Component keeps reverting to an earlier shape when I start a sketch

[Anonymous]

Hi Folks,

I do like Fusion 360.  It seems to me to be a powerful and useful CAD program.  However, I sometimes get stuck in problems and can't figure out how to fix them or what is going on.  That is my current situation.

I have a certain component which seems to have the shape I want (or the body I am using which is part of the component seems to have that shape).  But when I start a sketch suddenly the shape of the component reverts to an earlier shape it used to have.  When I change the shape back to what it should be it just reverts again when I start the sketch.  What the heck is going on?  Any help would be appreciated.  I have included a Screencast video so you can see what I mean.  See here:  https://autode.sk/2JiDzpk

Thanks in advance,

Vincent

[paul.clauss · Accepted solution]

Hi @vincent1MFCMD

Thanks for posting! I think the confusion here is that, when a sketch is entered, Fusion rolls the timeline back to when that sketch was created. It must be that the part looked as it does when the sketch is entered when that sketch was created, and it was edited with operations to make it appear as it does later on in the timeline.

While I couldn't see where the sketch was located in the timeline, I am fairly certain that this is what's happening. If you right click the sketch and select "Find in Browser" and then roll the timeline back to that sketch, how does the component appear?

This gets into direct vs. parametric/timeline based modeling, which I've mentioned briefly in the screencast. The resources below may help you understand the expected direct and parametric behaviors in Fusion:

• Fusion 360 - Direct Modeling vs. Parametric Modeling
• About direct and parametric modeling
• Direct vs History based modeling (forum thread - this is an interesting discussion)

I've shown a simple example of this in the screencast below. I hope this helps!

[Anonymous]

Hi Paul,

Thank you for your detailed response to my question.  I regret that it has taken me so long to reply to your response.  My life is filled with complications and difficulties and I can only work on my CAD project part time.

I have reviewed your response and the videos you included and also I read the first three pages of the discussion about direct modeling vs. history based modeling which you provided a link to.  (Yes, that discussion is interesting.  Based on what I read and the nature of my project I think I should be working in direct modeling mode and probably will be doing so in the future.)

In your response you stated that you thought the problem I was having was that the sketch was located in the timeline in a place where the shaft part had the wider top portion and that that is why whenever I tried to edit the sketch the shaft reverted back to that other shape with the wider portion on top.  I think you were right.  But then the question arose: “How do I fix this?”

I decided to make a copy of the sketch, thinking that a new copy would be located later in the timeline and thus it would not have the problem of the older sketch.  But I had difficulty in finding a way to copy the sketch.  Finally I saw that I could create a new sketch right on top of the old sketch and then use the “Project/Include” command to bring the parts of the prior sketch that I needed into the new one and that seemed to work.  The new sketch did not have the problem of the old sketch.  So in that way I was able to solve the problem.   (Of course I could have created a new sketch from scratch but I wanted to find a better way to solve the problem than that.)

(I also tried to locate the original sketch in the timeline because I thought I had read that one can drag items in a timeline to other places in that timeline.  But when I tried to drag the sketch in question in the timeline it would not move anywhere.  [My computer only has 4 Gigabytes of RAM.  Perhaps that is causing a problem.]  Should I be able to drag the sketch to move it in the timeline?)

Anyway, the bottom line here is that your answer was correct and based on it I was able to solve the problem.  Thanks for your help.

Best regards,

Vincent

[paul.clauss]

Hi @vincent1MFCMD

Thanks for the response - I'm glad I was able to answer your question! 

You need to be in the sketch to copy sketch geometry. While you can't copy a sketch, you can copy sketch geometry into a new sketch. I've shown this in the screencast below with a very simple example.

The ability to move sketches in the timeline depends on the plane the sketch was created on and the features that are dependent on the sketch - ordering matters when working with the design timeline. I've also shown a very brief example of this below.

I hope this helps explain these concepts! Feel free to reach out if you have any questions.

[Anonymous]

Hi Paul,

Thanks for your screencast and response.  That explains and clarifies why one can sometimes move an item in the timeline and sometimes one cannot do so.  Regarding how to copy a sketch, I had finally figured out how to do that (using the “Project/Include” command) but you have provided an alternative way of doing it (using the copy and paste commands).

Thanks for your help.

Best regards,

Vincent