topic Re: Mesh body plane cut problem in Fusion Support Forum

Mesh body plane cut problem

Anonymous — Fri, 18 Jan 2019 00:00:53 GMT

Cutting an (STL) mesh using plane cut is now a giant pain cut. It used to work OK, but now it runs slower than cold treacle at the South Pole. Even entering a single digit in Numerical Inputs takes many many minutes, and then it might not take and show a preview. And that process is not intuitive. It should be that pressing Enter makes an key-entry take action, not just keying it, and then when all the key-entries are done, and only then should pressing OK implement them. And I keep getting a message that a Recovery File could not be saved because Fusion is doing a plane cut. !!! I know that; so please do it. But placing the plane in the first place is very hit and miss. There is no indication until it pops up where it is going to choose to set its plane. And using a plane to cut is very crude when all you really want to do is rubber-band a chunk of mesh and remove it, so then you have to fiddle about with changing measurements and angles to get it into the right place. But getting a plane to place the cut is very cumbersome, and may be impossible fit with what you want to do. In my case I have a topographic STL from which I want to remove some bits in the bottom right-hand corner, and because every change in position and angle of the plane takes many long minutes while the disk grinds away doing something, the whole process can take many hours, and then it might crash. A giant pain 😞 Even hitting backspace to change a single digit takes an age, in which Fusion decides what it is going to do, whatever that is. And forget trying to drag the plane/move widget. That takes even longer. And its effect, if it has one, takes so long that you might as well not bother.

Re: Mesh body plane cut problem

jeff_strater — Fri, 18 Jan 2019 01:25:48 GMT

I am confident that Plane Cut has not changed in many months. However, it is certainly true that Plane Cut can be very slow on very large meshes, especially if you use the Fill option. Your feedback on your concerns around entering plane data for fine adjustments to the plane are very valid. Some other expensive mesh commands (for example Remesh) have a "preview" checkbox that determines whether Fusion previews the result. If unchecked, it does not, allowing you to tweak the settings, and only when you are ready to see a preview, and willing to take the time hit. I agree that Plane Cut needs that Preview checkbox as well.

A couple of suggestions in the meantime:

Use a Work (Construction) plane to create your cutting plane outside of the Plane Cut command. That way, you can get the plane positioned just how you like it before you start the Plane Cut command. Then, pick that plane.
Don't turn on Fill until you are happy with the plane, either. Plane Cut without the fill should be a lot quicker than with Fill on.

Re: Mesh body plane cut problem

Anonymous — Fri, 18 Jan 2019 05:34:28 GMT

Thanks Jeff for your prompt reply. After I sent the earlier message I remembered that Fusion 360 sometimes allows/allowed a right-click on the filename, which brings up a menu that includes 'Edit', which allows clicking on individual meshes and deleting them with the Delete key. But 'sometimes' is the operative word; 'Edit' comes and goes.

In the end I solved the present problem by downloading Meshlab, which allows rectangular rubber-banding of chunks, which Delete then gets rid of, so then I loaded the result back into Fusion 360 (would that Fusion had that facility too).

But I then needed to use Plane Cut to cut off the flat base of the object over the X-Y plane, and Fusion was smart enough to guess that the plane I wanted was in that plane across the flat area surrounding the topographical model.

I had created my STL from here: http://touchterrain.geol.iastate.edu/?DEM_name=USGS%2FSRTMGL1_003&hs_gamma=0.7&map_lat=-36.809881715085616&map_lon=175.0885216041811&map_zoom=11&trlat=-36.734430647144805&trlon=175.20731127703266&bllat=-36.85100287326367&bllon=174.9786583229311&tilewidth=200&ntilesx=1&ntilesy=1&printres=0.2&basethick=5&zscale=2&fileformat=STLb ).

