Additionally, all of these file sharing websites are kinda a beginner's thing. They are only really useful for trinket type sculpted objects. When it comes to functional prints, there is a lot of subtle details required for proper design. You will quickly learn that fasteners, and print tolerances required to replace metal fasteners is very print, material, and printer specific.

I know my exact tolerances in every orientation on my Prusa. When I design, these elements are built into that design. I do not care about calibration. Anyone that obsesses with calibration is doing so in order to transfer designs between machines. If you make your own designs you just need to dial in the tolerance locally. If you really need a 9.95mm part dimension with a 10mm slot in some object, it is extremely easy to do in CAD. Just print a unit test of a slice of the object in question in the same orientation and manually measure all relevant dimensions and tolerances. Let's say you measure 9.98mm when you dialed it to 9.95mm. Which side needs to be adjusted might be a factor too. All you need to do is go into the CAD and change the dimensions to 9.92mm with the change oriented correctly.

By design these are ultimately precision machines without accuracy. The 0,0 home location is always different, but all motion is relative to this location. Calibration is trying to create transferable accuracy in a precision system. The deeper you get into this, the more it becomes an issue. Tesselated object files are also an extremely poor way of transferring designs because it bakes in the precision versus accuracy bias.

If you are unaware, the issue with files needing tessellation is because of π being infinite and all computers truncating infinite floating point values.

A slightly better solution for small file sharing is to post STEP files. These are the real dimensions with π as generated by the CAD hierarchical tree, but without the full tree. The STEP file can be imported in CAD and further refined through new operations and importing edges from the STEP file. However, if you go down this path, you will likely find that only beginners and extreme amateurs seem to share their designs even at this level of sharing STEP files or even the large CAD files too.

One of the most critical advanced CAD skills is knowing where to place an object's origin and how to dimension everything relative to critical dimensions. This gets into the topological naming issue of how CAD works under the surface. Basically there are a ton of ways to do CAD wrong. There are many CAD operations that exist for very specific niche case reasons, but are never supposed to be used within the main hierarchical tree. If this is done wrong, it will create multiple stacked references to truncated π and this will break the CAD part every time, especially when making any further modification. I often have this happen at a couple of stages within my own very complicated designs. This is very typical in a CAD design workflow. The solution is to stop and rebuild the entire part from scratch while building the proper order of operations or a better origin for the part. I usually rebuild a part at least once or twice before printing complex stuff and assemblies.

In the past I tried printing stuff from places like thingiverse, but it was fiddly and nothing worked very well. I started importing them into FreeCAD and just rebuilding them with the part as a reference, but even this sucked. My only use for these websites now is for ideas I might integrate into my own designs. I can make anything in CAD properly and faster than I can print the whole thing twice. That is the full learning curve of 3d printer file sharing. It is also why selling files is not really a major business thing that takes off. That would only be possible with accurate machines. Precision is cheap, accuracy is not.