Author Topic: Does anybody here export STL or OBJ format for 3D printing?  (Read 3050 times)

adriank

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #30 on: December 03, 2017, 05:41:33 PM »
BM,
Sketchup automatically fixes what it sees as issues (I've attached the report). The first thing on the list is a layer issue that SKP has with every file exported. It seems DCad creates an extra layer on exporting that has no name, and SKP freaks out at layers with no names - the layer & content is still there & I just have to manually name the layer.

I've also attached the result in SKP which appears fine - BUT, I also tried re-importing the SKP file back into DCad and then it got messed up! The missing faces are not the same as you had experienced however. I don't know if that offers any clues to you clever people out there...

BlankMan

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #31 on: December 03, 2017, 06:01:35 PM »
Lar you don't get it. It's a DesignCAD problem. If you don't believe me ask DrollTroll.

By the fact that DesignCAD 3D MAX 2018 now stops and tells you when an object is no longer water tight meaning it's non manifold that tells you right then and there you're probably gonna have a 3D printing problem. And you know what? It's right.

How can you say it's not DC3's problem? You just became an expert on what 3D printing slicers require?

And most slicers fix things and you don't even know they're doing it. But the likes of these problems in DC3 exports go beyond what they can fix.

As I stated, your Cinema 4D and Sketchup and a multitude of other software apps will open and display problematic, non-manifold STL and OBJ files just fine. Making it look like the files are fine when they're not. I have a bunch of viewer apps and I can take any of those bad DC3 exports and open them up in them and show you they look just fine there.

I've stated this a number of times now. So move past this please.

It's been a DC3 problem, IMSI knows it, IMSI has told me so, Kevan has told me so, and It's also why DC3 2018 itself tells you so now.

As far as backface culling goes these problems are not due to flipped normals they're due to triangulation errors which Kevan has told and shown me that DC3's triangulation algorithm has problems. I can send you the email from Kevan if that will help finally convince you...
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BlankMan

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #32 on: December 03, 2017, 06:11:11 PM »
Thanks Adrian,

That report that I see posted, one page, that was all the errors? When it fixed the errors can you then export a fixed OBJ or STL file? I'd be interested in importing them into Simplify3d and see if that helps.

Smiplify3D as with most slicers can and do fix a lot of issues by themselves, but these DC3 exports they sometimes can't.

From the looks of that import back into DC3 it's hard to see that it fixed a lot. :-)
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adriank

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #33 on: December 03, 2017, 07:53:17 PM »
Yes, that was all the errors.
SKP has bugger-all export options I'm afraid - the question is whether the CAM software has the option to import SKP files.
As I said before, I have no idea about 3D printing but the machine shop I use was able to handle SKP files to do some 3D routing for me recently.

Lar

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #34 on: December 03, 2017, 08:22:21 PM »
Well, BM, I've done as much as I can so I wish you luck.


Just for the record, my last STL was actually exported from C4D, not Dcad. When imported from Dcad into C4D it had 1647 points, 4943 edges and 3255 polygons. I then selected all the points and 'Optimized' at a tolerance of .01", meaning all points that were within .01 of an inch of each other were melted down into 1 point, the separate edges of those melted points got melted into single edges and any polygon caught between melted edges got eliminated. After optimization it had 1131 points, 3402 edges and 2235 polygons. I then STL exported from C4D and that's the file I uploaded. So it seems IMSI is not the only company with problematic algorithms.


Lar

BlankMan

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #35 on: December 04, 2017, 07:46:29 AM »
Lar, here is proof it's DC3's problem. In DC3 itself here is it itself showing the problems with it's triangulation.

A rogue line connection to nothing. Squares formed not triangles that then form "T" junctions not vertices.

Sorry but the fact that you reduce your mesh and can tell me the points edges and polygons has no real value addressing the subject at hand which is DC3 having problems triangulating.

The fact that mesh can be reduced does indicate a software problem. The less granular it becomes the less smooth it is. Again that does not matter to viewing apps because they smooth the surfaces to make it look nice for you. But a CAM system like a 3D printer or a CNC is going to make exactly what you tell it to make by following the triangles. Less points edges and polygons = a more faceted surface.

