relative position of components and sketch changes inside sketch - Help!!!

[thepirate1]

Hello Community: 

I made a "cylinder align sketch" which gives the axis for the cylinder.  I made the cylinder and it's axis is along this line, starting at the endpoint.  So far so good. 

Then I made a new "mounts sketch" in the same plane as the first, and made some sketch objects that would be extruded to make mounts for the cylinder.  Stuff happened, things went out of align.  I tried to fix stuff.  Later, I went back into the mounts sketch, and it was clear that the object in the mounts sketch are in a different position in the sketch than when out of the sketch.  Recompute all does not help.  It's all shown in the attached screencast.  The sketch is in the same plane as the cylinder align sketch, so the appearance of relative position change cannot be an artifact of the view.  

Help!  I have spent many hours trying to save this drawing/model.  What's going wrong and how do I fix it? 

-An extremely frustrated TCP. 

[Oceanconcepts]

There doesn't seem to be a screencast attached, and it's hard to comment without seeing more of what you describe, either screencast, screen shots or even better a file.

[thepirate1]

Sorry!!!  Here is the screencast. 

-TPC

[Oceanconcepts]

I think what is happening is that when you edit the sketch, you are jumping back to a previous point in the timeline where the cylinder was in another position. When you exit, you go back to the end of the timeline. The timeline remembers positions. You can drag operations to different points in the timeline to alter this relationship. Or you could simply roll back the timeline marker to the point of you creating the mount sketch (assuming all was right at that point). You then have the option of rearranging events, deleting some, or deleting everything after the marker.

I’m not completely sure I understand your intent, but if you need to to move the mounts sketch you don’t necessarily want to edit it, you can just right click and Move- if nothing has been created that is dependent on it. 

I’d probably approach this by setting up a construction plane and then sketch perpendicular to the cylinder axis you desire, project the axis to a point, then make the cylinder on that sketch to the correct diameter. Then make your mounts sketch as you have done, bisecting the cylinder. Project the cylinder axis to the sketch and constrain the mounts axis to be coincident to that axis- I’m assuming you want the mount pins to be centered on the cylinder. That would constrain them, and even if you later go back and change the cylinder or mount diameter they will keep the relative position. 

I will also say that while your parts are properly set up as components, your sketches are all in the root component. Your life with Fusion will be much happier if you create and activate components before creating the sketches on which they are based. This will keep the sketches organized within the components to which they pertain. 

I can’t do it tonight, but if this isn’t clear (or I have it wrong) and you can give a fuller picture of your design, I could make a screencast to show what I’m suggesting. 

[thepirate1]

Thank you very much Ron for your comments.  Unfortunately, that is not the problem. 

I just re-opened the design.  I made sure I was at the end of the timeline.  Next, I opened the sketch, and checked the timeline.  Same thing as in the screencast.  

Is it possible the file is corrupted?  Or just a bug? Is there some way to recover from this? Anything else I can do? 

You asked for a "fuller" picture of the design.  Is there some way I can send it to you privately? 

Thanks, 

-Bruce

[Oceanconcepts]

I've sent you an email in response to your PM about looking at the file.  

When in the timeline was your sketch created? What do you see if you roll the marker back to that point? 

[Oceanconcepts · Accepted solution]

After looking at an earlier version of your design, I can confirm that what is happening is that when you edit the sketch, you are jumping back to a previous point in the timeline where the cylinder was in another position. When you exit the sketch, you jump back to the end of the timeline. At the point you created the sketch, the cylinder was not in the desired alignment, and whenever you edit the sketch you take the design back to that point, ghosting out the rest of the subsequent timeline- as any parts dependent on the edited sketch would update when you exit. You can see this in the screencast when I roll the marker back. There are a lot of Move operations in your timeline, several of which appear to probably be inadvertent, this kind of thing is a hazard. 

Two ways to avoid this would be to 

1) work in direct modeling, without a timeline or parametric constraints. This can be good if you don’t quite know where the design is headed, and need to move things around a lot. I doubt this is your situation, as you seem to have a clear design intent. 

