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Thread: converting .stl mesh file to .3dm?????

  1. #1

    converting .stl mesh file to .3dm?????

    I have one customer needing some complex parts based on an existing part. The last time I did this I paid through the nose to get the part laser scanned. The file I received was a .stl file that was in a word HUGE. I loaded into Rhino and needed to plug one hole and insert another. This was not easy and was very slow not to mention crashing my computer.

    Is there a way to convert a .stl mesh to a file that can be converted into a
    .3dm file so that I can edit the part in a reasonable way. I tried saving the mesh as a 3dm but it was just saving it as a bunch of triangular surfaces.

    I haven't a clue how to deal with this problem and would appreciate any reasonable ideas.

    Thanks

    Jack

    Similar Threads:
    Jack Mc Kie
    [URL=http//www.freshwatermodels.com]Freshwater Models[/URL]


  2. #2
    Hi,

    Unless the part fits into a special case, there's no nice automatic way of "converting" a mesh to NURBS, not without very expensive software. Re-modeling the part just using the mesh as a reference is the way to get the best NURBS result.



  3. #3
    J Curuthers,

    Thanks for your post!

    Can you give me a rough idea of how to go about using the mesh as a reference? I need to do this on a few parts a year and they usually have complex surfaces and detail that would be tough to model.


    The parts I have now are 1939 outboard cowls with organic shape and relief logos etc.

    I am going to a possible vendor tomarrow who says he can do it with a CMM and produce a dxf file????? My guess is that they can't produce all the detail so it may at least be a start with the rest being done from a photo as a bitmap background. I think this project is going to get expensive for my customer.

    Is there software that allows easier/faster editing of meshes?

    Was hoping for a simple answer but seldom is this the case.

    Thanks,

    Jack

    Jack Mc Kie
    [URL=http//www.freshwatermodels.com]Freshwater Models[/URL]


  4. #4
    Well it's mostly just a matter of bringing the mesh in and modeling the object as if you were building it from scratch. You can take sections through the mesh and draw on it, but then you have to clean those curves up.... To test your accuracy you use "PointDeviation."

    I don't think a CMM's going to help much/any over a scan, it indeed won't be able to capture all the detail and will still give you a mesh...maybe if it's cheaper just to make a start.

    Rhino Sales, Training, Consulting
    www.hydraulicdesign.net


  5. #5
    Of course I should note that if you have a good scan it should not be necessary to reverse-engineer everything, just the modified areas, which you can then turn back into meshes and integrate into the scan model. Of course I'm sure it sounds a little simpler than it is.

    Rhino Sales, Training, Consulting
    www.hydraulicdesign.net


  6. #6
    What I need to do is to is be able to change the mesh to a nurbs. Rhino as I see it is very limited in editing mesh. I need to change surface and add features. Yesterday I was told by McNeel techie that it was easy to go from nurbs to mesh but not the reverse. Thyt it is a bit sketchy to me and looks like it will be a very tedious and inaccurate method. I also see that there is at least a couple of plug-ins that are supposed to do it but they are from places I don't care to do business with.

    I'm thinking of measuring the part using a grid pattern to develope curves to loft and then add details. Customer may not want to pay for the time involved in this project.

    Jack

    Jack Mc Kie
    [URL=http//www.freshwatermodels.com]Freshwater Models[/URL]


  7. #7
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    I am having the same problems tryinig to model guitars.

    There are programs called Pointcloud,Meshcad, and TerrainCAD for Rhino http://www.sycode.com/products/point_cloud/index.htm
    This may offer some help.

    I can with the laser scanner produce dat,dxf, and stl files but all need cleaning up extensively. I really haven't found a good way to translate these into usuable data easily. Programs like Cut3d and Artcam can read these files and cut a reasonably accurate model from your original data but there is no changing or modifying such.

    Let me know if you find any.

    Kevin



  8. #8
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    We use Polyworks or Geomagic to do it. If you don't want to spend the $$$ for those software, we can do it as a service, PM me. It takes hours not days to get a good NURB out of a mesh. Mesh can come from anywhere (PC-DMIS, CMM, Romer arm, etc) and we can do the scanning too. RE is not for everyone.



  9. #9
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    Well, if at all possible, I would stay in mesh format. It is either time consuming or expensive to convert mesh to NURBS, so first investigate the possibilities of editing the existing mesh and manufacturing from that.

    You say that you need to "change surface and add features" Let's take these one at a time. Mesh editing IS limited in Rhino but you can still move control points around, making it possible to locally change the mesh. You can scale either the whole mesh or parts of it (again with control points), the various other transforms also work on meshes or mesh control points.

    Another very useful tool might be CageEdit, you can put a cage around the object or part of it and use that to edit the object.

    Now, as to "add features". You can model your new features in NURBS. When you're done, you can mesh them. The hard part is getting them integrated into the existing mesh model. You can try Rhino's mesh boolean operations or mesh trim, split, etc., but there is a good possibility they will not all work. You may be able to do some manual editing by removing parts of the mesh (delete mesh faces) and add new ones.

    The question is, do you really need to integrate the new pieces into the existing mesh part...? Some milling software won't care if you have overlapping pieces, whatever's below the outer surface doesn't matter. I know this seems sloppy, but in the world of prototyping, anything that gets you your part made faster is generally good.

    A lot of this depends on how many parts you need to make, what material, etc. If you're only making one part out of wood or plastic, for example, iy may also be faster/more reasonable to have a less than perfect computer file and make the corrections by hand on the milled part afterward (sanding, etc.).

    Anyway, just another couple of ideas... --ch

    Last edited by chmillman; 07-05-2009 at 04:42 AM. Reason: spelling/clarity


  10. #10
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    I did download a conversion utility through the Rhino3D.com website about a year ago. It was a Mesh-to-3dm converter. Check out the McNeel site for possibilties. I was called ReverseRhino. Check here:
    http://www.rhino3d.com/re.htm



  11. #11
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    I have been struggling with converting a whole car to nurbs from 3dsMax, Rhino with T-Splines has done a nice job of converting the mesh.



  12. #12
    Rich,

    Could you explain what you are doing?

    Jack

    Jack Mc Kie
    [URL=http//www.freshwatermodels.com]Freshwater Models[/URL]


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