I've seen it happen when I've made curves arc circles etc. in DC3 and had NFace too low. Or when you take a OBJ or STL and increase it's size by 1000%. The facets get bigger but still look great in a 3D viewer due to its smoothing but when you turn it into a physical entity you see all the facets and edges.



« Last Edit: December 04, 2017, 08:09:02 AM by BlankMan »
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BlankMan

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #36 on: December 04, 2017, 07:56:02 AM »
Thanks Ardian,

Smiplify3D says:

3D Model Files (STL, OBJ, 3MF): Output from CAD Software
Toolpath Files (GCODE, X3G, MAKERBOT, 3W, G3DREM, BFB)

Does say Output from CAD Software but doen't say Sketchup in particular. I'm pretty sure a lot of people are drawing what they make in Sketchup so I'll have to see how they're then creating STL files of their drawings.
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Rob S

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #37 on: December 04, 2017, 08:25:00 AM »
Preface - I know little about 3D printing or how the various programs mentioned above work.  However, it seems to me - one issue no one is mentioning here is how the object was first created.

Recent version of Designcad has the option to "use surface representation for solid operations"  which was probably added to help create more leakproof exportable solids.

So if the object was created prior to or without using this option, or there are many other ways in which incomplete solids can be created in Designcad, then of course the finished object may be more troublesome to export.

If not, it might be interesting to recreate a few of the more complex shapes from scratch in latest version using this option, and see if that solves some of the problems
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Dr PR

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #38 on: December 04, 2017, 09:45:57 AM »
One way to create leak free solids in DesignCAD - with traditional Solids or Solid Surfaces - is to generate the solid just as you would do in the real world with a lathe or milling machine.

Start with a large solid that is big enough to contain the part you want to make. This is your "work solid."

Cut away pieces with Solid Subtract. Produce leakless "tool" solids that represent volumes you want to remove from the work solid.

Subtract the tool solids from the work solid.

You do have to learn to think the problem through in a different wy, but if you have ever used a milling machine the process should be pretty familiar.

You may end up with internal surfaces - the Solid Subtract function is not perfect. But the process cannot produce leaks in the work solid. The offset Solid Subtract described earlier will remove internal and duplicate surfaces.

This can still produce facets with more than three sides with normal Solids.

****

DesignCAD History

I suspect the original four sided polygon method of rendering surfaces dates back to pre-computer attempts to represent irregular surfaces in drafting. The idea was to drape a "fishnet" over the surface. Many early computer programs did this. They looked good on paper - or the screen - but you cannot create a true 3D curved surface with four sided polygons. There will be gaps between edges. Buckminster Fuller figured this out long before electronic computers came along - geodesic domes and buckyballs.

The original programmers of 3D DesignCAD used a simple cheat when they created traditional Solids. They bent the four point poplygons, moving one point out of the plane, to close the gaps. This essentially split the four sided polygon into two virtual triangles, although they are still drawn as traditional four-sided fishnet patterns.

But these warped polygons drove the rendering routines crazy because each facet had more than one surface normal. And the solid Boolean functions of the early 3D DesignCAD almost never worked correctly, often producing incomplete triangular facets with greatly misplaced points. It was a mess!

Somewhere along the line this internal triangle representation of grid facets was actually implemented. You can see this by finding the intersection of a plane with a grid surface. Select the intersection line in Point Select Mode and you will see the intermediate points between the sides of the polygons where the intersecting plane cut the hypotenuses of the two triangles that make up each facet. The program started doing this before V15.

I have attached an image made from a screen capture from V15 showing the intersect line (magenta) where the blue plane intersected the red grid. The intermediate points on the hypotenuses of the triangles are marked with black arrows.

Note: I drew the green hypotenuse lines manually for some of the polygons to illustrate how the four sided polygons are actually composed of two triangles.

