Smooth Print Polygon Question

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Smooth Print Polygon Question

Postby arcadiax » 2016-Apr-Mon-22-Apr

Hello everyone,

I am new to the forum and have a question about 3d Printing with Repetier and Printrbot Simple.

I have tried printing a simple vase, and inside 3D studio max, the walls are all very smooth because I would auto smooth everything. However when I try to print it out, it looks somewhat polygonal? Look like a somewhat low-polygonal vase with semi-flat sides, not the very smooth-roundish sides.

The walls look like facades, not the very smooth feel.

Is this perhaps a setting in Repetier?

Thank you for reading my thread, any help is deeply appreciated.
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Re: Smooth Print Polygon Question

Postby RetireeJay » 2016-Apr-Tue-07-Apr

I suggest you start by looking at your settings in 3D Studio Max when it exports the model in STL format. STL files don't actually create curved surfaces; they represent the surface of the object as a number of flat triangular tiles. If the number of flat tiles is very large, it will create a smooth representation that will appear curved; but if the number of tiles is too small you will easily see the faces and edges of the tiles. In my CAD software, there is a setting for the minimum number of degrees of angular difference between faces that will lead to the creation of new tiles in the STL output. I have found that 5 degrees creates round parts that have barely-perceptible flat faces.
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Re: Smooth Print Polygon Question

Postby arcadiax » 2016-Apr-Tue-13-Apr

Jay, thank you very much for your prompt reply. I will give that a try and keep you posted!
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Re: Smooth Print Polygon Question

Postby arcadiax » 2016-Apr-Tue-17-Apr

Hi Jay,

I tried to look in 3D Studio Max if there were any options for tweaking the export .stl file, but it seems 3D studio Max exports .stl in a rather simple process.

1. Export.

2. Have a choice of either Binary or ASCII. No additional parameters or roll down windows, etc.

For CAD, is it much more robust in terms of .stl exportation options? I do not have CAD software so I am just curious. I might need to get it I suppose...
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Re: Smooth Print Polygon Question

Postby musk » 2016-Apr-Tue-17-Apr

3dsMax is (primarily) a polygonal modeling tool, not a parametric CAD tool like Solidworks or Inventor. 3dsMax creates objects directly as polygon models. If your model looks polygonal in Max, it will be polygonal when printed. You *must* change viewport settings to display in "Facets" mode to see the polygons. Anything else will lead you astray by making geometry appear different than it really is.

CAD programs create infinite resolution models which are only converted to polygons when exported to .stl as a final step. In that case, default export settings usually give a very smooth and poly-heavy result as there's not much point in exporting a low-detail model from cad.
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Re: Smooth Print Polygon Question

Postby RetireeJay » 2016-Apr-Tue-19-Apr

arcadiax wrote:For CAD, is it much more robust in terms of .stl exportation options? I do not have CAD software so I am just curious. I might need to get it I suppose...


CAD stands for "Computer Aided Design" - which is these days just a legacy generic name (originally, it was helping / replacing pencil-and-paper drawings like the kind of drawings that became blueprints). Today's CAD systems are much more than replacements for drawings on paper.

Technically, your 3D Studio Max could be called a CAD program. There are many programs available, ranging from free to commercial ones only affordable to corporations. There are several free or inexpensive ones reviewed in this forum. viewforum.php?f=26
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Re: Smooth Print Polygon Question

Postby cacb » 2016-Apr-Wed-04-Apr

musk wrote:CAD programs create infinite resolution models which are only converted to polygons when exported to .stl as a final step. In that case, default export settings usually give a very smooth and poly-heavy result as there's not much point in exporting a low-detail model from cad.


This is not quite the full picture.

As you say, Some CAD programs, notably the traditional ones, use an internal complex geometric/topological representation based on lines, splines, circular arcs. etc. FreeCAD is one such example as it is based on OpenCasCade, there are many other commercial equivalents like this. The discretization to polygons happen on export to STL, where the polygons are always triangular.

