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Thread: Need advice on Modelling for 3D printing

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    Need advice on Modelling for 3D printing

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    Hi there! I'm a beginner on Lightwave and I'm trying to create some game coins for 3D printing. But the process ended up with lots of bad polygons the printer can't understand.

    I rushed it and used a 2nd party modelling software to combine the numbers from Lightwave. The cylinder was made in Silo 3D.

    I want to create a new coin solely in Lightwave now but how can I avoid making more bad polygons when I combine the numbers on to the cylinder? This coin is supposed to be two-sided.

  2. #2
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    Merge Points, then Unify Polys.
    Check whether you have 1-2 point polygons, and delete.
    Press + in Polygon Statistics and hit delete.

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    Super Member spherical's Avatar
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    I assume by "combine" you are using Boolean operations with two models. The issue with that is that, if the meshes are dense enough, there will inevitably be situations where the positioning of the two models will cause a bad condition, as far as the Boolean function is concerned. The more dense the mesh, the higher probability of this occurring. These two models are triangulated and appear to not be one mesh at this stage. Doing Bool Ops with Quads lessens the probability of a bad situation occurring, as there will be roughly 25% fewer Edges to cause problems, as you'll see. Convert the Tris into Quads, if necessary, then work with it. Triangulate as a last step.

    A point is dimensionless. An Edge has only one dimension. The Point can never be divided in two. The Edge can only be divided along its one dimension; you cannot make an Edge be half its thickness—because it has no thickness. If the cutter surface encounters either of these through an axis of a Point or an Edge that has no dimension, the operation will either not cut the polygon or delete it; leaving a bunch of overhanging or missing cruft polys that have to be manually modified through Point Welding and One-Point or Two-Point poly deletion in order to make a water-tight mesh that a slicer can understand. That, or the Bool Op will fail altogether.

    In your Point Statistics panel there are :
    • Points on zero polys. They can safely be deleted, as they are not forming a surface.
    • Points on one poly. These are most likely vertices that are on polys that need to be welded to other nearby points in order for a poly to form.
    • Points on two polys. Can be some of the above or deleted if they do not add any information to the mesh shape. IOW, along an Edge that if the Point is deleted nothing changes, as it is left over from a Poly Reduction.

    Those three need to be dealt with first, along with consulting the Poly Statistics. Not having that to see, it is difficult to advise, but the usual situations are:
    • Polys having two Points. These will be left over when Polys are deleted or reduced. Pretty much, depending upon the Point conditions, above, they can be deleted. Check before doing so.
    • Polys having three points. Here's where working in Quads has another benefit. Three-point Polys are all that should be in a Triangulated mesh. Polys having three points in a Quad mesh are ones that need attention. This makes identifying the problem areas easier. Sometimes, you have to add a Point to an Edge, either with "Add Points" on a selected poly or "Connect" on a selected Edge, in order to be able to weld it to a nearby vertex and close a hole.
    • Polys having more than four points can exist as N-Gons in a predominantly Quad mesh, but a Triangulated mesh should not have any. Use "Connect" to create an Edge between two selected Points until you get to all Quads or Tris. OR, you can just wait for the Triangulation Op later.

    Also check Edges Statistics. In all cases, there should be Edges on two polys. No more, no less. They're Edges that have no dimension, other than length, that join two things that have two dimensions:
    • An Edge on one poly, will show as a 2-point Poly in the Poly Statistics or be on a Poly that has a Point on only one poly or be on an N-Gon poly that has a drilled hole like the "0". The latter is the only situation where an Edge on one poly is legal.
    • An Edge on more than two polys will likely be a sign of interior geometry, polys within the actual outer surface of the model, or will be a redundant poly that is 2-point.

    In any case, always Merge Points after a Bool Op choosing Automatic first, unchecking Keep 1-Point Polygons. If I have a problem mesh, I'll then re-run Merge using Fixed, starting with a very small value depending upon the mesh density, to weld very nearby points that Automatic ignored. Check with a zoomed in view to see if the mesh is degraded too much and Undo back to an acceptable value of Point distance, then commence the manual fixing Op from there on.