The release date of V15 that I used was 11-Jun-04, so DesignCAD has been using internal triangle representations for grid polygons for at least 13 years. However, whenever possible it does combine multiple coplanar polygons into one many sided polygon.

The reason for this is pretty easy to understand. Many polygons create larger files than one single polygon. And in the early days of DesignCAD personal computers typically had no more than a megabyte of RAM. A simple 3D drawing can be much larger than that. The programmers did everything they could to reduce file size.

The DesignCAD "grid" surface is an example. It is a "shorthand" way to represent a lot of polygons with a simple array where each point represents the corner of multiple polygons. Create a file with a single grid, save it and note the file size. Then explode the grid ans save the file under a new name. Now compare the sizes of the two files. The exploded grid is MUCH larger than the original.

That is why DesignCAD works the way it does - to meet practical requirements of computers in the 1990s. There is a lot of legacy code in the latest versions of DesignCAD.

****

Of course today RAM isn't much of a problem. Few people (maybe only me) are crazy enough to create gigabyte DesignCAD files even though we may have machines with 32 or 64 gigabytes of RAM. Even when working on my largest files I don't use 1/10 of the RAM in my machine. Time, however, is another problem. It takes hours to render a gigabyte file.

All of this is just to explain the origins of the problems that are causing screwed up 3D STL file outputs. The only way to solve them is to work with the triangulated facets of Solid Surfaces and be very careful how you draw things.

Phil
DesignCAD user since 1987

BlankMan

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #39 on: December 04, 2017, 09:51:12 AM »
Thanks for the idea Rob. Surface verses solid representation has been mentioned in this thread and has been tried with Kevan's guidance months, maybe even a year before with DC3 MAX 2016, way before this thread was started. It does not help. I even still try it occasionally anyway and did on both objects that are depicted in this thread. It did not change the outcome, i.e. creating bad OBJ and STL exports.

You can create an object in solid representation from scratch, you can create an object in surface representation from scratch, you can convert an object that is in solid representation to surface representation. All those methods have been and are still  tried as I mentioned before, ad nauseam, and do not help.

You're welcome to try with these objects, the more eyes on a problem the better. You might find something that was missed.

I myself never give up and that is part of the reason I try things that have been tried before 'cuz ya just never know...
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Lar

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #40 on: December 04, 2017, 09:58:39 AM »

quote author=BlankMan link=topic=7007.msg50326#msg50326 date=1512402389
A rogue line connection to nothing.

That's a display ambiguity, where a part of an edge is so close to the surface covering it that the display algorithm decides to show that part. The rest of the edge is far enough away so it doesn't show.
quote author=BlankMan link=topic=7007.msg50326#msg50326 date=1512402389
Sorry but the fact that you reduce your mesh and can tell me the points edges and polygons has no real value addressing the subject at hand which is DC3 having problems triangulating.
...
Again that does not matter to viewing apps because they smooth the surfaces to make it look nice for you.
The mesh wasn't reduce to make it look prettier. The reduction happened because there were surface segments that all met at a single location so should be all sharing one point, but there were maybe 2 or 3 points there, meaning the surfaces were touching but disconnected. This is the way dcad's legacy Solids are made, with individual planes and grids touching each other. Cinema 4D wants each connection in a mesh to have only one point and each bend to be one edge. Each surface is only described by which points it uses. Eg, take a 3d cube primitive. In dcad that would consist of 2 planes with 5 points and 4 edges each, and a grid with 10 points and 13 edges, totaling 20 points and 21 edges (I'm doing this in my head so I may be off a bit). In C4D that cube would have a total of 8 points and 12 edges. Lets say the top points are numbered 1 thru 4 and the bottom are 5 thru 8, counter-clockwise. So, of the 6 surfaces, the top will use points 1, 2, 3 and 4 and the bottom will use 5, 6, 7 and 8. Now, the front will use 1, 2, 6 and 5. The right will use 2, 3, 7 and 6. Rear - 3, 4, 8 and 7, Left - 4, 1, 8 and 7. This is know as a point cloud system and this is how dcad's Solid Surfaces are supposed to work.

