Major issue working with mesh files

[oldrebelworkshop]

First off, I'm a hobby user supporting my model railroading and fishing habit.  I often download (legally) mesh files from various site's, with the intention of making changes (some small and some significant), and then export them for 3D printing.  When I am able to convert the file to a solid, I generally have no problem, but many of the files are too large to convert, so I end up working with mesh files, and that's my problem.    When executing a "Combine" in the mesh workspace, it takes my computer several minutes, sometimes hours, to complete, if it in fact completes at all.   Sometimes I have to exit out of the program, and start over.   At first, I thought it was my computer, so I replaced it last year with an up to date system, running Windows 11, 32 GB Ram, and 8 GB video, and all drivers are up-to-date.  My internet connection is fiber, and lightening fast, both up and down.  I've tried to search through the forums to find similar problems, but to no avail.  I am self taught on Fusion 360, and have been building objects from scratch for a number of years, with few issues, but I'm far from a techie.  I know just enough about computers to be dangerous, but lack the necessary knowledge to go beyond following dot to dot instruction.   I know I have not provided much definite information, and no example of a file I am having difficulty with (it was too large to attach).  I'm just hoping someone might have ideas on what I can try to fine the problem.

Old Rebel

[johnsonshiue]

Hi! Mesh is an imprecise representation of a model. I suspect the mesh you are working with is from scanned data, which may suffer from even more imprecision. It is almost impossible to make imprecise data precise. But there are workflows to mitigate such imprecision. I suggest you simplify the mesh (by reducing the mesh element count) and group the mesh objects. Use Repair, Reduce, and Remesh commands to cut down the complexity. It will be an iterative process. There is a one-size-fits-all solution to make it work.

Please feel free to share an example here. We have quite a few mesh modeling experts on the forum to help.

Many thanks!

[TrippyLighting]

Meshes are not how CAD software represents 3D geometry internally, for good reasons!

CAD software uses Analytic geometry or NURBS to represent  3D geometry.
Analytic geometry is the study of shapes that can be represented by relatively simple formulae. Spheres, Boxes, Cones, Tori, etc. NURBS are used to represent arbitrarily curved surfaces. 

In most mainstream CAD software, those are stitched into a BRep. Those are your solid bodies in Fusion.

The key here is that those are all mathematically precise representations of 3D geometry with effectively infinite resolution. They also have topology. 

Meshes, on the other hand, and in particular triangulated meshes, have a finite resolution and often little or no topological information. CAD software can convert a solid or surface model into a triangulated mesh representation, but it is difficult, and often impossible, to reverse-engineer an object to its initial mathematical precision from a mesh.

Unfortunately, in Fusion, you can convert a mesh directly into a Solid Body. All triangular facets are converted to analytical surfaces and stitched into a BRep. That creates a much larger data model. Particularly when continuing to model problems with near-coincidence and near-tangency can make modeling difficult. 

Also, modeling operations take much longer to compute. Let's model a solid cube and then use the hole feature to create a cylindrical hole through it. Fusions have to calculate two surface intersections. 

Now you convert the cube into a mesh, then into a solid body, and the hole takes longer to calculate because Fusion might have to compute a few hundred surface intersections.

If you model with high-polygon-count meshes in the Mesh tab you can also use the combine feature. But the higher the mesh count is, the longer it takes.

BTW, I have posted this on this forum so many times in response to the same or similar problems that I stopped counting years ago. Not sure why you couldn't find anything similar.

If you can post a screenshot of what you're working with, we can provide more targeted advice. Not all meshes are created equally, and there is a whole zoo out there. Different meshes might need different tools to work with.

[TheCADWhisperer]

@oldrebelworkshop 

There are no curves in stl mesh files, only straight lines and planar triangles.

There is no inherent reason stl can't be good geometry for stl printing, but the fact is that many users are "less than diligent with quality concerning mesh because they might get away with it".

If you are interested in quality work, then I would use someone else's mesh only as reference in creating quality geometry.

[Drewpan]

Hi,

I also have run into problems with converting meshes to fusion solids. I use the

Tools in Fusion to simplify the Mesh and reduce the triangle count. As stated in the

other messages in this thread, meshes are NOT CAD, they are representations of it.

