<p>I'd like to customize and modify some parts on Thingiverse, beyond just simple scaling for 3D printing.</p>

<p>I've been looking for some tools that convert the STL files into something that is easily edited, but so far all that I've found are really buggy and crash frequently as soon as one loads a reasonably complex model.</p>

<p>Are there any free open source software tools that people can recommend that handle STL importing and editing? If not FOSS, what about just "free or nearly free for hobbyists, ed, non-commercial?</p>

[{'answer_id': 448, 'author': 'Leo Ervin', 'author_id': 381, 'author_profile': 'https://3dprinting.stackexchange.com/users/381', 'pm_score': 2, 'selected': False, 'text': '<p>There is no argument that the most successful FOSS 3D editor is Blender. It can both import and export STL files and export to STL or many other formats (DAE, OBJ, 3DS, FBX, DXF, WRL) so you can both use it to edit STL models as well as just use it as a STL converter.\n<a href="https://www.blender.org/" rel="nofollow">https://www.blender.org/</a></p>\n'}, {'answer_id': 453, 'author': 'Tormod Haugene', 'author_id': 115, 'author_profile': 'https://3dprinting.stackexchange.com/users/115', 'pm_score': 3, 'selected': False, 'text': '<p>If you want to do basic edits to an STL, a program such as <a href="http://www.meshmixer.com/" rel="noreferrer">MeshMixer</a> might be right for your. It offers the ability to combine and subtract models, add custom supports, and similar, in a fairly straight forward manner.</p>\n\n<p>An alternative that allows your to do complex editing of STLs would be <a href="http://www.autodesk.com/products/fusion-360/overview" rel="noreferrer">Autodesk Fusion 360</a>. Here you can import STLs into meshes, which you then may convert into solids for further editing. It is more work to use, but a very flexible solution; you can i.e choose to only convert certain faces to solid, or use the mesh as a reference point for other designs. </p>\n\n<p>As far as I know, neither of these are FOSS (free and open source),  but both are free for non-commercial use.</p>\n'}, {'answer_id': 587, 'author': 'tourdetour', 'author_id': 585, 'author_profile': 'https://3dprinting.stackexchange.com/users/585', 'pm_score': 3, 'selected': False, 'text': '<p>You can use <a href="http://www.openscad.org/">OpenSCAD</a>. It\'s a script based powerful CAD open source software under GPL. \nOn Thingiverse, a <a href="http://www.thingiverse.com/search/prolific/things?q=&amp;search_mode=advanced&amp;description=&amp;username=&amp;tags=Customizer&amp;license=">lot of things are</a> made with this CAD software (the <code>Customizer</code> flagged ones) and you can just download their source code (<code>.scad</code>) and directly edit them !</p>\n\n<p>You can also import existing STL and edit them like they were a primitive shape like a cube. You can then interact with them by doing binary operations, adding parts, etc. </p>\n\n<p>It is hard to start with if you have never coded, but that\'s worth it :</p>\n\n<blockquote>\n  <p>OpenSCAD is a software for creating solid 3D CAD models. It is free software and available for Linux/UNIX, Windows and Mac OS X. Unlike most free software for creating 3D models (such as Blender) it does not focus on the artistic aspects of 3D modelling but instead on the CAD aspects. Thus it might be the application you are looking for when you are planning to create 3D models of machine parts but pretty sure is not what you are looking for when you are more interested in creating computer-animated movies.</p>\n</blockquote>\n'}, {'answer_id': 602, 'author': 'BYE', 'author_id': 442, 'author_profile': 'https://3dprinting.stackexchange.com/users/442', 'pm_score': 2, 'selected': False, 'text': '<p>I have used Wings 3D (<a href="http://www.wings3d.com" rel="nofollow">http://www.wings3d.com</a>) for just that purpose. It is very easy to use, and has many other useful functions built in. Not only can you reform the mesh, but you also you have the ability to import and export many other meshes such as .obj, and etc. When you have completed your modifications you can export them in one of several formats (I find it easier to just keep it in .stl) and then use netfab (also has a free version with some limitations as compared to the paid version) to fine tune the mesh if it is not printable in its current format. Wings will export your modifications in .stl format, but you may have to fine tune to get rid of holes blemishes and etc., and you can view your changes in several views such as Gaussian and other forms. </p>\n\n<p>If you decide to try Wings 3D you need to go through the tutorials, since there is a multitude of possibilities, including making your own meshes, beginning with several basic forms such as squares, cubes, cylinders and several other basic geometrical figures.</p>\n\n<p>Using these two programs I have been able to modify many meshes and arrive at a very printable object. One of the features of Wings which has been quite valuable is the smoothing app which reduces the sharp division lines on some models.</p>\n\n<p>Since both programs are free you can try them and uninstall them if they do not fill your needs. Blender is also an excellent free program, but I find Wings to be much simpler to use.</p>\n\n<p>Hope this helps   </p>\n'}, {'answer_id': 608, 'author': 'ahulpke', 'author_id': 39, 'author_profile': 'https://3dprinting.stackexchange.com/users/39', 'pm_score': 0, 'selected': False, 'text': '<p>If you want a WYSIWYG-style editor and are not content with OpenSCAD, I found 123D Design (Autodesk, definitively not FOSS but free for hobbyists) to have (on a Mac) a compromise between power and ease of use that most appealed to me.</p>\n\n<p>If you insist on FOSS probably Blender comes closest, but I found it to be too idiosyncratic in interface and tools to be usable. </p>\n'}]
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