As you can see you get a base by default, even at 0mm, so I had to delete it. I wanted first to get rid of the islands in the bottom right, then get rid of that base, then use Make Closed Mesh to make a watertight solid so that all I had was a solid Waiheke Island to insert elsewhere. So Fusion guessed rightly that I wanted to cut off the base across its surface. Well done! And in cutting off the base, Plane Cut worked pretty fast. I just set the X angle to -90 and it was done in very short order. None of the agonising waits when I had been trying to cut the corner off. So the number of facets was not slowing it down when chopping across the X-Y plane, only when chopping down through it.

But a problem remains:

I am now trying to get Make Closed Mesh to work without messing up the low-lying parts of the island. So far I find that picking Accurate, Density 256, and that I need a measure of Offset. How much Offset I have yet to discover. 0.7mm is not quite enough, but there are some dark grey artefacts creeping in, so I am wondering if I am going to get what I want: i.e., the closed mesh looking exactly the same as the original STL, but solid and therefore good for CAM.

That is what I want for positive carving in wood and metal, but I also want to be able to machine a reverse image on the underside of clear plexiglass, so I need to flip the X and Z axes. It looks as though Fusion can do the Z flip using Reverse Normal, but the X??? And I also want to do the same thing with some extruded text. Can Fusion do that?

As you can guess I am new to 3D, although I have been working in 2D graphics for decades, so please excuse what might seem some dumb questions.

Lastly, I love Fusion 360 more and more every day (despite the Pain Cut episode). It is an excellent package, with excellent support. Thank you to all Autodeskers.

Re: Mesh body plane cut problem

Anonymous — Fri, 18 Jan 2019 09:42:39 GMT

Meshmixer's ability to make a solid STL solved the problem. That imported into Fusion has worked. But it does not like being selected for movement, so anything else has to be moved to it.

Re: Mesh body plane cut problem

TrippyLighting — Fri, 18 Jan 2019 15:31:56 GMT

What is the polygon count of this mesh and what do you want to do with it in Fusion 360 that you could not do in Meshmixer ?

Re: Mesh body plane cut problem

Anonymous — Fri, 18 Jan 2019 21:25:37 GMT

It was the other way round. Meshmixer made a solid out of the STL that looks exactly the same as the original shell, but Fusion 360 could not get it right at all. Its effort was distorted and margins were messed up no matter what parameters I used. But Fusion was best for slicing through the X-Y plane, because it placed the slice correctly without having to be told, and did very quickly. But it was impossibly slow when I had attempted to chop off a corner through the Z-plane. That attempt was made before remeshing the object in Fusion. The X-Y- slice was done after, when the polygon count had risen to about 2 million, far more than in the original. So it was impossibly slow with a smaller count through the Z-plane, and quick at a much bigger one in the X-Y plane. Very odd! And it was no good at making an accurate watertight solid. (At this stage I assume Meshmixer's solid is watertight; it looks right, but I have yet to find time to check what happens in CAM simulation.)

I have yet to discover how to make a solid STL if I reverse the STL shell in the Z-axis--i.e., if I make what would look like a mould. For that I would have to make a topographical pocket with the shell in an extruded rectangle. I expect I shall have to use a different technique to achieve what I want.

Re: Mesh body plane cut problem

TrippyLighting — Fri, 18 Jan 2019 21:29:45 GMT

I don't see how you post can be a response to mine.

Nevertheless, what is it that you re trying to accomplish ?

I don't need details, I need the 30 thousand foot view. Based on your answer I can probably suggest an alternative route.

Re: Mesh body plane cut problem

Anonymous — Fri, 18 Jan 2019 21:36:54 GMT

(The reply button in emails doesn't work--it gets a 404, so I go the easy way).

What am I trying to achieve? A positive body that I can mill in wood and non-ferrous metal. And, ideally, a negative as well. By 'negative' I mean what would look like a mould--carved on the underside of clear plexiglass and thus viewed through it.

Re: Mesh body plane cut problem

TrippyLighting — Sat, 19 Jan 2019 11:33:50 GMT

That's what I thought. Cool!