2) Build your design around parametric sketches, rather than primitives. Create your sketches with the relationships you want to hold defined, then use modeling tools to create parts from the sketches. 

For sketching and setting up parametric relationships:

http://fusion360.autodesk.com/learning/learning.html?guid=GUID-CD071296-EA6C-4DD7-B6AC-1DE52D4D310E

There is a good class from Autodesk University available online that covers model management:

http://au.autodesk.com/au-online/classes-on-demand/class-catalog/2015/fusion-360/cp10167#chapter=0 

[thepirate1 · Accepted solution]

Long post meant to summarize and give benefit to community:

Summary of my Lessons Learned ------------------

* Deleting sketch profiles is very bad.  You can delete relationships you forgot about, leaving Fusion confused about where various components go. (Note A) 

* Aligning to  bodies/components/rectantular profiles/etc. 2-d or 3-D centers requires laborious manual definition of centers.  Define them and live with it, you will be much better off. (Note B)

* Sketches with dimensions and relationships specified by user-defined parameters are good.  They allow you to change things without having to update anything, without causing problems.

* More sketches are better, i.e. anything not directly dependent should be on a separate sketch, even if each sketch is in the same plane.  (note C) 

* The time-ordering of operations is important and subtle in fusion. Including in sketches. Pay attention to this. (Note D)

-------------------------------

Note A: In my example file, delete_sketchitem_demo, I created a sketch, extruded a few profiles. Then I made a box starting with the selection of one of the extruded thingies. Next, I deleted the extruded thingy. Nothing happened. Next, I deleted the profile in the sketch. THAT's when I got the warning and things went bad. You can see why: If the box I made has a data value that says, “look at the z value of the top of the profile A in sketch 1", and then I delete that profile, well, this will cause problems. This is probably the problem I was having with the cylinder align profile, the subject of this thread. I went back to fix things, but fixing them by deleting a sketch or profile is a DISASTER. Anyway, don't delete things in sketches. It's not so good that fusion isn't smart enough to fix this on it's own (using the world coordinates for the time being), or that it would not at least ask you to choose between an object's world coordinate or click on some other reference, at the time of your delete, but anyway I think I know how to prevent the problem. 

(I could not get "moves" to create any problems, despite worries about that from Oceanconcepts.)

Note B: Construction>Point at Center of Circle/Sphere/Torus doesn't work for a cylinder (puts center on a face, not a volume).  I had to sketch a line across the cylinder axis, and then align using the sketch midpoint tool).  To make a midpoint of a rectangle (copying from a post), you have to draw a diagonal, select line, right click on construction/normal, and then use sketch midpoint constraint to align. 

Note C: More Sketches make selection easier.  They make deletions not a catastrophe (see below). Note that sketches in the same plane can have different orientations; putting a sketch in the orientation you need can make life *much* easier; e.g. pulling a line straight down is only easy if "down" is oriented correctly on the sketch.  I took oceanconcept's suggestions on this and everything worked much better. 

Note 😧 First, general observation: I want a shaft to go through some kind of body, off center.  I'm lazy, I made my shaft one continuous cylinder through the body.  The shaft radius was greater than the distance to the edge, so it protruded out of the surface of the body - ugly.  To fix this, I made the body invisible, then used a box as a cutting tool to shave off the exterior part of the shaft.  Then I turned back on the body.  All worked great.  Had I not turned the body invisible during the cut, it would have left a groove cut into the body.  See what I mean how time and the order of operations is critical? 

Now, Oceanconcepts has observed that what was happening when my components were jumping around in orientation was that inside the sketch it was referencing the appearance of non-sketch parts at a PREVIOUS time.  Now, before I went into the sketch, I made sure I was at the end of the timeline.  Now, INSIDE the sketch, there was no visible change in the timeline, I was still at the end of the timeline.  Yet, the sketch showed an earlier epoch. That is, apparently a snapshot of external items at the time of the first save of the sketch is "frozen in" forever.  Or maybe, the orientation of the sketch is frozen? Not sure. It's not that the timeline jumps back, it doesn't.  I checked.  It's that the sketch has either relative positions or actually a time snap-shot of the design in it.  So, again, BAD IDEA to delete or even change a sketch without deleting or changing everything that uses it as a reference, or uses something in the sketch as a reference. 

