Comment by Arch-TK

You're better off for having done the measurements.

Broadly, it is just good training since you're normally _not_ going to have CAD drawings. If you do this enough, it becomes second nature, and with a 3D printer it's fast to make test prints which you can use to check your measurements against.

More specifically, it avoids having to wonder if you'd be breaching some law by using those CAD drawings to make a "derivative work". While there's nothing illegal about using precise tools to measure an existing product and create a CAD model. It's (apparently) a silly grey area to take measurements from a CAD representation of a product to make your own CAD model. It can be argued that you're just taking factual information from a reference and using it to produce your own design. But whenever you find yourself saying to yourself that something "can be argued" then you really need to take pause to consider if you want to find that out for yourself or avoid the problem entirely.

This is the same absurd nonsense that Prusa's "Open" Community License imposes. If I buy a Prusa 3D printer and I just carefully measure it (I don't find this that hard, and I am at best an amateur, consider what an experienced CAD designer could achieve with the right tools), I can create a 3D model of the printer and, as long as I've omitted any separable purely aesthetic elements, I own all rights to that 3D model.

Moreover, as long as there are no patents on the product, I can manufacture and sell it.

The hard part of cloning a product like a 3D printer or silent fan is not in getting the exact CAD model, it's in the choice and sourcing of materials, making the right tooling, finding places to make all the parts, etc.

There are also some secrets on how certain things are manufactured. But those either don't appear in the CAD model or can be easily omitted.

If manufacturers want to hand out CAD models of their products, they should do so under some highly permissive license, with only enough detail to actually aid in producing mods. The alternative where the license is restrictive, is that you're just giving out poisoned apples that solely restrict the freedoms of anyone who decides to take them.