How comfortable are you with using other applications (free and open source) to help you along in this endeavor ?

The image below is a BRep (slid body) in Fusion 360 (not mesh solid as the ones in Meshmixer!) and is editable with the tools in the Model and Patch workspaces. It should also machine quite fine.

Re: Mesh body plane cut problem

Anonymous — Sat, 19 Jan 2019 22:01:15 GMT

Thanks for that technique and the visual proof.

I had tried Mesh to BRep in the earlier stages of my steep learning-curve, and found it wanting for some reason. I shall go back and try it again, but this time using the facilities you have pointed me to. In the meantime I have achieved with the solid-mesh technique--at least visually--what I shall ask Simulation to prove tomorrow.

To answer your question, I have no qualms at all about using any software from anywhere to achieve what I want. I have already been trying all sorts of stuff from all over the place. Fusion 360 is the solid core; I like it very much, but whenever it needs crutches I am happy to use them.

There remains the problem of how to invert a topographical model to make what would look like a mould, a 3D negative, which would be milled into the underside of clear plexiglass, then seen from above as a positive. A flipped topographical 'pocket' would be another way of describing it.

Thanks very much for your help. I appreciate it. 3D means toiling up a very steep learning-curve, which for me was made even steeper by choosing to get my Stepcraft as a kitset to save $$$, and thus forcing myself to get to grips with assembling hardware and learning software at the same time. So helpful advice from someone who has reached a hammock at the top of the curve is appreciated. 🙂

Re: Mesh body plane cut problem

TrippyLighting — Sat, 19 Jan 2019 22:32:23 GMT

I did NOT use mesh to BRep!

As you've discovered yourself, you'd have to down-samle or re-mesh this in Meshmixer or in Fusion 360 to under 20,000 polygons and loose a lot of detail.

I deleted the bottom vertices of the .stl in Blender to end up only with the terrain mesh without the box bottom. I'd believe that is likely also possible in Meshmixer. I am simply more familiar with Blender.
I removed double vertices in Blender. Those are vertices which locations coincide with other vertices within a given tolerance. I am not sure this is strictly necessary.
Then I exported that mesh as a .obj file.
Then I opened that .obj in InstantMeshes and remedied it into a quad-mesh with 2 smoothing iterations.
The result was exported into another .obj.
That .obj was imported into Fusion 360 as a mesh and converted into a T-Spline.
Then it was converted into e BRep.

The trick is to re-mesh the triangulated .stl into a quad mesh. That is a mesh only including polygons with 4 vertices.

The result is a vastly superior surface, compared with the highly .stl triangle mesh.

I can create a screencast later if that helps.

Re: Mesh body plane cut problem

Anonymous — Sun, 20 Jan 2019 00:54:51 GMT

I see. I assumed when you used the word Brep that that is what you had done., using the Fusion 360 menu offering.

But now that you have laid out the detail I see what a long-winded process it was.

Which makes in a different way my original point: that what Fusion 360 seems to offer in its Mesh menu does not work anything like as well as it ought to. It would be better not to have that offer.

I have noticed that the solid body I produced via Meshmixer does not (so far )behave as expected in Fusion 360. It does no select normally; it does not turn blue. But I shall not have time till tomorrow to play with it any more. Trying Simulation in CAM will be the acid test. I shall also have a play with the technique you suggested.

Thank you again.

Re: Mesh body plane cut problem

TrippyLighting — Sun, 20 Jan 2019 03:02:52 GMT

You statement that his just "ought to work" leaves me almost speechless!

The key here is not the missing function of a software tool but knowledge!

The term BRep is easy enough to google. A BRep is a mathematically precise description of geometry including NURBS surfaces. That means these surfaces are resolution free down to the limits of precision of either the CAD system or computer you are working on. BReps also have topology in the mathematical sense. In a way a BRep and NURBS surfaces are the holy grail of CAD geometry.

