STL files are most commonly used to make 3D models, ahead of OBJ files, by the vast majority of the 3D printing community.

Once the STL of the desired model has been selected, it must be entered in a rolling software (Cura, Simplify3D...) to generate the GCode, code used by the 3D printer for manufacturing. In this software the user can vary all the parameters of impression and must verify the model looking for open zones between faces or surfaces, since if they exist, they will cause errors in the form of voids or filament detachments by the piece..

Many times we are limited when designing complex models, but thanks to the existence of repositories of 3D models can be found these already designed. You can find all kinds of designs, from basic things like a coaster, to complex things like cars or artistic figures of great complexity.

Here are 5 of the best-known free repositories of 3D models available:

Thingiverse

Pertaining to the famous brand of printers 3D MakerBot, Thingiverse is the web with more STL files available and with greater number of downloads. In it you can find all kinds of 3D models accompanied by the parameters of printing, material used, finishing processes and even explanatory videos. Another point to emphasize is the ease with which the desired design can be searched, both in the search engine for words and categories: art, fashion, gadgets, hobby, home, models, tools and games / toys.

Cults

Cults is a very well structured page with all its classified content and with the possibility to sort it by price, date, downloads and likes. Prices vary depending on the complexity of the models, although there are many that are free or cost very little. Most of the available files contain information about the print parameters and are tested by the makers to ensure the viability of 3D printing. In this platform also users can sell and buy 3D models, apart from requesting the design of their ideas depending on the budget they have.

GrabCAD

This web was born for the eagerness of the community of engineers to share their models for free. Today there are almost 4,000,000 members with 2,240,000 files. These models are not only in STL format, but in many other more CAD world (AutoCAD, Autodesk, CATIA, Onshape, SOLIDWORKS, STEP / IGS and many more). It can be found from screw models, to designs of real life cars and always free download.

MyMiniFactory

It has 30,000 designs and more than 5,000 designers. All available designs are carefully selected and tested to ensure 3D printing without errors or problems due to the STL file. All available models are free and if needed, you can request the design of a piece for the MyMiniFactory community, which will then be shared on the website.

Yeggi

Yeggi isn't like previous webpages in which the community share their 3D designs, but it is the largest search engine for STL files on the web for 3D printing. In Yeggi you can find any design of the main STL file repositories, which is why it is currently the largest comparator. If you need a particular model, you are probably here. At an older age, it is very useful to know the popular searches of the moment and to be updated in the trend of designs and 3D impressions of the community.

 Use licenses

Downloading of STL files is usually regulated by some use licenses. For example, Thingiverse is regulated by Creative Commons licenses, a non-profit organization that offers a set of legal instruments that makes it easier to use and share all kinds of knowledge. The different licenses that can be found in Thingiverse are:

1. Attribution (CC-BY): All types of use (including commercial) and modification of the work are allowed.

2. Attribution Share Alike (CC-BY-SA): Any work under this license may be modified, even for commercial purposes by citing the original author and maintaining the license used by the latter.

3. Attribution Non-Commercial (CC-BY-NC): You can't market the work but you can generate works derived from the original.

4. Attribution Non-Commercial Share Alike (CC-BY-NC-SA): Commercial use isn't permitted but if the work is modified as long as the authorship is recognized and new creations are under a license with the same terms as the original.

5. Attribution NoDerivatives (CC-BY-ND): It can be commercialized without modifications in the work and with recognition of its authorship.

6. Atribution Non-Commercial No Derivatives (CC-BY-NC-ND): It's the most restrictive license, it doesn't allow any type of modification or commercial use, only the download is accepted and shared with other people recognizing the author.

Apart from the 5 download sites mentioned above, there're many more that are also interesting like: 3Dagogo, Instructables, Pinshape, Autodesk 123D, YouMagine, Bld3r, Shapeways...in which you can find all kinds of designs that a person can imagine.

So today, not knowing how to design in 3D is no longer a totally limiting factor thanks to these online repositories of STL files.