topic Spline has breaking changes? in Fusion Design, Validate & Document Forum

Spline has breaking changes?

wangxl00 — Tue, 31 Mar 2026 16:02:48 GMT

I have a fit-point spline created several months ago. And now draw a new spline in the same sketch, with exactly same parameters, but in latest version of Fusion 360.

Strangely the two splines are very different. Am I missing something?

(Left: old one, Right: new one)

Re: Spline has breaking changes?

TheCADWhisperer — Tue, 31 Mar 2026 16:33:47 GMT

@wangxl00

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

Betreff: Spline has breaking changes?

g-andresen — Tue, 31 Mar 2026 16:37:14 GMT

Hi,

I'm getting the image on the right.
Please share the F3D file so I can check it.

günther

Re: Spline has breaking changes?

wangxl00 — Thu, 02 Apr 2026 06:20:05 GMT

@TheCADWhisperer @g-andresen Please check the attached f3d. Thanks.

Version information: the original model was drawn on Feb 3 2026. The new spline was drawn today, on Fusion 2701.1.27 (macOS 15.7.4).

Re: Spline has breaking changes?

wangxl00 — Wed, 01 Apr 2026 08:04:05 GMT

I think this may be a serious bug of Fusion 360, because spline feature is so essential for 3D modeling. But not sure whether the old version or newer version has bug.

Can someone at Fusion 360 team look at this issue? Thank you.

Re: Spline has breaking changes?

jiang_peng — Thu, 02 Apr 2026 07:20:59 GMT

Sorry for the inconvenience! Please following the steps on the video, and I've also uploaded the updated f3d file. Please check.

Basically simply please "Deactivate Tangent Handle" for all 4 tangent handles of left spline, and "Activate Tangent Handle" for all of 4 and add controls to the tangent handles.

The better practice for the fit point spline is that:

Create the spline, position all the fit points
Add tangent handles if required, don't move the fit points any longer.

For a better control to the shape of the spline, probably CV spline is a better choice. Adding constraints and dimensions to the control polygon will precisely define the shape of the CV spline.

Thanks

Re: Spline has breaking changes?

jiang_peng — Thu, 02 Apr 2026 07:22:53 GMT

(view in My Videos)

Re: Spline has breaking changes?

jiang_peng — Thu, 02 Apr 2026 07:48:08 GMT

This is fixed design

Re: Spline has breaking changes?

et — Thu, 02 Apr 2026 18:24:35 GMT

There is definitely a problem with splines now. They are unusable. How did this happen?

Re: Spline has breaking changes?

TrippyLighting — Thu, 02 Apr 2026 19:12:55 GMT

This has been the case since the introduction of fit point splines more than a decade ago.

It isn't pre-se a bug, but an implementation peculiarity.

As @jiang_peng has already mentioned, control point splines are a better choice for this. They are also easier to dimension as you don't have to deal with tangent handles.