The .stl mesh created by the online tool you used is of drastically lower quality. In fact .stl files are the least common denominator of all 3D geometry. Meshes and in particular triangulated meshes have a fixed resolution and do not possess the property of topology. They were also never though of as a format to exchange 3D data between applications, they were intended as a pure output format to be used on the earliest 3D printers.

Did you follow any of the links, to the tools I provided ? InstantMeshes was written by students. It is the result of years of study was preset at Siggraph only in 2015 and presents one of the latest technologies to help bridge the gap between triangulated meshes and higher quality surfaces.

I am assuming that for your purposes Fusion 360 is free. Blender ifs free and open software and has been developed for over 20 years. InstantMeshes is free software and also open source. MeshMixer is also free.

After reading the above do you still feel this "just ought to work" ?

Please consider your next response more carefully.

That lengthy process took me 10-15 minutes. Translating a very dense quad mesh into is a computationally expensive process so I had to wait for that to be completed. For a superior result I find that more than adequate!

Re: Mesh body plane cut problem

Anonymous — Sun, 20 Jan 2019 08:59:55 GMT

Sorry, you misread my comment. By 'ought to work' I was talking about using the Make Solid menu item under Mesh.

(And it would be kindness to keep in mind that those of us who are new to 3D do not have the knowledge that you have, and it is therefore reasonable for us to expect English words to mean what they say. Thus 'speechless' is not helpful.)

If I click on a menu item that says the result will be to make a mesh solid, I expect to get that. I expect to get the same thing, looking the same, but as a usable solid not an STL shell. I do in Meshmixer, etc., but not in Fusion 360 (although both are Autodesk products). That is why I said that that option in Fusion Mesh, because it does not work properly, ought not to be on that menu--until it does what it says it does, bug free. People should not have to have a lot of arcane knowledge and thus know that what lies behind the English will mean that you will not get what you can reasonably expect. People should not be expected to know, somehow, that they cannot trust the menu, and that they will therefore have to discover long-winded work-arounds.

I have had decades of experience in 2D graphics, which are obviously far more stable and advanced than 3D stuff (in having universally inter-operable formats, for example), and where simple English means what it says. I am having to get used to a technology that expects a vast amount of work-around knowledge. Those who already have that should be a little accommodating.

Re: Mesh body plane cut problem

TrippyLighting — Sun, 20 Jan 2019 16:01:33 GMT

Ah hah. Sorry, I did misunderstand what you are referring to.

Yes, the naming of the menu in Meshmixer is indeed is very unfortunate, particularly for people that work a cross applications such as Fusion 360 and Meshmixer.

In the 3D world you are not dealing with one industry but two very distinctly different industries that use 3D software for a different purpose.

1. The purpose of CAD software is to create models for manufacturing. That drives the need for the mathematical precision described in my last post and informs how many of the modeling tools and workflows in CAD software are designed. This is mostly the world of BRep and NURBS surface models. This is also the industry that developed the .stl format so designs could be 3D printed.

2. In the beginning models for 3D computer graphics and animation were also created using NURBs surfaces, bot those proved to be difficult to handle and as such polygon and Sub-D mesh modeling software such as Maya and Blender were developed. The purpose of these software packages was to create models mostly for visual representation computer graphics and animation. Here mathematical precision is less of a concern and we are working with meshes that consist mostly of quad faces. Nowadays they are also often used for industrial design and product design.

Both of these industries use triangulated meshes nowadays mostly available in .stl or.obj format, but again mostly for a different purpose. In CAD the sources are often 3D scans with the intention to reverse engineer the original geometry.

Polygon and Sub-D modeling software creates these with sculpting tools.

BTW that is not the Sculpting in Fusion 360, another real unfortunate name, which is really Sub-D mesh modeling and not real sculpting in say ZBrush).

Then there are of course sites like thingyverse where people can stare .stl files created in either software category purely meant for 3D printing these objects. However often enough folks want to modify these .stl files and that can be difficult.

