Tangency constraint not working on 3D spline?

[Art5]

In another thread that I started, I was trying to use loft and rails unsuccessfully to create a patch. I was told to make a 3D sketch of a spline and use tangent constraints to make it tangent to the two edges, thus defining the fourth edge of my patch. I've been able to do this successfully many times, but today it won't work for some reason. Anybody have any ideas why?Tangent constraint applied, but doesn't change the spline...

[TrippyLighting]

Yes, it's a bug that can pretty much stop you in your tracks when working with surfaces. We (@cekuhnen and myself and likely others) have reported this several times dating back years but it still creeps up al too often.

It might even go so far that it allows you to create the constraint and then you cannot adjust the spline handle. Or you can adjust the spline handle on one side but the smoother tangent constraint on the oath rose turns red but also cannot be re-created when you delete it.

I should ad that this advice was correct and creating a blend curve is the correct technique.

Please share the model so the Fusion 360 team has data to work with.

@ryan.bales @jeff_strater can you look at this please ?

In the last 3-4  weeks this kicked me in the teeth in a personal project, in a thread where I helped a user with a 2D spline (I reported that one), and I've seen this also when helping with the model in this thread just trying to create a simple 2D blend curve. 

So in essence this is not only limited to a 3D spline and the problem here is that I don't know a feasible workaround.

[Art5]

Well, that sucks. 

Thanks for your reply, I really appreciate it. 

Is there a workaround for this?

[Art5]

I've attached a file with the surfaces and problem sketch.

[TrippyLighting]

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@Art5 wrote:

Well, that sucks. 

Thanks for your reply, I really appreciate it. 

Is there a workaround for this?

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Are then two curves you are trying to create the spline between coplanar ?

Can you share the model ?

[TrippyLighting]

Where is the origin in the model ?

It is so far away from the geometry that when I try to create a new sketch I do not even get a plane to pick!

[Art5]

I've shared the surfaces in question. Negative on that, the edges are NOT co-planar.

[Art5]

I build in body position, the part file came from the customer.

[TrippyLighting]

So how far is the origin of the supplied geometry located form the part geometry  ?

[Art5]

I was able to build the spline by including 3D geometry first, then using those curves to build from. Unfortunately, when I try to build the patch, I can select the spline, OR the surface edges, but not the spline AND the surface edges. Why is this?

[Art5]

Looks like about 60 feet in X

[TrippyLighting]

So the object in the model you shared is approximately 6 " x 3" but 60 ft away from the origin so the ratio between object size and distance from the origin is 120! That is not a good ting and likely part of this problem with creating and selecting the curve.

Extrude a small surface from the curve and use edge of the surface instead of the curve. Then you can patch it.

I would usually not use a patch but a loft, but the curvature on some of the edges of this model is garbage and prevents a loft.

[Art5]

I tried extruding a surface from the curve and using that, to no avail. 

[TrippyLighting]

Not sure what to tell you.I succeeded in doing that just before I posted, but now cannot re-create it.

Things will possibly improve if you move the geometry closer to the origin.

[Art5]

There were 4 instances on this part where I tried to use this method. I was able to do it successfully on two of the instances, the other two I was not able to get it to work. I've attached a file with the required surfaces from the 2 failed instances. Hopefully someone can tell me what's going on with them and how to achieve what I need to do.

[Art5]

If the customer sends me more data pertaining to this job, that data will be in the body position they provided me with, therefore it's not conducive to my workflow to move the data out of it's body position. 

[etfrench]

Can't you move it, make the necessary changes, then move it back?

[TrippyLighting · Accepted solution]

After reading your intention to use patch where a loft is clearly the better alternative I went back trough some of your other threads.

I am not sure what experience you have in other CAD tools, but I believe part of your problems. stems from incomplete knowledge in using proper surfacing techniques, which disables you from properly identifying the source of these problems.  For your work, which I assume is some form of tools & die making there is one essential tool missing in Fusion 360 and that is an untrim tool.

In this case we can get away by the width of a hair not having to use it. But there are other cases where that will not work. Something you definitely should always do before lofting is check the curvature of the edges you are hoping to loft between. If the curvature is bad you'll run into trouble sooner or later.

[Art5]

I've used many different CAD systems, but mostly just in an educational context. At my last shop I used SolidWorks, but exclusively for 2D, never for 3D. At my current shop they originally had me using BobCAD, and as you described, I used the Untrim tool constantly. Despite being fairly powerful in the CAM aspect, I was unimpressed with the CAD aspect of BobCAD, especially coming from a background in CATIA and NX. This is why we decided to try F360.

I'm certainly no expert in this, I'm learning every day. Which is why I'm so grateful for these forums, that have been invaluable in helping me to use F360 successfully.

Your screencast was VERY helpful, I was able to use the techniques you demonstrated to finish this job, and on many others since. Thank you so much! 

[TrippyLighting]

No worries, we all learn every day! Glad it helped!