Understanding Component positions and projections (without joints)

[jandyman]

I apologize for what is probably a basic question. I don't even know how to ask it right because I sort of thought I understood what has happening until I got unexpected results. I had read a number of related posts, learned a lot, but I guess not enough. I think the best way to ask the question is to describe what I did, ask how to fix it, and why it didn't work as I expected, because I clearly don't understand component positioning properly.

In my case I'm building a master component/assembly "around" a sub-assembly. I built the sub-assembly without incident, including joints. Then I worked on creating the containing component/assembly. In this case the containing component is basically a set of cavities within a body which houses the sub-assembly. When I created the containing assembly/component, I did *not* create any joints, because in the containing assembly there was nothing to attach anything to, since I hadn't built anything yet. So I built this new assembly/component without repositioning the contained sub-assembly, got really far along. I used projections from the sub-assembly in sketches to create the cavity.

Towards the end, I realized that the sub-assembly needed to be repositioned in Z relative to the master component/assembly, so I moved it. But the projections I created in the sketches in the containing component/assembly did not move. In fact, the understanding that the sketches had of the position of the sub-assembly were clearly different than where I had moved the sub-assembly.

In the attached design, the containing component/assembly is "Master Assembly:1". The sketch "Rear Axle Groove" used projections from the "Arm SubAssembly:3", but now that I moved "Arm Subassembly:3", the projections did not move to match the move of the sub-assembly, so the sketch is no longer correct.

Clearly I don't understand something basic. What's wrong with my workflow? How can I create components/assemblies based on other components using joints, when those joints can't exist yet because the containing component/assembly hasn't been created yet. And if joints are the wrong approach, what is the right approach?

I hope this is not too confusing, and I'm grateful for any help!

[davebYYPCU]

I don’t have access to your file atm.

When you find that the article had to move.  (Usually done by editing the current position)

Roll the timeline back before the sketches that rely on it.

Edit the file at this time of the timeline, and let Fusion do the updates to the sketches.

Might help….

[laughingcreek]

seems like your having chicken and egg type problems. (it's the egg btw).

a few thoughts-

a design of this nature should not have ANY position captures in the time line.  don't know if this is a source of your troubles, but it's a good idea to operate with out them.  components are positioned relative to each other in 2 ways.  by building them "in place" followed by an as-built joint, or by using a regular type joint.

having bodies at the same level as other assemblies or components in the hierarchy can get real mind bendy when it comes to positioning with joints.  fusion allows it, but generally not a good idea-

I haven't been able to examine your model closely, but sounds like your having timeline related difficulties.  

sketches that appear in the timeline BEFORE a component repositioning (with a joint) won't reflect  the new position.  sketches that appear in the timeline AFTER the repositioning (with a joint) will.

and yes your question is confusing and I'm not sure I'm following your issue.  You might need to break down the problem more clearly.  (or start with the egg instead of the chicken)

[jeff_strater]

I, also, have not yet had a chance to look at your design.  But, this paragraph may hold the key:

"Towards the end, I realized that the sub-assembly needed to be repositioned in Z relative to the master component/assembly, so I moved it. But the projections I created in the sketches in the containing component/assembly did not move. In fact, the understanding that the sketches had of the position of the sub-assembly were clearly different than where I had moved the sub-assembly."

Remember - Fusion is timeline-based.  The compute happens in timeline order.  So if you move something (there is a different topic about moving bodies vs components), you need to make sure that that move (and a Capture Position, if you are moving components) happens before (in the timeline) the sketch projection in question.

[jandyman]

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@jeff_strater wrote:

I, also, have not yet had a chance to look at your design.  But, this paragraph may hold the key:

"Towards the end, I realized that the sub-assembly needed to be repositioned in Z relative to the master component/assembly, so I moved it. But the projections I created in the sketches in the containing component/assembly did not move. In fact, the understanding that the sketches had of the position of the sub-assembly were clearly different than where I had moved the sub-assembly."

Remember - Fusion is timeline-based.  The compute happens in timeline order.  So if you move something (there is a different topic about moving bodies vs components), you need to make sure that that move (and a Capture Position, if you are moving components) happens before (in the timeline) the sketch projection in question.

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Of course, how silly of me. Forgetting the timeline issue because of my newness to components and assemblies. But now I have another timeline related issue. The move that I put in the wrong place in the timeline does not appear in the timeline. In order to get everything back in sync, I want to first undo that move, then go back in the timeline and add the move at an earlier time. But I can't undo the move because the move operation doesn't appear in timeline. Why is this and what do I do?

