Why won't it split this body?

[RogerInHawaii]

I'm trying to split a body in half and it keeps indicating that it can't do it. It let's me choose the body and then a plane as the splitting tool, just like I've done successfully a thousand times before with the Split tool, but it just won't do it.

I've attached the design in case anyone cares to give it a try and maybe figure out what's wrong, why it won't do it.

It let me split a different body (named "Tool Work Area") within this design file just fine. What could possibly be different about this one?

Or have I just gone totally bonkers?

[jhackney1972 · Accepted solution]

The attached video will show how to solve your issue.  Model is attached.

[TrippyLighting]

I am going through the timeline to find the root cause to actually answer the question, but came across this operation.

I am not sure I understand its intention. Could you elaborate ?

Is this a geometry "clean up" attempt ?

There is a more accurate way to create the loft if you're interested. The input curves for the loft all have clean curvature, but the edge the combine operation creates is pretty bad even with the bare eye.

[TrippyLighting]

The problem is the three-point construction plane.

If you use the ZY origin plane for splitting the operation works fine. 

[TrippyLighting]

A better loft:

 Model is attached.

Your models have reached a level of sophistication, where you would benefit from learning some good surfacing techniques. You know where to find us 😉

[RogerInHawaii]

I attempted to use the 3-point plane because the ZY construction plane failed. I selected the body, selected the ZY construction plane, it showed the red circular splitting object in the middle of the Body, but reported an error that the plane did not intersect the body, even though it clearly WAS showing it as intersecting the body.

It was only after that weird failure that I tried creating a plane right AT the body, using points ON the body that would absolutely intersect the body. And THAT attempt to split also failed.

[RogerInHawaii]

Yes, the loft isn't quite as clean as I'd like it to be, leaving a bit of a bump near the edges. And yes I was attempting to clean that up.

I tried making the upper input curve, the "end" curve in the loft operation, exactly at the top edge of the side input curve, the "starting" curve, but the loft operation didn't like that, apparently not liking one line of one curve being coincident with a line on the other curve. So I moved the upper input curve ever so slightly above the other curve, like .001 inch above. And THAT's what resulted in that slight bump and why I attempted to clean it up.

I don't see how that might have interfered with doing the subsequent body split.

[RogerInHawaii]

Thank you, TrippyLightning, I think I followed along in the design file you uploaded. The difference seems to be that the start and end loft curves don't have the horizontal line across the top of the body, and you arrived at that top curve by a little trick of cutting the face to produce it. The loft operation then succeeded where it hadn't by using the curves I had created.

[TrippyLighting]

---

@RogerInHawaii wrote:

...
I don't see how that might have interfered with doing the subsequent body split.

---

It didn't, but it deserved some attention. These particular modeling "accidents" or workarounds very often cause further modeling problems later in a project. Then attempts to repair them meddles with subsequent features in the timeline  etc.

Some tools in Fusion 360 are very sensitive to curvature problems. The shell tool for example is one of those.

Better to address such issues properly.

[TrippyLighting]

---

@RogerInHawaii wrote:

... and you arrived at that top curve by a little trick of cutting the face to produce it....

---

I almost always prefer to work with edges rather than projected curves. The reason is that a splines or curved edges  projected onto a curved surface almost always have curvature problems, whereas a split created with the same inputs  edge is clean!

When working with lofts, the curvature comb (to check input curves and resulting edges) and ISO curve analysis (to check the lofted surface) are indispensable tools.

[RogerInHawaii]

Thank you for looking in to this problem.

I'm following along on the video that you created.

At the very beginning you click on a Combine operation, which by the way does NOT appear Red in the timeline, and select to Edit the Feature. When you do that it comes up and shows an error, saying "Loop containment cannot be determined".

Well, I followed along in my design and selecting to Edit that Combine operation does NOT show any error. It appears to do it just fine.

You then say that in order to fix the problem with the error I need to right-click on the suppressed sketch that's just a few operations to the left of the Combine operation in the timeline and UN-suppress it.

Right off the bat, this seems really odd. If an operation is suppressed then it means it isn't processed by Fusion, so how it can in any way contribute to subsequent problems with Fusion is, well, just weird to me.

BUT I followed along and Un-suppressed it.

That sketch, by the way, simply contains some circles and a projection of the oval end that had been created in a prior operation. That sketch is ONLY for showing my colleague, who I am doing this job for, to let him see the oval shape relative to the existing round shape. It is NOT used in any subsequent operation in the design. I had suppressed it because it had some invalid projections in it, as a result of trying various operations to fix the split-failure issue. Since the sketch is ONLY used for showing my colleague the round/oval comparison, it really wasn't necessary to bother fixing the sketch.

BUT, again, I followed along and re-defined the sketch plane as you suggested.

I then did the Compute All as you suggested and YES, I was then able to split the body!!!

However, I then backed up and UN-did all the operations you suggested, (un-did the redefine sketch plane, undid the UN-suppress of the Sketch, so that it was back to being suppressed).

And all I did then was the Compute All, and with just doing that I was able to do the split body OK.

So it appears that all it needed was a Compute All to clear things up and allow the Split to work. What it was clearing up? I have no clue.

I do indeed THANK YOU for taking the time to go through my design and ending up finding a solution, which in the end was just a Compute All.