As-build-joint problem for assemblies - bug?

[Anonymous]

I've noticed some bug or at least unexpected behavior when using as-build-joints.

The situation I quite often have is, that I have multiple "assembly"-components (each with a sub-structure of components linked by various joints) which I then want to join together on the "root" level by joints as well. It works fine with "regular" joints or with "as-build-joints" when I select things in the model-view, however, I naturally often selecting things in the browser-list and then it does not work.

The typical work-flow:

- Click "as-build-joint"

- Click two components (on root level) in the browser

- Select joint type (i.e. rigid)

- DONE.

If you do it like this (see the screen-cast), a "joint" is properly created on the root-level, but it is "empty", i.e. it does not link anything. As a result, the sub-components can still move freely around.

This has confused me a lot for a very long time until I realized that I have to either use "regular joints" or select the "as-build-joint"-components by clicking in the view, but not in the browser.

[jeff_strater · Accepted solution]

Hi @Anonymous,

This is a good question, and important to understand how Fusion works.  Actually, the behavior that you describe (I'm pretty sure - I would need to see your design to be absolutely certain) is the correct behavior.  It all has to do with how components (especially sub-assembly type components) behave in Fusion.

The short version is:  When you select the top of the sub-assembly as a component in an as-built joint, you are only constraining the top level of that sub-assembly, not the child components of that sub-assembly.  Fusion sub-assemblies are all "flexible".  Meaning that the child components can move independently of the sub-assembly itself.  See the screencast below for more details:

(I apologize, because it is kind of long.  Audio is included):

Hope this helps,

Jeff

[Anonymous]

@jeff_strater

Hi Jeff,

Thanks a lot for the extensive video (and the hint of switching the origin display on!).

I think I do understand what's going on under the hood now. However, there are still two points open for me:

1) I'm still confused why it should be "correct" that when I have joined a component (C1) to the "origin" of an assembly-component (AC1), moving C1 and hence moving the rigidly linked origin AC1 should change the relation between the "children-components" (AC1_C1, AC1_C2) of the AC1 and the origin of AC1. For me, these relations should stay "constant" in this case. The relation between AC1 and AC1_Cx should only change when I move AC1_Cx - because then I am moving a child within the assembly-coordinates system.

To me, this is the "same" scenario as if I right-click AC1 and "move" it using "move components". Then The origin of AC1 moves - and the children move with it. I would expect the same to happen when I move a "rigidly joint" component. That's why I put "bug?" in the title.

I've added another Screencast at the bottom to show what I mean. At the end of the video, when I move the component with the "move", I would expect that both would do the same thing:

- Moving the linked component.

- Moving the origin of the assembly-component.

Both should - in my opinion - move the assemblies child-components. But only one of them does.

2) Ignoring the above and taking it as a fact: Can I "anchor" any sub-component (rigidly join) to its assembly-parent component? (I can "ground" it to the world. But I only want to keep it "fixed" with respect to the AC's origin.

If I understand things correctly, that would be the "missing link" and if such a fixation would exist, joining the assemblies would do the 'expected' thing as well.

[Anonymous]

Sorry, forgot the screencast. (And can't add it by "editing" my post ? )

[jeff_strater]

Yes, it is a bit inconsistent that Move does something different.  To be honest, I had to try that one myself to see how it behaved.  But, you are correct:  Move of a sub-assembly will move the whole thing.

Regarding this question:  "Can I "anchor" any sub-component (rigidly join) to its assembly-parent component? (I can "ground" it to the world. But I only want to keep it "fixed" with respect to the AC's origin.", the answer is yes.  The easiest way to do this is to create an as-built joint between the child components and the origin of the sub-assembly:

Jeff

[neljoshua]

@Anonymous,

I have been following along.  @jeff_strater does a great job of explaining things; there is often something I can learn.  As-built joints sometimes seem dodgy for me, as well.

I often do work with linked/imported sub-assemblies.  For each sub-assembly that I start, I ground one component and then join all of the others to it using standard (i.e., not as-built) joints.  I have almost entirely stopped using as-built joints due to the aforementioned dodginess.

[Anonymous]

> @jeff.strater: "Move of a sub-assembly will move the whole thing."

I just think, that is what should happen with the in-build joints on assembly-components as well. No inconsistency. No "oddness" for newbies. One can still "move" sub-components unless they are "tied down" to the assembly-origin. (The last one might still confuse newbies, but that would be where your explaination comes in.)

@neljoshua: Exactly the situation I ran into this issue. However, "as build-joints" are generally a great feature, in particular when parts where exported separtely with "correct" world-coordinate placement but no obvious "joint" (i.e. no shared face, edge etc.).  I think being able to use them "comfortably" on loaded in assemblies would be a great plus.