By reducing the triangle count you are discarding information and simplifying the

number of calculations that fusion has o make to convert it. Unless you really do

need extreme precision dumping 90% of your triangles will be unnoticeable to

the naked eye in most cases, If you DO need precision then Meshes are not a good

starting point either. 3D printing is usually only precise to a tolerance of 0.1mm

at best for FDM. Some SLA printers are better but not perfect. Dumping triangles

to only a few thousand instead of tens of thousands will make a big difference.

Cheers

Andrew 

[oldrebelworkshop]

Thanks for your reply. Unfortunately, I don't have any formal training in
CAD (or Fusion), and as a result, don't have the skill necessary to make
many of the things that I need. In many cases, it's much easier to use
someone else's model and change it for my needs. In the case of more
complex models, I generally just move on to something else.

[oldrebelworkshop]

Thanks for your reply, Andrew. I've tried reducing mesh files to fewer
triangles, but often run into problems where I still can't get the size
reduced enough to convert to a solid. Also, many times the end result does
not even resemble the mesh that I started with. Is there a particular
method you use to get the reduction in size?

[TrippyLighting]

---

@.. Is there a particular
method you use to get the reduction in size?

---

If you can share at least a screenshot of a mesh we can be of more help. Reducing a fixed-resolution mesh often reduces detail , which is often undesirable.

There are other methods to convert meshes into solid models or surface models. As I mentioned in my post, not all meshes are created equally.

A scanned mesh, for example has lost all of the topological information that software like Fusion can use to re-create the original geometry. They may exhibit scan noise, have open areas and self intersecting geometry. 

Meshes that are exported from CAD software usually have some remnants of topology.  

Meshes created by Sub-D mesh modeling software have a visually different topology and sometimes are easy to convert.

A screenshot or actual mesh would help.

I don't recall having ever had formal CAD training ... OK, once over 30 years ago for one week. CATIA in 2D. 

If you're interested in learning, that is what this forum is for, albeit not particularly formal 😉

[oldrebelworkshop]

Thanks for that info. I'm starting to understand why my approach works
sometimes (simple mesh) and not at other times (more detailed mesh). With
no formal training in CAD, I've adopted the "Bible" method, (Seek and Ye
Shall Find), to gain possible answers, (mostly u-tube or Fusion Help
files. This is my first attempt at asking for help in the forums, and I
was like a lost ball in the high weeds at finding what I needed; probably
because I had no idea what I was doing, so I apologize for not finding your
previous posts. Attached is a screenshot of what I was trying to
accomplish (eventually successful after hours of trying). The minnow is a
mesh file that I had downloaded. I was attempting to make a 3D printed
mold for casting a soft plastic fishing lure with 2 part silicone. I
created a box (solid) the size of the mold. After trying unsuccessfully to
reduce the size of the minnow enough to convert to a solid, I converted the
solid box to a mesh and proceeded to combine (cut) the minnow out of the
box. When that finally completed, I did a 'plane cut' to separate the box
into 2 pieces, then made a loft (in solid), converted that to a mesh, and
combined (cut) that out of the mold where I will fill the mold with liquid
silicone. And last of all, I added 2 alignment pins to keep both sides of
the mold in position during the silicone pour. Used the same method as
before, pin in solid, convert to mesh, combine (add) to mesh.

End result, I achieved what I set out to do, but what I thought (at the
time) was a simple task, took up most of my day. Lots of trial and error;
now I understand why. From a knowledgeable standpoint, would you provide
some insight into the preferred method to accomplish this end result.
Finding a solution to this situation would solve 90% of the problems I have
with Fusion.

Again, Thanks for your help.

[TrippyLighting]

No screenshot was attached. The best way to post screenshots in NOT to attached them, it is embedding them.

You can drag an image/screenshot directly from a folder into the post.

[TheCADWhisperer]

@oldrebelworkshop 

If you are using email Reply to try to attach files - that does not work. You must use the web forum.

[TheCADWhisperer]

---

@oldrebelworkshop wrote:
I don't have any formal training in CAD (or Fusion), and as a result, don't have the skill necessary to make
many of the things that I need. 

---

The experts here freely offer their help in learning how to use Fusion.

---

@oldrebelworkshop wrote:
In many cases, it's much easier to use
someone else's model and change it for my needs. In the case of more
complex models, I generally just move on to something else.

---

It isn't easier if it doesn't work and you have to abandon.

The easy way to learn to use Fusion.

The experts here will freely help you do that - then you will not have to try to work with someone else's rubbish.

