11mm, but fails at 12mm.  This one you can get around by taking advantage of a simple trick:  The limitation is that the sweep cannot intersect itself.  But, it can intersect any other body.  So, you just do it in two steps.  You do have to use Sweep to do this:

Jeff

[blacktip]

Thanks for this information. I actually only used the Pipe-command for this, but I might trying out a regular sweep the next time an see if things get better.

[blacktip]

Hi, and thanks for this info regarding the differences in splines versus other modellers. I wasn't aware about the more complex dealing with these inside F360 (although it 

would be nice to have a better overview and feedback of what's going on) 🙂

I just yesterday realized that I can't export anything from C4D Lite (which comes with the subscription of Adobe's products). So, there's no (legal) way fot me to use C4D in order to create specific pieces of geometry.

[blacktip]

Hi, and thanks for these examples. I actually think I ran into the first scenario a couple of times (where I had a LOT of clearance but the pipe still wouldn't be as thick as i wanted). Anyway, I eventually made a wrist strap that I could live with, and added that to my camera model. Now, trying to master lighting and ray bounces... Attaching a test render i made this morning. 

Again, I'm really baffled by all tghe response that are given from other users in this forum. You all rock 🙂

[TrippyLighting]

Some nice rendering there!

[blacktip]

Thanks. I really need to read up on lightning, textures and ray bounces, but eventually I'll get there! Render made in Keyshot btw. 

[TrippyLighting]

Not sure where the video went on this class recording at Autodesk University class , but I had the chance to attend in person. Excellent class!

But the class materials are also very good reading material!