I just found for myself mecabricks.com. Amazing! However I wonder where do they take models of their parts from? Are they all self-designed (and proprietary) or come from some open source? Is there any open library of parts ready to be imported into a 3d editor?
LDView is probably the easiest way to export parts, and it directly supports exporting POV, 3DS, and STL formats. By default the parts exported will not have smooth curves on subparts, such as studs. This may be important depending on how realistic you want you model to look in your 3D software. This can be changed in LDView by clicking on the Edit > Preferences... menu item, then clicking Primitives tab. From here, uncheck the Low Quality Studs checkbox. You may need to close and then open LDraw again to see the change.
Further update - as pointed out in the comments, I had incorrectly stated LDraw was the program that I use to export shapes to STL format. That program is actually LDView, and makes use of the LDraw library. I've updated the link to include the correct application. Apologies for the confusion.
Also, while I'm editing this, be aware that some of the shapes exported to STL format will need adjusting. Bushings and axles come to mind, as these parts will not fit together unless the axles are sized slightly smaller. Technic pins will also have similar issues due to the end flanges not being slightly chamfered as the are in real life. You'll need to make adjustments if you want some technic parts work together. Some parts also don't always correctly reflect that they have an "inside", so some areas of parts may print as hollow voids rather than with the desired infill. Check for this using your slicer software before printing.
1I think you may be conflating the LDRAW parts library and one of the tools that makes use of them. LDRAW itself doesn't have any menus to select preferences from. You could probably clarify which tool you were updating the preferences in for your answer to be slightly better. Mar 4, 2021 at 16:09
I will mark your answer as the right one, because of all the additional information that you provided - very helpful. But maybe add some links to LDRAW and general information as well, for this response to be useful for others.– jayarjoMar 8, 2021 at 7:15
You probably meant some software that has all the options you've listed but failed to mention. LDraw is just a parts library.– AlexMar 13, 2021 at 17:14
Most, but not all, existing LEGO oriented 3D modelling systems make use of the open source LDRAW libraries. Downloads, specifications, and more information can be found at https://ldraw.org/
Do you think mecabricks is also based on LDRAW models?– jayarjoMar 3, 2021 at 8:42
1I do not know for sure, you would have to ask the people who run the site. That said, since the LDRAW library had been available for a long time before MecaBricks was started it seems very likely that they may have started their parts library by either directly using LDRAW under the covers or by converting it to whatever format they use internally. I was not able to find anything on their site that said either way and they do not have the required license attribution on the site if they are or were using it. Mar 4, 2021 at 16:15
1@jayarjo Judging by this thread on the Mechabricks forum it looks like they're all hand modelled... Mar 29, 2021 at 11:00
There used to be PrintABrick, but the website has been down for ages. You can still find the code on github if you want to run it locally: https://github.com/hubnedav/PrintABrick