why does sketch act this odd way?

[cekuhnen]

and another video with some edge blending and lenght problems I dont understand why they happen

https://drive.google.com/file/d/0Byzv_NlyKp_2ZmRPaVlaNnNqdVU/edit?usp=sharing

[innovatenate]

I think there are a mix of things going on here. I think I have some advice that may help. Below is a ScreenCast I recorded for Inventor. It's not totally relevant for Fusion 360 since some the command I use in the video do not exist in Fusion 360. However, the same principals may be applied to help control the behavior in sketches in Fusion 360. At this time, the branch doesn't fall far from the tree. 🙂

I suspect the issue here is there are numerous degrees of freedom (DOF's) that are undefined for sketch figures. When you are "freeform" sketching by dragging around sketch figures with few constraints or dimension, it may lead to some unexpected behavior. In other words, the sketch solver may be solving things in a different way than you would prefer. The sketch solver is always looking for an opportunity to automatically create constriants and relationships between sketch figures. This can add to confusion. For splines, each spline fit point has a curvature and a tangent handle. Each has thier own set of DOF's to work with and presents an opportunity for precision control.

Another approach may be to add dimensions or constraints to drive the sketch figures into the position you'd like. With Inventor, it is common for users to fully define a sketch before moving using them in commands. Another thought is you may add enough constriants and dimensions so that the available degrees of freedom are limited to the ones you are "freeform" exploring. In this way, you will be then removing degrees of freedom while positioning the sketch figure to your liking and preventing sketch figures from moving in an unexpected way. 

I hope this suggestion helps. Let me know, either way. 

Cheers,

[cekuhnen]

thank you very much for the video. I am very used to how curves work in Alias / Rhino and the idea of sketch constraints are appealing but it seems also to come with it's own mixed back of problems.

It really seems to me that this sketch solver is ideal for more linear designs but when you use also include splines the solver and / or interface acts in rather strange ways.

in the screenshot below you see one handle bar selected - that one is always prone to move in a funny sluggish way while the other can be adjusted just fine.