    Once that is all done, you should have a clean, water-tight model that is ready for Triangulation. Then all polys will have three points and most all points will be on three polys; with the exception of conditions where many Tris are joined by one Point, as in the situation of a pole of a sphere.

    Slicers need models that are "Manifold"; having only one outside and one inside, with nothing inside. If there are intersecting, overlying, overlapping or missing polys, the slicer cannot correctly analyze and identify the surface and cut it up into layers to create a tool path that will reassemble the shape.

    In a situation like this, however, I would suggest not doing a Bool Op with two models but create the number's outline on the coin with "Drill" or "Solid Drill" using "Stencil" or "Slice" mode. This will make new Edges on the coin surface that you then Smooth Shift their interior polys up. Far easier to repair any anomalies and extraneous geometry when it is 2D, then make it 3D. In order to get the domed upper surface of the letters onto the shifted stencil, which will have the contour of the coin, cut the top polys of the Smooth Shifted number and paste the top polys from the number model, then Merge Points.

    Note that this all applies to LightWave's native Boolean tool. Various commercial plugins, like 3rd Powers Boolean Tool in LightWave and Mesh Fusion in Modo, can better handle Ops like these, creating geometry at surface intersections where needed; even with filleting.

    I had a high density model that is 4 feet long, having points roughly 0.060" pitch distance on average, that I had to cut along its length to create top and bottom halves. What made it even more difficult was that it was a tapered compound curve that undulated in all three axes; much like a curved tentacle in a "?" shape. 4" x 6" oval cross section at the root, morphing and tapering to round at mid distance and tapering to a point at the tip. The Bool Op left a LOT of cruft along the cut edges that had to be fixed before using Thicken to create a hollow shape that would be printed to be used as molds into which carbon fiber would be formed. It took a LOOOONG time to go through a mesh that dense and locate all problem areas before going to the next step. Save early. Save often.
    Last edited by spherical; 05-22-2015 at 07:21 PM.
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    Thanks for the tips. I was hoping to start over with a flat circle polygon. I need the practice with Lightwave's tools.

    Then somehow I'd combine it with the initial flat text of '10' with the text tool.

    From there I thought I'd extrude select areas to form the rim and the numbers. They don't need to have the same depth from the surface.

    Then I'd extrude the outmost sides back down for some depth and mirror it to create a two-sided coin. Once it's a whole object I'd fix any n-gons. Does that sound feasible?
    Last edited by Bernie2Strokes; 05-22-2015 at 10:45 PM.

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    Super Member spherical's Avatar
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    Well, you certainly can start over using a different approach. It may yield better or equal results, and you'd learn the benefits/pitfalls of them, but I was attempting to offer a solution to the existing method.
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    I'll try that out too. Thanks.

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    Coin Progress

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    Okay. So I've started over because the first model was too busy for me keep track of extra points and polygons.

    I drilled the flat polygon of the no. 1 on to the surface of a new cylinder. I looked up the Drill command options and it drew the shape in better than trying a Boolean operation.

    First I extruding it with Extender Plus and pressing 'T". But I couldn't repeat the same results so I just used the normal Extrude command.

    Instead of using the Mirror command I tried Clone and merged the overlapping points.

    I think at this stage I should cut up the geometry around the number 1 before I eliminate the junk points and polygons.

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    For many printers (and you should check the one you are using), there is no need for the number and the coin to be on single object. As long as the number object intersects the coin object, you'll be ok. You just need to make sure that all of the polygons are 3 or 4 points. A simple triple of polygons >4 points should work on an object this uncomplicated. (Unless you plan to subdivide it, in which case you need to try to put better geometry in. But, the thing that will simply this process more than anything is not having the numbers be part of the coin. (all of this is based on the assumption you want the numbers extruded from the coin, rather than embossed into it.)