[oldrebelworkshop]

When it comes to solid geometry, I can usually build what I need. My
biggest struggles are working with Mesh files. I'm sure there must be
tutorials on working with mesh files. I think I need to find some and
spend time learning about them. I don't use them very often, but I do need
to learn how to handle them.Appreciate your help.

[oldrebelworkshop]

Body3 and Body3a are the .stl's I ended up with. Both 3D printed without
issue.
Body3.stl
<>

Body3a.stl
<>

This is the original .stl that I started with.
lambari2b_split.stl
<>

Hang with me guys. I'm learning as we go. Really appreciate
your willingness to help an old rebel.

[TheCADWhisperer]

---

@oldrebelworkshop wrote:
My biggest struggles are working with Mesh files. I'm sure there must be
tutorials on working with mesh files.

---

Mesh files are commonly rubbish.

Everyone's biggest struggle is trying to work with rubbish.

Like trying to bake a cake from the contents found in a dumpster behind the bakery.

[TrippyLighting]

---

@oldrebelworkshop wrote:
Body3 and Body3a are the .stl's I ended up with. Both 3D printed without
issue.
Body3.stl
<>

Body3a.stl
<>

This is the original .stl that I started with.
lambari2b_split.stl
<>

Hang with me guys. I'm learning as we go. Really appreciate
your willingness to help an old rebel.

---

If you attempted to attach anything, it did not work!

I still don't see any images in your posts, or files attached to any of your posts.

Is this the model?

thingiverse.com/thing:6404908

If so, what do you want to do with it?

[Drewpan]

Hi,

As has been suggested, working with meshes is not optimal in many cases. If reducing the

triangle count is not working then I think the best suggestion is to have a go at doing it

yourself. This is not as hard as it seems. Fusion has some excellent embedded tutorials

in the documentation and the basics of modelling can be learned in a few hours. The

AutoDesk site also has some great Self Paced Learning projects to back up the tutorials.

This is how I learned fusion. You will never stop learning and even some of the Gurus learn

new things from time to time and they are always here to help if you run into difficulty.

I couldn't draw to save my life until I learned technical drawing and CAD was a very simple

next step. These days you "don't need" to learn Tech Drawing to learn CAD but from my

experience knowing how to do something on a flat sheet of paper helped solve some of

my CAD issues. I started with 2D CAD which is really Tech Drawing on the computer screen.

Modelling is different and there are a few things you do differently.

The secret to getting good is practice. I am a Student and I do all of my school work on

fusion but I also practice models for fun and to learn new techniques. I am no Guru but I

help out a lot on the Forum simply by passing on what I have learned. Simply put - you will

get out of fusion based on what you are prepared to put in.

There is a time and place for most things and meshes are useful things but they are not

always the solution. A good CAD Model will almost always be better than a converted mesh.

Hope this helps.

Cheers

Andrew

[oldrebelworkshop]

That's the one. I cut it out of a box then split the box, to make a 2 part
mold for a fishing lure. I was finally successful, but each step took up
to 30 minutes to complete, with several that failed and had to be started
over. When I tried to add the files into the body of the post, it showed
them being attached, but indicated they were too large, and was being sent
as a link to Google Drive. First time using that too. Thanks for sticking
with me. If I can find a solution to converting a mesh to a solid, 90% of
my Fusion problems will be resolved.

[TrippyLighting · Accepted solution]

---

@oldrebelworkshop wrote:
... If I can find a solution to converting a mesh to a solid, 90% of
my Fusion problems will be resolved.

---

Or you might just approach this the wrong way 😉

Converting a mesh to a solid and then continuing to model with a highly faceted slid is computationally very expensive.

You could, on the other hand, convert the solid models for the mold halves into a mesh:

Then, instead of using the solid modeling combine feature, you could use the  combine feature in the Mesh tab:

There is no loss in fidelity of the model, because the input to your design is a faceted mesh.
The resulting mold halves are also meshes, but meshes is what you are 3D printing anyway.

[oldrebelworkshop]

Right, that's how I finally got the mold completed for printing. Due to
the size (I suppose) of the mesh, every step just takes a very long time to
complete. I had hoped there was a better method of converting a mesh to a
solid, as solids are what I generally work with. I guess it's time I
learned more about working with meshes. I certainly appreciate your help.
I now understand more than I did, but still got a long way to go. lol.