3D sketch is incredibly buggy and dumb

[Mulakulu]

What can I do to prevent Fusion from being incredibly dumb when it comes to using constraints and dimensions in 3D sketch? I get that it's a complicated thing for a program to move things around like this in 3D space and calculate where all the points even can be, but when we're talking about a line that's fixed in place and one like that's free to move wherever it wants, and trying to restrict the angle makes the damned program break, then there's clearly something wrong. This isn't the only dumb thing Fusion does. I can have two lines on a plane and try to combine the tips with the Coincident constraint and it just goes "Nah. That's not possible" when I can literally drag the points together manually..

(You can probably tell from my language that I'm incredibly frustrated after working for 3+ hours with repeated dumb error message after dumb and just flat out wrong error message)

I know I could have just made this simple design using extrusions, 2D sketches and other solutions, but I wanted to do it all in one go. So, is there a better way of treating 3D sketch, what are the limitations, some bad and good habits and so on?

[davebYYPCU · Accepted solution]

I know I could have just made this simple design using extrusions, 2D sketches and other solutions,

Design Differently is a marketing slogan, not an instruction.

but I wanted to do it all in one go. So, is there a better way of treating 3D sketch

Nope.  Excellent demo of the reason we don’t use them.  (Dimensions and constraints are unreliable.)

Might help…

[Mulakulu]

Dang. It's clear it doesn't have to be that way though, ideally. Like you said, excellent demo that fusion's algorithm isn't perfect, although I have no idea what the perfect algorithm would be.

Followup question though. If dimensions and constraints are unreliable, what other options are there? What is the most reliable way to model such that if you change parameters that were set early in the history, you'd rather consistently get the expected model out the end? I hope you have a more reliable solution and that when you said unreliable you meant compared to something else.

[davebYYPCU]

If changing parameters with blue articles, you are in for the next nightmare.

Fully constrained 2d sketches and modelling tools using those sketches, works for me.

Might help…..

[TrippyLighting]

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@davebYYPCU wrote:

...

Fully constrained 2d sketches and modelling tools using those sketches, works for me.

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Have worked for me as well for the last 25 years with parametric 3D CAD.

3D sketches have their purpose for some surface designs and perhaps frame and piping design.

[Mulakulu]

"Blue articles"? Like, undefined lines and such? If so, yeah, that totally makes sense, since it seems Fusion is pretty selective with what it grants "black", but I guess a line is blue and locked in place because there could be another valid spot for it to be, just not somewhere you can drag it, and "black" means fusion knows for sure where it's supposed to be. Is this what you meant?

[davebYYPCU]

Black denotes fully constrained, a red pin on the sketch label denotes all sketch articles in it are effectively black (purple or green).

Blue, Orange lines and White points - Fusion sees as still able to move from here.  Add Change parameters involving undefined articles that have no anchor to work from - generates the nightmare.

I guess a line is blue and locked in place…. - is not possible.

Might help….

[Mulakulu]

I've had blue lines that are "locked in place" as in I can't drag them around, and the constraints logically show that moving them should be impossible, but I'm guessing they were in a bi-stable state, where it had multiple possible immovable and stable places, which isn't "locked" locket. Just a finite amount of stuck locations rather than an "infinite" gradient letting me drag them. Anyway, thank you both so much for your help. I appreciate it tons

[hansvaneven]

I for one really like to use 3d sketches in some cases and no matter some people claim you can do it otherwise it's there and should work better. it's actually a great tool when it works. The problem is that some days you can work without a single issue and then the other day you open up your sketch and design and you have nothing but bugs and errors (like today) not sure if this is related to updates, I guess so, but the whole 3d sketch thing could really use an update.

[TheCADWhisperer]

@hansvaneven 

Can you attach an example?

[hansvaneven]

I'd have to make a new one as this particular project is for a client, so I can't share, but to put it easy 3d sketching has always been buggy for me, I managed to work around some issues but it would be great this part could be updated. 

[hansvaneven]

I can say for sure there's something seriously broken in 3d sketching, it's hard to demo as this is a client's project so i'll need to do a specific demo file, but even with an old project that worked for me, I just can't seem to coincident some points to a line in 3d sketches and also very hard to move handles in 3D sketches, this worked before so it must be something related to an update ? 