  10. #10
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    I don't know how to fix the number 'zero' in Lightwave. It's filling up the inside space instead of being an oval with a gap inside.

    Before I just exported the number '10' into Silo 3D and played with it there. But I want to now how to fix problems like this in Lightwave itself.
    Last edited by Bernie2Strokes; 05-25-2015 at 03:22 AM.

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    Quote Originally Posted by gordonrobb View Post
    For many printers (and you should check the one you are using), there is no need for the number and the coin to be on single object. As long as the number object intersects the coin object, you'll be ok. You just need to make sure that all of the polygons are 3 or 4 points. A simple triple of polygons >4 points should work on an object this uncomplicated. (Unless you plan to subdivide it, in which case you need to try to put better geometry in. But, the thing that will simply this process more than anything is not having the numbers be part of the coin. (all of this is based on the assumption you want the numbers extruded from the coin, rather than embossed into it.)
    I saw that mentioned in a video. I don't know if I should try that because I need to make a whole set of coins of each value. I still don't if I should lay them out in Lightwave with an array or just duplicate them manually in the printer's own software.

  12. #12
    Super Member spherical's Avatar
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    Quote Originally Posted by gordonrobb View Post
    For many printers (and you should check the one you are using), there is no need for the number and the coin to be on single object.
    Slight correction. It's the slicer, not the printer. Printers know only that which the slicer sends them; that being a G-Code file that a slicer generates. If a slicer understands multiple meshes (also called sub-meshes) then, yes, the two shapes do not have to be combined into one before slicing.

    Even if a particular printer has a companion software that may or may not be specific/proprietary, it's still a slicer. It could be a Cartesian or a Delta printer or a laser. Makes no difference when you get down to it. The process is still essentially the same and many slicers that are not associated with any printer will be able to work with all of them.
    Last edited by spherical; 05-25-2015 at 03:51 AM.
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  13. #13
    Super Member spherical's Avatar
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    Quote Originally Posted by Bernie2Strokes View Post
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    Okay. So I've started over because the first model was too busy for me keep track of extra points and polygons.

    I drilled the flat polygon of the no. 1 on to the surface of a new cylinder. I looked up the Drill command options and it drew the shape in better than trying a Boolean operation.

    First I extruding it with Extender Plus and pressing 'T". But I couldn't repeat the same results so I just used the normal Extrude command.

    Instead of using the Mirror command I tried Clone and merged the overlapping points.

    I think at this stage I should cut up the geometry around the number 1 before I eliminate the junk points and polygons.
    I'm not really grokking what you are trying to do, here. If you Drill the surface and get the outline of the number on it, select the number's polys and Smooth Shift.

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    This is a single poly with a hole in the middle, emulating your "0" number character. Drilled into the top poly of the box using Stencil mode. Select the poly that forms the "0" and Smooth Shift it up.
    Last edited by spherical; 05-25-2015 at 04:08 AM.
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    Quote Originally Posted by spherical View Post
    I'm not really grokking what you are trying to do, here. If you Drill the surface and get the outline of the number on it, select the number's polys and Smooth Shift.

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    This is a single poly with a hole in the middle, emulating your "0" number character. Drilled into the top poly of the box using Stencil mode. Select the poly that forms the "0" and Smooth Shift it up.
    I forgot to mention that I'm doing three different coins here. They have values of 1,5, & 10.

    I followed an online video on using the Drill command and it used both Extender Plus followed by pressing 'T'. It also used Extrude. I don't see how the results are different from Smooth shift

    Anyway, I'll try drilling a stencil into the number '0'.

  15. #15
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    Quote Originally Posted by Bernie2Strokes View Post
    Anyway, I'll try drilling a stencil into the number '0'.
    You're not "drilling a stencil into the number "0", you're drilling the "0" into the coin.

    The "1", "5" and "10" are essentially irrelevant. You can use the text tool to create the numbers or import a font through EPS to get a poly that is shaped like the number you want. Use that poly to Drill.
    Last edited by spherical; 05-25-2015 at 04:19 AM.
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