@jeff_strater @laughingcreek @davebYYPCU 

[laughingcreek]

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@jandyman wrote:...The move that I put in the wrong place in the timeline does not appear in the timeline. ...

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move (and align) does not create a time line feature for components. (it does for bodies and faces).  for all intents and purposes using move or align on a component is just an accurate way for dragging the component with the mouse.  it's a temporary positioning.  after moving a component you can use a position capture, but that's generally not a good way of doing it.  better to position with a joint.

[jeff_strater]

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@laughingcreek wrote:

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@jandyman wrote:...The move that I put in the wrong place in the timeline does not appear in the timeline. ...

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move (and align) does not create a time line feature for components. (it does for bodies and faces).  for all intents and purposes using move or align on a component is just an accurate way for dragging the component with the mouse.  it's a temporary positioning.  after moving a component you can use a position capture, but that's generally not a good way of doing it.  better to position with a joint.

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I'd like to put a little context on @laughingcreek's comment here.  If you are truly doing position-based modeling (where features are dependent on the position of a component), then you should use Capture Position for that purpose.  That is, in fact, why Capture Position is in there.  Ideally, though, @laughingcreek is correct - that position change should be driven by a Joint position (say, from Drive Joint).  Below is a simple example of position-based modeling from a class I did a couple of years ago.  The idea here is to produce a cut in the body based on the position of the handle.  The 2 features to the right of the timeline illustrate (step forward to see them in action)

Model is attached for reference.

[jandyman]

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move (and align) does not create a time line feature for components. (it does for bodies and faces).  for all intents and purposes using move or align on a component is just an accurate way for dragging the component with the mouse.  it's a temporary positioning.  after moving a component you can use a position capture, but that's generally not a good way of doing it.  better to position with a joint.

But then we get back to a point I made in my original post. At the point in time that I bring the sub-assembly into the master assembly/component, I can't create a joint because there is nothing to attach to. This is because I'm creating the body that the sub-assembly would attach to based on the shape of the sub assembly. What is the correct workflow in this case?

Also, getting back to the temporary nature of the component move. If I now ignore that the sub-assembly is in the "wrong" position because I moved at at the wrong place in the timeline, and I now go back and put the move in the correct place in the timeline, will that later temporary move still be there, putting it in the wrong position again, or will it disappear? Just trying to understand how all this interacts. 

I did a quick read on capture position and it doesn't sound like it is recommended for this scenario. So do I build my master assembly around the sub-assembly just enough to guarantee proper position, then do an "as built joint" to lock it in and continue refining the master assembly/component? And if I need to change it later, I go back to that place in the time line, delete the as built joint, move the sub-assembly to the correct location, then create another "as built joint"?

I hope all these questions make sense.

@jeff_strater 

[jeff_strater · Accepted solution]

"But then we get back to a point I made in my original post. At the point in time that I bring the sub-assembly into the master assembly/component, I can't create a joint because there is nothing to attach to. This is because I'm creating the body that the sub-assembly would attach to based on the shape of the sub assembly. What is the correct workflow in this case?"

Again, with the caveat that I have not yet had time to look at your design, I think I understand your question.  Even if there are no bodies or components in the top-level design to attach to, you can, in fact, still create a joint to your sub-assembly.  Even an empty design has a Origin, and you can attach a joint to the Origin.  But, I think the bigger point, here is:  You do not have to create a joint immediately upon inserting your sub-assembly.  It would be fine to create a body in the top-level assembly, then create a joint between it and your sub-assembly

"Also, getting back to the temporary nature of the component move. If I now ignore that the sub-assembly is in the "wrong" position because I moved at at the wrong place in the timeline, and I now go back and put the move in the correct place in the timeline, will that later temporary move still be there, putting it in the wrong position again, or will it disappear? Just trying to understand how all this interacts. "

If there is no Capture Position for the "wrong" move, later in the design, then that move should just disappear.  If it does not, for some reason, you can just click on "Revert Position in the UI":

"I did a quick read on capture position and it doesn't sound like it is recommended for this scenario. So do I build my master assembly around the sub-assembly just enough to guarantee proper position, then do an "as built joint" to lock it in and continue refining the master assembly/component? And if I need to change it later, I go back to that place in the time line, delete the as built joint, move the sub-assembly to the correct location, then create another "as built joint"?"

Again, as I said above, I disagree.  Capture Position is intended for this exact workflow.

"I hope all these questions make sense."

Yes, and thank you.

[jandyman]

Thanks to everyone here. I understand everything a lot better now!