3D Sketch Problem or Newbie Inexperience?

[Anonymous]

The drawing is done on the XY plane. The long arc is drawn on a YZ construction plane, and each of the transverse arcs has a dedicated construction plane on the XZ axis. I'm too new to know if creating this many construction planes is a good practice or not, but it was the only way I could get it to work.

Look at the portion of the sketch that does not have faces on it. I don't know exactly how Fusion 360 made the connection between points on different planes, and I didn't know if it is possible to tell Fusion to look on multiple planes. I didn't use the project function since projecting in 3D sketches is not well-covered in the online tutorials, and I was lost. This might have affected some steps I took later, but I plowed along until I got to the point you see in the attachment.

When I attempted to draw the transverse arcs, Fusion could not find the the reference points with the 3-point arc command loaded. By accident, I discovered that when the line command was loaded, most of the points were recognized, although not all. I drew a straight line between the points, and after that Fusion found the points with the 3-point arc command active. So, I drew the arcs and then deleted the straight lines. Seems like a very convoluted way to get the results I wanted. Is this a bug, or did I just do something wrong?

[davebYYPCU]

If you are not using the Project commands, you have one hand tied behind your back.  For each Sketch, you can project the intersection for each curve that penetrates the sketch plane.  You receive the purple points to connect to.

As all the sketches appear to be 2d, I am not sure of the question, certainly 3d sketches have limited functions, where 2d are logical.  That you have 32 visible Sculpt icons, then you are taking the harder approach, when the top face would likely be one body.

Something to think about....

[Anonymous]

Thanks for the reply, davebYYPCU--

According to all the tutorials I've seen that touch on the subject, Fusion 360 treats all sketches as 3D sketches. Since my sketch goes across more than 20 construction planes on all 3 axes, I'm assuming that it's 3D. If it isn't, that would go a long way toward explaining some of my problems.

I guess the first question to which I'm trying to find an answer is why Fusion can't find a point when I've loaded the cursor with the 3-point arc command, but finds it easily (ah, that wonderful little blue square!!) when the cursor's loaded with the line command. And why, after I draw a line from that point to another, Fusion finds them both with no apparent problem when I try the arc command a second time. Is this some known issue?

--Bob

[TheCADWhisperer]

File>Export and then Attach your *.f3d file here.

[davebYYPCU]

In theory that statement if treating all sketches the same way under the hood, is a - dead end rabbit hole I don’t want to go down.  The sketch solver has some bugs with mostly complicated sketches.

For a newby, stick to 2d sketches, until you can’t.

one sketch per feature.

features the require more than one sketch, Sweep and Loft, one sketch per selection, until you learn the ropes.

The little blue snap box, yep that’s exactly what you need.  It works reliably with connections within the current sketch, and totally random if connecting to items not in the current sketch.

Sooo if you need to connect to an external item, Project it into the current sketch.

Might help....

[Anonymous]

This is going to seem totally dumb (and it probably is), but I can't find the file on my computer. I was under the impression that Fusion 360 kept files both in the cloud (permanently) and on my local disc (for a period of time). Can't recall how long a time, but certainly longer than the time between our two posts. Not sure how to download it from the cloud to you, or download it from the cloud to me, and then to you.

--Bob

[Anonymous]

OK, It took a long search, but this was waiting for me when I cam back to my screen. Hope this works.

--Bob

[laughingcreek]

Is there a particular reason your using the sulpt environment in the manor you are using it? (one little section at a time).  You are going to have a very difficult time achieving a desirable result with this approach.

I have created many arch top guitars and similar instruments using both tradition lofting techniques and the sculpt environment.  These days I tend to gravitate towards using sculpt (t-splines) because I find it easier and faster.  But It isn't done square by square.  you have to set up the topology of the t-spline properly to get a desirable result.  That takes a bit of experience.

As an aside, which environment you are in (model vs sulpt) when you create a sketch has an impact on your workflow.  The sculpt environment isn't parametric.  Sketches created there won't appear in the timeline, and if you project anything into those sketches, the projections won't update when geometry changes.

[Anonymous]

Yes, there is a reason I'm using the sculpt environment in the way I'm using it. The first is that I'm too inexperienced to know yet if there's a better way, and the second is that the use of planes for musical instrument arching is what James Cherry describes in his YouTube video series, and also the way Lars Christiansen recommends in his Fusion 360 tutorial series. And that's about all there is out there in the way of tutorials.

