Hi Morten, so looking into this more, the previous answer I gave is not correct.

Although it is true that the spiral/helix goes through a kind of fitting process, the end tangents of the fitted curve are being specified precisely, and it is the correct result to not have a tangent that agrees with a circle when you have a spiral like that.

It's not supposed to match a circle's tangent, even at the end because the spiral's shape is continuously shrinking and morphing to a different size, like Steve mentions above.

It would only have the same tangent as a circle if it behaved the same as a circle in the immediate vicinity of the endpoints. But a circle does not have the continuously shrinking aspect to it while the spiral does - any movement from the end of the spiral, no matter how small, results in a point that is not at the same radius as the start point. So that also means it does not have the same kind of tangent as a circle would at that point. The spiral is by its nature a sloped kind of shape, so it produces a sloped tangent as well.

I also tested this with Rhino and got the same result as well, just to verify that it was how the end tangents of a spiral was expected to be formed and not something unique to MoI.

So if you want to have different end tangents than what you are getting with a sprial, that means you actually don't want an actual spiral shape or at least not of that kind that is being produced there.


You may want to do something more with a freeform drawn curve with control points instead.

Maybe you could show a sketch of the kind of end result that you're looking for.


- Michael