-TPC

[Oceanconcepts]

Good observations. A few comments re. your notes:

Note A:  In general, deleting in the drawing in a timeline design is a bad idea (there are exceptions, but it’s important to understand why this can cause problems). Rather, go back the the point in the timeline, and delete the original operation. If you make a sketch, extrude something, then delete that extruded part, all of those will be recorded as events in the timeline. If instead you go to the timeline and delete (or suppress, another option) the original extrude operation, you will be back to ground zero with your sketch. Deleting a sketch, or any operation in the timeline which has downstream dependencies will create errors. It’s important in history based modeling to keep a logical structure in the timeline, part of the reason why activating components is so important. Fusion warns you of those errors when they occur, and highlands with red markers problematic issues in the timeline. It’s best to fix those right away when the warning comes. This isn’t unique to Fusion, it’s a fact of life with any parametric modeling program.  Note that you can also drag operations to different positions in the timeline, sometimes that can fix conflicts. 

But Fusion also (unlike most other programs) has a direct (“do not capture design history”) modeling mode, where you can create parts, move, add, subtract, move sketches around, and pretty much do anything, and since there is no history or timeline you can’t get into trouble for what you do. I work in direct modeling a lot, particularly when I’m developing concepts. It’s an easier space to noodle around in. Both modes have strengths and limitations, but in may ways direct is an easier place to learn 3D basics. 

Note B: If you are talking about a solid cylinder, placing an axis will give you a line through the center, but if you want the actual center of the entire solid, then yes, that would require another step. If the ends of the cylinder are co-planar, you could use the combination of an axis and a mid plane to position a sketch and sketch point. But it seems that a tool to find the mid point of a solid would be a good thing to have. 

Note C:  Yep, more sketches and referencing other sketches, helps maintain logical order. 

Note 😧 Order of operations can be important, but what you describe here is a basic Fusion convention that operations like cut are dependent on body visibility. You will cut through everything that is visible, and nothing that has visibility turned off. This is distinct from operations like split body or combine, where you define the bodies that are involved. You can also use faces as splitting tools with the split body command. 

re. components jumping around:

I’m wondering if it would be better from a UI standpoint to have the marker move back to the point in the timeline where a user is editing something, just to make the relationships obvious. The rest of the timeline is still there, and will remain unless you explicitly delete it, but the only things that will ultimately change are things dependent on the aspect of the design (sketch, for instance) you are editing. As soon as you exit the sketch, Fusion tries to update the downstream operations that are dependent, and takes you back to the end. Yes, you are correct, when you go back to edit something, you are going back to a frozen snapshot of the design at that time, and have the ability to alter all downstream dependencies with your edits.  That is the power and the peril of the timeline. 

There is a timeline intro here:  http://fusion360.autodesk.com/learning/learning.html?guid=GUID-FA6C0CA9-DCEA-4ADD-B993-6594FE28457A

[TrippyLighting]

I have to admit that I have really not paid attention to what the timeline deisplays when I edit a sketch, however if it is not actually visually jumping back when editing a sketch it woud make a great addition for the Idea Satation and would have my immediate vote.

The timeline concept does not exist in any other CAD software I am aware off and so it is new to expariences and new users alike. It is very easy to see how that is confusion to a user if it cannot be percieved throug an indication in hte timeline. This has been the cause for many threads when other users stumbled aross the same issue.

[Oceanconcepts]

Any time you edit something in the timeline, the marker stays at the end, but everything in between grays out. I hadn’t thought about it before this thread, but that could be confusing to those unfamiliar with the concepts of history / parametric modeling, or who are just new to the timeline interface. I think moving the marker as well would be a better visual cue. I’ll put this in the Idea Station. 

Fusion’s timeline interface is a much better interface for understanding history in the model than others that I have seen. I’ve seen it presented as an expandable list, like a file structure, but the timeline is much more useful.