Your landscape mesh falls more into the scan area. The online tool you used scans a 3D data set in and create a mesh form it, which is very uniform in structure, with very evenly sized triangles, which helps creating bette geometry for your purpose. It is so uniform and grid-like that in fact I believe it would be possible to re-write this so it can create a quad-mesh directly.

Once you have that mesh, the question is: What do you want to do with it.
If you only wanted to 3D print it tun could likely send it directly to a 3D printer/slicing software.

As I understand it, you want to remove a particular potion of it ?

For me that is still exactly clear what modifications you want to do and what the best approach is to actually do it.

Do you want to cut off a section to remove part of the terrain you are not interested in - this would obviously alter the rectangular/box shape of the object, or do you want to maintain the rectangular shape and just flatten a particular part of the terrain to blend in with it's surroundings.

The next question to answer is what do you want to do with the object or bore specifically, if you want to "make" it, by what means. You've already answered this, but I'll go over this anyway.

You can directly machine .stl files in Fusion 360's CAM package, but I don't have experience in that area. Maybe @LibertyMachine or @HughesTooling can answer that.

However, a mesh is a mesh and it will retain its faceted nature. If the mesh resolution is relatively coarse and depending on the method of manufacture this can be seen in the end product and often that is not desirable. Thus we'd want to smooth the mesh. This is done by re-meshing a (semi) automated form of re-topologizing the triangulated mesh into a mesh consisting only of 4-sided polygons. The key task is really yo re-create topology.

That's what I used InstantMeshes for. There are other a number of tools that can do this, but not all of them are available for free.

Once we have that quad-mesh, then we can still decide to work with it in a Sub-D modeling application egg, Maya or Blender, but I won't go into detail here why that may make sense. Or we can use that quad mesh to get to. NURBS surface. NURBS surfaces and Sub-D surfaces share some mathematical similarities.

In case of Fusion 360 the intermediary step between and an imported quad mesh and a NURBS surface is a T-Spline.

As discussed already we end up with a NURBS surface, a mathematically precise description hopefully close enough to the original mesh.

The surface and in the case of the solid model I showed in a post above can then be machined in the CAM environment.

While this is not widely known it is not "arcane" knowledge by any stretch of the imagination. There is nothing secret, or mysterious about it and it can be easily found on the internet if you know the proper terminology and are able to connect the dots between new different technologies and methods. There are plenty of detailed research papers such as the one published on the project page for InstantMeshes.

However, your project resides more on side of the CAD industry and quite frankly, the majority off CAD users are fairly uninformed about such topics. They have gotten so used to things just working out that they've stopped understanding sometimes of even the most basic underlying principles of the tools they are working with. People that use Sub-D molding tools are generally much better informed about the underlying technologies used in their tools than the usual CAD hobbyist and many professionals and as such there is not much information about it in the CAD sphere.

Re: Mesh body plane cut problem

Anonymous — Sun, 20 Jan 2019 21:39:56 GMT

Thank you, Peter, for your long patient explanation.

One phrase that particularly stood out was this one: 'You can directly machine .stl files in Fusion 360's CAM package', because the reason I have been trying to find the process to turn an STL shell into a solid body for milling in CAM in wood and non-ferrous metals is that one of the many very helpful YouTube videos produced by an Autodesk guy called Lars Christiensen said that an STL cannot be machined, only 'printed', and therefore we must go through a process to convert it, a process he outlined. Perhaps I should have ignored that, and tried it, because my long history in computing has found from time to time that just doing something works. So I shall see what happens. Ignorance can sometimes be the road to discovery... 😉

Another phrase that stood out was your use of 'an unfortunate name'. I am glad that even a 3D ninja like you sees some mismatches between terms adopted by different software engineers, and between them and the Oxford Dictionary.

Perhaps it will help if I say in different words what I am trying to extract from the original satellite download of an island surrounded by sea, a download which has to include some smaller outlying islands. I want to extract just that island, devoid of sea and the outlying islands. So I have to chop off the outlying islands then slice off the sea, which leaves me with just the island I want, which I can then marry to whatever body I choose, mainly as a millable convex positive but also as a concave negative.