That said, pulling planes from planes and manipulating them around the perimeter of the instrument is highly inaccurate. What I've done creates a 3D wireframe of the arching that I intended to use as a reference to place the planes. This kind of accuracy is why one uses a precision CAD program, but it seems none of this applies in the sculpt environment (or whatever they're calling it these days).

I can't find a way to snap points on the planes to points or lines in my drawing, so I'm back to doing things by eye. I tried using faces as well, but even though I can snap to lines and points and place faces with better accuracy, I can't seem to edit them and Fusion bombs me with error messages. Fusion's insistence on the use of constraints and of the timeline only serves to make my task much more difficult. This makes the advantage of parametric design of little use in my case.

Each square of the 3D grid accurately describes a single portion of the arch, and as you can see, they are all different. My assumption was that the individual planes could be joined together at the end to form a solid, but you as well as others do not seem optimistic about my chances, which is worrisome given the amount of time I've invested. I am willing to try anything at this point, and any help will be gratefully received.

The goal of the exercise is to cut the rough archings of the instrument on a CNC machine since a long history of shoulder injuries greatly reduces the number of hours I can work with a heavy gouge. If you've ever made a contrabass, you can see where this is going. As much as the model environment (or whatever Fusion is calling it now) frustrates me, I really like the CAM portion of the program (or whatever they're calling it now). It's been a joy to learn, and I have trouble believing the sketch and model parts of the program and the CAM part were written by the same people.

I'm rambling. Sorry . . . 😊

[TheCADWhisperer]

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@Anonymous wrote:

Yes, there is a reason I'm using the sculpt environment in the way I'm using it. The first is that I'm too inexperienced to know yet if there's a better way,

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I don't think that you will ever get satisfactory results using your present technique.

Step away from fusion for a minute and imagine:

- you have a real instrument in front of you.  You take a sheet of material and drape it over the instrument.  Better yet, the material can heat shrink to form (only considering the top for now, not the sides and the sheet itself extends beyond the part boundary) without any creases in the material.

So I think what would work best is overbuilding sheet (bigger than final form rather than attempting to model final boundary) with Loft Surface.  Then Trim-surface the boundary edge.  Not sure if Trippy or someone else has a link to relevant tutorial, but this is the technique that I would use.

Here is an example image that I used this process to define the shape of a toy car (only one of the overbuild sheets shown).  One advantage is that it is very easy to edit.

Another image...

[laughingcreek]

If you post links to the tutorials you are using for reference, it can help us better understand where you are coming from.  The approaches you describe sound sub-optimal.

I've attached a quick example approach using a single t-spline (that's what your working with in the sculpt environment).  This was just a quick example, so it still needs  some refinement.  you can further edit the t-spline and adjust point positions and add edge loops to get it more accurate.  basic idea here was to overbuild the surface, and replace the face of a solid with it.

Looking at your profile curves, they have the feel of imported curves.  Did you draw these originally, or import them?  There are some issues with them.  I would at least go back and make sure all the endpoints are touching (they aren't) and restrained with a coincident restraint.  and the arcs should have tangent restraints.  (I would actual go back and redraw all the profile curves using mostly splines.)  Fusion needs good sketches, and doesn't play well with imported curves.

[TrippyLighting]

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@Anonymous wrote:

... that the use of planes for musical instrument arching is what James Cherry describes in his YouTube video series, and also the way Lars Christiansen recommends in his Fusion 360 tutorial series

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Can you provide links to these specific tutorials ?

If you rely on youtube alone for tutorials and information then good luck. You'll need it 😉

There is a Fusion 360 Luthiers group on Facebook which might interest you.

There are a whole host of guitar building threads on this forum that discuss every available technique on how to model specific aspects of stringed instruments.