[TrippyLighting]

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@hansvaneven wrote:

I can say for sure there's something seriously broken in 3d sketching, ...

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The 3D sketch functionality has never been fully developed and has many open issues.

That is one of the main reasons why we usually recommend only using it for "special occasions".

[jeff_strater]

It would be helpful if you could document the issues that you are encountering.  A Coincident between a point and a line should work, and as far as I am aware, there have been no changes that would have prevented this from working.  Moving handles in 3D sketch has always required the use of the Move tool - nothing has changed there, either.  If you encounter specific problems, please supply a model and a video showing what does not work.  Without that, it just just vague complaints, with no hope of ever being fixed.  We cannot fix what we can't see ourselves.

[hansvaneven]

Yes I perfectly understand and this is why I only use it on small areas. I managed to work around the issues and have had good luck with it on this particular use for a project but the reason that coïncident points to splines doesn't work anymore while it perfectly worked before shows there's an important issue since the last update. I really hope Autodesk listens here and can update the 3D sketching as it's pretty useful for me and from testing easier to work with in this particular area vs 2d sketches but that's my work on it, I can use both but prefer 3d sketching in some cases. 

[hansvaneven]

Hello Jeff, thanks for your reply, though I must say I found the "vague complaints" remark a bit dismissive. I work full-time on professional client projects and unfortunately cannot share the actual files due to confidentiality constraints, something I hope you can appreciate.

I posted here in the hope of learning whether others had encountered the same issue or whether Autodesk was aware of any regressions. The issue relates to the use of 3D Sketch in combination with Projected/Included 3D geometry. In my case, coincident constraints to splines sometimes fail silently, to move a handle, I often have to remove the coincident constraint, move the handle, and then reapply it, which is unreliable and inconsistent.

This is a behaviour I’ve never experienced in previous versions of Fusion 360, and I’ve been using it for several years. It’s become a serious slowdown in my workflow and borders on a showstopper for the type of work I do.

While I understand that issues can’t be addressed without reproducible examples, please also understand that preparing a stripped-down demo takes time, time I’m currently lacking, or I would have already done it. I will try to create one as soon as I can.

In the meantime, it would be appreciated if this could be treated as a potentially valid concern rather than dismissed as vague, especially when it comes from a long-time user reporting a change in tool behaviour.

Best regards, Hans

[jeff_strater]

I apologize if that came across as dismissive.  And, thank you for acknowledging that we do need specifics to answer or address issues.  If you spend any time on this forum, you will recognize that we have to deal a lot with people who do submit "vague complaints", and there is very little that we can do about it.  It is hard, sometimes, not to get defensive. 

"whether Autodesk was aware of any regressions"

To the best of my knowledge (and I also use Fusion a lot, and spend a lot of time reading this and other forums), there has been no general regression in 3D sketch functionality, nor have I seen any other indications from customers that there has been any widespread change in behavior.  As @TrippyLighting indicated, "The 3D sketch functionality has never been fully developed and has many open issues", and it is impossible to tell whether the issues that you are referring to are those areas that are not fully developed or not.  Again, specific cases would be helpful.  I understand that doing so takes time, but we need them to return any useful information, or to fix any issues that might exist.

[hansvaneven]

Thanks Jeff for your reply. I’d like to point out that I’m a regular and overall satisfied user of Fusion 360, which I rely on daily in my professional workflow.
My intention is not to criticize the software globally, but to report a very specific behaviour that seems to have changed and now impacts complex projects.

I'll do my best to put together a simplified demo project that replicates the issue. In my case, it occurs within a large and intricate file containing tons of components and sketches, so I hope I’ll be able to isolate it clearly for you.

[hansvaneven]

By the way, just to clarify why I rely so much on 3D sketching. I'm using Fusion 360 mainly for guitar and instrument design, including detailed neck joints, carved tops, and complex transitions (like the heel area or tilted neck pockets). In these cases, 3D sketching allows a much more intuitive and efficient workflow than setting up dozens of 2D planes and projections (at least for me having tested both).

If the 3D sketch toolset becomes more reliable and refined, it could really unlock a lot of potential for users working on organic or multi-axis parts like this. I truly think it's a powerful feature, it's already there, it just needs more love 🙂