Create spline tangent to surface

[Anonymous]

I've been trying for hours to get something seemingly simple. I want to create a bended pipe, but it's not going well. I only need one more part of the pipe before I can mirror it and finish the whole solid.

I can't seem to create a spline tangent to two axes. one side is tangent, but I can't seem to get the other side tangent to the axis coming out of the pipe. I've attachted the partfile and a screenshot of the area in question.

Hopefully you can help me out because I'm completely baffled by this. I've tried dozens of ways to create this last piece of pipe, but nothing seems to work. Why doesn't it work like in 2D sketches?

[johnsonshiue]

Hi! The arc you are trying to constrain is not a spline. Constraining in 3D is indeed quite different than in 2D. The key is to reduce degree of freedom (see attached part). I am able to get desirable result by creating a workplane between the two long legs. Essentially, the arc is only allowed to move on the plane. I do see some interesting tangent behaviors. It looks like the extension of the arc is also considered legitimate for constraining purpose. It is confusing. I will work with the project team to understand the behavior better.

Many thanks!

[Xun.Zhang]

Hi,

I seems cause by the less-half chord and more-half chord predict algorithm, so it's better to limit the current position as the intends such as the less-half chord in this case.

Try the steps in the video, hope it helps!

[Scott_Parker · Accepted solution]

Hi,

I think Johnson and Xun are looking at 3D Sketch8.  But it looks like you are concerned with 3D Sketch10.  The problem is that the axes don't intersect and you are working with only 3 control vertices for the spline.  It is impossible to create the condition you are looking for with 3 control vertices.  The first and last leg of a control polygon control the start and end direction of a spline.  With 3 points you can't satisfy all the constraints since you only have 2 lines in the control polygon.

To fix this problem you can insert another control vertex.  If you "Right Mouse Button" on the spline and select "Insert Vertex" you will get another control vertex.  You can then do a collinear constraint between the axis and the control polygon.

Hope this helps.

Thanks,

Scott

[Anonymous]

Hello. I was indeed talking about 3d sketch 10. I thought that would be clear from the screenshot I added. The feedback on 3d sketch 8 however was very helpful.

Inserting another control vertex worked brilliantly! Thank you so much for the help.