Scaling fit point spline; strange handle behaviour

[Anonymous]

I'm trying to scale a fit point spline (drew it on top of an image, but I want to make it bigger keeping it's proportions). When I perform the scale using the modify -> sketch scale tool this happens:

Is this expected / am I doing it wrong?

Sorry if it's a noob question, just have been playing with Fusion 360 the past few days.

[jeff_strater]

in general, spline scaling works.  Could be something specific to your spline.  Do you have any tangent handles enabled?  Any constraints that are not obvious from the video?

[TrippyLighting · Accepted solution]

Well ... I though I had seen that behavior before and tested this out.

If you create a "virgin" spline and don't touch the tangent handles then it works fine.

However if you edit/change a tangent handle the spline behaves as shown in the screencast.

[Anonymous]

Thanks for the help both of you!

I just tested it myself on a fresh scketch, you are absolutely right. If I just move the handles circled in green scaling is working fine, but if I move the ones circled in red the same thing happens as posted in the question.

Do you guys know if this is a bug or expected behaviour?

[wmhazzard]

It looks like control point splines scale, modified or not. I would think fit point splines should work the same way. 

[Claus_J]

Jeff, has this been logged as a bug? I have the same problem, it makes no sense.

Claus

[jeff_strater]

yes, the internal number is:  FUS-58081

[Claus_J]

@jeff_strater  does this bug have any kind of priority? it’s not a feature request or some exotic suggestion but a real, nasty bug that has been around since 2016. These kind of things are why I could never use Fusion as my primary cad app. The app I mostly use is by a smaller developer and he would honestly fix such a problem within days, even hours. 4 years and counting...

Claus (paying subscriber, not hobbyist) 

[jeff_strater]

If you are looking for an honest answer:  Probably no.  To be honest, scaling fit point splines is just not that common of a workflow.  Yes, this is a bug, but we have limited resources, so we have to prioritize the fixes.  I understand the outrage, but the reality is that there are many such "nasty bugs" in Fusion, and we just cannot solve them all in "hours".  The time at which a bug was discovered (2016) is just not a factor in that prioritization, and I agree with that.  Sorry not to have a more acceptable answer, but I assume that you didn't want a "yes, we will prioritize a fix for that", answer unless it were true.

[Claus_J]

I appreciate your honest answer. The other day I made an extruded object, a commercial project. After checking the shape was almost perfect but just a bit too mall. So I upscaled it 105% which basically ruined the fine tuning of the profile I had done, because of the bug. I don’t feel my workflow is broken, this should be the advantage of CAD, computer aided design as opposed to modelled in clay.

Anyway, and sorry for ranting, I suggest Autodesk transfer funds from marketing, wonder if anybody actually extract data from all those surveys.

Claus

[Claus_J]

I could not leave this alone, the fact that you let this bug hanging around makes me speechless. So I figured out a workaround. It seems if you constrain the spline points to a multiline you can still edit the spline as normal - but when scaling you deselect the spline and only scale the lines it's constrained to. In the attached video I show the concept. Notice the spline keeps its shape in the first section but deforms when the spline itself is scaled. This kind of torture should not be required to operate a simple function but it works.

EDIT: It works even if you create the spline first and the lines afterwards, which actually make it an easier workaround than I thought.

[Claus_J]

Every few years I wonder if somebody cared enough about this bug to actually fix it. I'm not a programmer but how hard can it be? Clearly an unedited spline scales fine but if you make an edit and scale afterwards the spline becomes broken. As I see it a value that controls the spline handle becomes scaled while it should not. How can you justify not fixing this?

Claus

[josiehaddy]

I cannot believe this is still an issue in 2024. I am using the free trial, and I won't be purchasing unless I can scale edited sketches. What is the point - I'm never going to create a perfect 1st-time fit point spline sketch. 

[Claus_J]

This bug has been reported since 2016. While I pay for and use Fusion for the odd job my preferred cad solution can't do, I check in once in a while to test if one day I can use Fusion for real work. I just checked todays update, still not solved after 8 years.

[g-andresen]

Hi,

This statement would not be made if you had studied the characteristics of tangent-based splines.

For me, the scaling function is the most dispensable function in parametric CAD software.

günther