However,several other CAD programs, like OpenSCAD, use an internal polyhedron representation where essentially the surface of any solid is described by flat polygons. You can typically request a high discretization and obtain very close approximations to the original smooth geometry. The boolean operations here work on polyhedrons, so the discretization happens at an earlier stage. You will find that some people actually (mis)use the early discretization to get certain effects. an example from OpenSCAD : cylinder(r1=10,r2=0,h=10, $fn=4);

You would think this would generate a cylinder, but what you really get is the great pyramid of Giza :-)
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Re: Smooth Print Polygon Question

Postby Mooselake » 2016-Apr-Wed-15-Apr

cacb wrote:You will find that some people actually (mis)use the early discretization to get certain effects. an example from OpenSCAD : cylinder(r1=10,r2=0,h=10, $fn=4);

You would think this would generate a cylinder, but what you really get is the great pyramid of Giza :-)

If the Egyptians only had OpenSCAD...

I'd call it creativity rather than misuse. I did a couple facepalms when I discovered cylinder(r=10 h=2, $fn=6) was the easy to way to make a nut trap (for machine screw nuts, not what you first thought of...).

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Re: Smooth Print Polygon Question

Postby musk » 2016-Apr-Wed-16-Apr

cacb wrote:
musk wrote:CAD programs create infinite resolution models which are only converted to polygons when exported to .stl as a final step. In that case, default export settings usually give a very smooth and poly-heavy result as there's not much point in exporting a low-detail model from cad.


This is not quite the full picture.

As you say, Some CAD programs, notably the traditional ones, use an internal complex geometric/topological representation based on lines, splines, circular arcs. etc. FreeCAD is one such example as it is based on OpenCasCade, there are many other commercial equivalents like this. The discretization to polygons happen on export to STL, where the polygons are always triangular.

However,several other CAD programs, like OpenSCAD, use an internal polyhedron representation where essentially the surface of any solid is described by flat polygons. You can typically request a high discretization and obtain very close approximations to the original smooth geometry. The boolean operations here work on polyhedrons, so the discretization happens at an earlier stage. You will find that some people actually (mis)use the early discretization to get certain effects. an example from OpenSCAD : cylinder(r1=10,r2=0,h=10, $fn=4);

You would think this would generate a cylinder, but what you really get is the great pyramid of Giza :-)


Sure, and you could also model with NURBS inside 3dsMax if you want infinite resolution. Typically though, people generate polygonal models in Max or Maya and create parametric solids in Inventor or Solidworks.
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Re: Smooth Print Polygon Question

Postby cacb » 2016-Apr-Thu-14-Apr

Mooselake wrote:I'd call it creativity rather than misuse. I did a couple facepalms when I discovered cylinder(r=10 h=2, $fn=6) was the easy to way to make a nut trap (for machine screw nuts, not what you first thought of...).

I know. I just don't want to rely on an effect that might go away one day. And I want a cylinder to be a cylinder, but perhaps that's just me :?
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Re: Smooth Print Polygon Question

Postby arcadiax » 2016-Apr-Sat-01-Apr

Hey guys, great replies and insights. I appreciate the feedbacks and knowledges. I especially like the part Musk mentioned about changing the viewport mode to Facets. That helped greatly.

My background actually started out as an 3D animator and modeller and leaping into the reality side of this whole thing has been many ups and downs. Technology was never my forte.

This part is a little off topic, but soon I am planning to order a Desktop CNC Kit from Zen CNC. Hopefully everything goes well with that thing in the end. Entering the realm of techies / hobbyist engineering and electronics is still quite a daunting and intimidating step for me - mechanically non-inclined type here :). If I can even get past the techies part, forget about the whole engineering and electronics aspect lol...
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Re: Smooth Print Polygon Question

Postby thawkins » 2016-Apr-Sat-09-Apr

arcadiax wrote:Hey guys, great replies and insights. I appreciate the feedbacks and knowledges. I especially like the part Musk mentioned about changing the viewport mode to Facets. That helped greatly.

My background actually started out as an 3D animator and modeller and leaping into the reality side of this whole thing has been many ups and downs. Technology was never my forte.

This part is a little off topic, but soon I am planning to order a Desktop CNC Kit from Zen CNC. Hopefully everything goes well with that thing in the end. Entering the realm of techies / hobbyist engineering and electronics is still quite a daunting and intimidating step for me - mechanically non-inclined type here :). If I can even get past the techies part, forget about the whole engineering and electronics aspect lol...


Just a quick observation on the ZEN, I have one. You have to temper your expectations, the device is made out of HDPE plastic, and is not very rigid, because of that it can't mill hard materials like aluminium or brass. It's pretty much limited to woods and acrylics etc.
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