Exploding UCS ?

[torbjorn_heglum2]

I have been fighting with 3D sketches again. Even if I now have learned to dimension to a plane to get directional dimensions, I still struggle to get stable and predictable 3D sketches.

So today I got an idea; - what if I placed an UCS inside the 3D skech and fixed it to some sketch elements? That should give me some planes and axes that could be used to constrain and dimension other sketch elements internally in the 3D sketch.

The result was really not as expected... instead of controlling my sketch elements, the UCS decided to disintegrate. Those planes of the UCS are definitely not orthogonal anymore.

Maybe this is a bug that is fixed in Inventor 2018?

Torbjørn

Inventor 2017.4

[jhackney1972 · Accepted solution]

I believe you are getting your issues because you are creating the new UCS while still in the 3D sketch.  You will not get this issue if you create your 3D sketch up to the point where you want to create your new UCS, stop it, create the UCS, then start a new 3D sketch and continue where you left off with the first.  They will merge together unless you select points within your original 3D sketch like I did in my screencast, this was a mistake.  Since the UCS is independent of the 3D sketch geometry, it will be stable and you can dimension off of it easily.

This, by the way, is a very good idea to control the location of 3D points which all of us struggle with at some point.

[JDMather]

My 3D sketches are anchored to 2D sketch(s), rock solid, easy and robust based solely on the BORN Technique.

I recommend that you attach a "completed" example here for suggestions on alternatives.

[hncarle]

Your problem stems fro the fact that the lines you drew are NOT perpendicular to each other.  They are drawn in what ever direction the line happens to end up. Your screen cast shows this quite clearly.

The best solution to this problem if you want to draw a set of lines to use as your ucs is to take each line an make it perpendicular to one of the major planes FIRST. Then you can use it as your origin in your sketchs.

[johnsonshiue]

Hi! The behavior does look funky! It is because the sketch is not yet fully computed. If you click on the Update button, everything will go to the right place. I bet you can reproduce the same behavior with a work plane without using UCS. This is why these Work features are removed from 3D Sketch panel since the compute sequence can lead to funny behavior like this.

Many thanks!

[torbjorn_heglum2]

Thanks for the suggestion. 

To split the 3D sketch in several sub sketches can be a functional workaround. I guess I will use this in a future project.

Torbjørn

[torbjorn_heglum2]

That's the workaround I use myself. The only problem is that more time is needed to make required workplanes & 2D sketches, the browser gets more cluttered and the design intent is more hidden. But it works.

Would have loved to see more predictive 3D sketches, that's why I am trying to find new workarounds. But this last one was definitely no success

Torbjørn

[torbjorn_heglum2]

Thanks for the reply.

You are right, the UCS planes do jump back when updated. But the sketch does not obey the constrains, neither dimensions or the geometric constraints. Still looks like a bug to me.

But this led me to a new possibility: Creating workplanes inside the 3D-sketch based on internal sketch geometry. They seems stable and behave as expected, and is functional references for directional dimensions.  

Thanks

Torbjørn