In my previous post when I reported how many points, edges and polygons were reduced,  what I was demonstrating was that the mesh was no longer a dcad mesh but a C4D mesh. I then exported from C4D and that is the file you opened in your software. Not a dcad export but a c4d export, so you can't put all the blame on dcad.

Either way, bottom line is I really can't help you any further unless I try your software for myself. However, seeing the issues you are having I hope when I move to 3d printing I find something more compatible, with c4d at least


Lar
« Last Edit: December 04, 2017, 10:08:56 AM by Lar »

BlankMan

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #41 on: December 04, 2017, 10:31:57 AM »
Phil I can give you an example of when a rectangle was created with the Box command and a hole was drilled centered through the rectangle with a Cylinder and that rectangle went south at the time Cylinder was SolidSubtract'd from the Box.

I already do what you're saying to some extent. Since the Fillet* commands have problems too that cause problems I'll create a plane with arc for the fillet I want then extrude or sweep it and subtract that from where I want the fillet.

Since I have my own milling machine and lathe I have to think all the time in the way you mention because I'm taking a chunk of metal and making it into what I want.

And Phil, thanks for the history! I appreciate you taking the time to write that. I found it very interesting and am always interested in stuff like that. I've been in IT approaching 40 years now, I know exactly what you're talking about. To date myself I wrote device drivers in assembly language for S-100 systems and it didn't stop there. I continue to contribute to the Open Source world and even have packages in Linux distributions.
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BlankMan

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #42 on: December 04, 2017, 10:51:40 AM »
Lar I never said you do the mesh reduction to make things prettier what I said is that you don't always see the results of mesh reduction i.e. facet reduction in 3D viewers because they tend to do surface smoothing.

And Lar, Simplify3D and Cura are two of the top and highly used 3D printing slicers, and I believe Cura is free. You find one that has all the features of these two that can take DC3's poorly generated OBJ and STL files (before DC3 is improved so it doesn't happen any more) and can properly slice and print these files please do let me know.

Because until DC3 fixes it's triangulation algorithm it's going to continue to occur with DC3's OBJ and STL exports. If it were caused by something I'm doing or not doing, in the 2+ years this has been going on I'm sure Kevan or someone at IMSI would have told me how to fix it. 
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Lar

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #43 on: December 04, 2017, 11:50:30 AM »


BM, I downloaded Cura and loaded your SpaceBar in OBJ and STL with no problem (Well, at first nothing loaded but reading the manual explained that a 3d printer must be added first, which I had skipped when the app first opened. I jus picked the first on the list). Came across very tiny though. I'll figure that part out later.

See attached image. I rotated the models to get a good view, since I can't figure out how to rotate the view. Not sure what the red is on the STL. Maybe the reversed surfaces.

But like you said somewhere, it may load ok but who knows if it will print ok.


Still, at least it doesn't look messed up like in your images.


Lar
ps: I just attached a second image with the most left (and tilted)Spacebar being an STL coming directly from dcad. I only tilted it to see the inside better. Notice it has very few red areas (whatever that means). The back is perfect and has no red at all.
« Last Edit: December 04, 2017, 12:23:41 PM by Lar »

BlankMan

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Re: Does anybody here export STL or OBJ format for 3D printing?
« Reply #44 on: December 04, 2017, 01:34:48 PM »
Wow Lar, now you got me thinking, thanks for taking the time and trying this.

Maybe Cura is more forgiving then Simplify3D, i.e. can fix things S3D can't.

I'm going to have to do some experimenting and see if I can import problematic exports into Cura, let it do it's magic, then export it as an STL and import it into Simplify3D. I lean towards still using S3D for slicing because it has an edge on Cura in for one thing support structures but not only for just that reason.

Once you get into 3D printing you'll see why. My two objects in this thread aren't examples of when support structures are essential.

And if that is the case, Cura can, S3D can't, my next stop will be showing that to S3D Support and ask why?

This is why I started this thread here, thanks Lar! Thanks all! But don't assume this is over, never know...   :)  :) :)
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