[Anonymous]

Good Morning, and thanks to those who have come to my assistance! 😀

Here are the links to the violin arching sculpt "tutorials" on YouTube. FYI, James Cherry is a luthier based near Salt Lake City. Lars Christiansen works for Autodesk and is (or was) on the Fusion team. You can see that both recommendations are nearly identical, but if you have experience in musical instrument arching you can also see the places where it would become greatly inaccurate.

https://www.youtube.com/watch?v=B6LujVM-R8s  (Lars)

https://www.youtube.com/watch?v=nrXuHSPQZKE&list=PLtoC5TIxpwGVqkF-15_RME3sb-zUpGnRG&index=6&t=0s (James)

I wasn't trying to put an edge on the arching portion of the drawing shown in the screenshot I posted. It's an unfinished drawing, but my idea was to do the outline, which is flat, using the techniques shown in the videos. Then I was going to merge all the individual planes into one and thicken everything by 4 mm. This way I'd cleverly have both the interior and exterior arching in a state that would allow me to use the same drawing for creating G-code in the CAM part of Fusion. Somehow haven't quite celebrated my cleverness yet.

The entire sketch in my project was drawn in Fusion. Nothing's imported. I didn't know some of endpoints weren't touching, but I'm not surprised. In my original post I noted that I couldn't use 3-point arcs without first tricking Fusion by using straight lines from point to point, but the results were inconsistent. In browsing this forum, I have read complaints about the 3-point spline command not working that go back to 2016, so this is a problem Autodesk has known about for years and apparently has not corrected. Of course, I always leave room for operator error as being the main culprit here. That's why I need and appreciate all your helpful experience.

I had wondered why lofting would not be a viable route given that the arching arcs might make perfect rails, but in the YouTube tutorials every time a loft was done it was to a 3D object, and I wanted to do it in a sketch. If anyone wants to post a tutorial about this, you might be the first!

[Anonymous]

Thanks for the post, Trippy--

Most of the luthiers forums I've come across are weighted toward electric guitar making. It's basically flat stock with contour and pocket CNC operations predominating. I've made molds for contrabasses from Fusion360 drawings I made. I used 3/4 plywood sheets, and it's pretty straightforward. Complex arching is an entirely different animal. Any leads you can give me toward acoustic archtop sources, either violin, mandolin, or guitar would be a wonderful find. I still have a lot of hair on my head that I haven't torn out yet, and I'd kinda like to keep it there! 😊

--Bob

[TheCADWhisperer]

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@Anonymous wrote:

.... I still have a lot of hair on my head that I haven't torn out yet, and I'd kinda like to keep it there! 

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And your using Fusion???

🙄

[TrippyLighting]

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@TheCADWhisperer wrote:

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@Anonymous wrote:

.... I still have a lot of hair on my head that I haven't torn out yet, and I'd kinda like to keep it there! 

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And your using Fusion???

🙄

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Ha Ha ha, good one!

[TrippyLighting]

Most, maybe. Not every thread here on the forum discuss guitars either 😉

@jeff_strater had a nice list going with applicable threads to guitar/instument building, but honestly such a list should not take longer than an hour or 2 of research here on the forum and is well worth it.

What you should be focussing on is not tutorials that discuss how your particular class of objects is created. Focus on concepts, then technique:

How to create proper splines/curves and what even is a "proper" spline/curve ?

How are surfaces created from curves and what properties do they have ?

What is a T-Spline and how to model with it (forget most Fusion 360 tutorials on that topic) ?

etc.

Can you provide links to the tutorials you named in one of your posts above 

[davebYYPCU]

The links in message 13 don’t work? or did you miss those?

[Anonymous]

Yeah, but instead of Fusion 360 I've been inclined to think of it as ConFusion 180. That's because the program and I "think" exactly out of phase. For example, when I draw a line in a sketch, I want that line to be nothing more than a line and to stay where I put it. When I want to move it or constrain it, I want to do it myself when I'm ready and not have Fusion constantly putting in constraints to "help" me. When I started with the program not all that long ago, Fusion was maddeningly cavalier about showing all the constraints it added, so I'd try to add tangency to some arcs, the program would chug away for a while, and then my entire sketch would go off in a hundred different directions because I couldn't tell that lines here and there still had constraints on them.

There's a lot of power under the hood of this program, but getting that @#$%^!* hood open is a frustration! Oh, well. We press on regardless . . .

[Anonymous]

I'm not following your question (I think) ☹️--

Regarding message 13, did you mean that the links aren't working, or were you asking if the techniques shown in the links weren't working. Or perhaps it's my brain cell (singular) that's not working . . .