I did manage the chopping and slicing, which CAM liked reasonably well in Simulation, but the result was not the resolution I wanted. So the second attempt, which is as sharp as a tack has also been managed. Now I shall try Simulation to see if CAM will work, while I await the collets I need for my Stepcraft. I shall try it with raw STL, given your comment above, and also with my extract married to another body.

Re: Mesh body plane cut problem

TrippyLighting — Sun, 20 Jan 2019 21:52:03 GMT

@Anonymous wrote:

Thank you, Peter, for your long patient explanation.

One phrase that particularly stood out was this one: 'You can directly machine .stl files in Fusion 360's CAM package', because the reason I have been trying to find the process to turn an STL shell into a solid body for milling in CAM in wood and non-ferrous metals is that one of the many very helpful YouTube videos produced by an Autodesk guy called Lars Christiensen said that an STL cannot be machined, only 'printed', and therefore we must go through a process to convert it, a process he outlined.

He did make another video after that ability was added:

Having said that, I believe the method of converting a .stl into a smooth NURBS surface can still possibly produce better results and also enables you to do things that otherwise would not be possible.

Re: Mesh body plane cut problem

Anonymous — Sun, 20 Jan 2019 22:49:36 GMT

Thanks for that, Peter. I have looked at or marked many scores of videos so far, including many by Lars, but that was one I had yet to come across. After seeing what he is doing there it looks as though I might be able to use STL directly to do my concave version by inverting in Z then flipping in X. His little hints, such as use 3D not 2D, etc., etc., are gems. Experiment will tell...

I find Fusion's pop-up information notes very helpful, as I am sure many do, so it occurs to me that going one step further and having scripts tied to FAQs would be nice. For instance, if we were to ask how to do CAM on STLs, it would bring up a step-by-step script, which would take us through the right process, moving down a line as we completed each one. Lars in a script, like an airline pilot's checklist.

Re: Mesh body plane cut problem

TrippyLighting — Mon, 21 Jan 2019 02:45:07 GMT

@Anonymous wrote:

Thanks for that, Peter. I have looked at or marked many scores of videos so far ...

I made this one today so here's another one you can add to your collection :

Re: Mesh body plane cut problem

Anonymous — Mon, 21 Jan 2019 06:25:15 GMT

Wow! You are worth your weight in platinum, Peter. That video is one to keep. Thank you for taking the trouble to make it.

I had already discovered and tried the erasing brush in Meshmixer to get rid of the unwanted islands, but using it left some slightly-raised artefacts in that corner, which I had to chop off, which I did in Meshlab, otherwise I was left with some unwanted 'noise' when I sliced off the base that the terrain site includes.

I shall download Blender and Instant-Meshes to add to my arsenal. I noted in passing the ability of Blender to squash a body in the Z direction etc.. Very useful. I had been looking for that ability.

I now understand something I had not understood before. As I have said I have long experience with 2D graphics, and there of course I work in bitmaps and vectors, sometimes one, sometimes the other, sometimes a mixture in the same graphic. I now see that STL and other meshes are the 3D equivalent of bitmaps, because they have a fixed resolution, like the holes in a fishing-net, and that T-splines are 3D vectors, so they have infinite resolution, and are therefore, as you say, the best format to use. They can be enlarged for ever without losing detail, like T-fonts.

So in my own mind I shall call them 3D vectors, which is a much more friendly term than T-splines or NURBs. Meshmaps and 3D vectors. That keeps my head on familiar ground, but I shall have to remember to translate into 3D gobbledegook when talking with 3D ninjas.

I have one question, based on what you did towards the end of the video. If you had cut the cylinder with the T-spline the other way round in the Z-axis, would you have ended up with, in effect, a mould of the terrain? A body that I have been calling a negative?