Q. How do I use 3D scanners to make an exact replica of a small part?

The marketing around 3D scanners makes this process seem like it's a lot simpler than it is. Virtually every manufactured part nowadays has been designed using Computer Assisted Design programs before it was physically produced, and when trying to make repairs it would be really useful to have those CAD files available.

Unfortunately, very few companies are willing to release these types of designs to the public, so contemporary DIY repair methodologies often entail re-modeling existing parts in order to re-produce them.

3D scanning promotional videos and websites will try to make it seem like 3D scanners are going to make this job easier - in reality it's just trading out one set of problems for another, and even with very expensive 3D scanning setups, there is still a considerable amount of cleanup that needs to be done before a part is able to be fabricated.
It is often easier to use scan data as a reference image in the modeling process, rather than envisioning the scan data as the CAD -> CAM file itself.

In Fall 2020, the FabLab's 3D scanners are not accessible in our flipped service model. You can create a moderate-resolution 3D scan using your own camera (phone photos can work just fine!) using photogrammetry software.
Autodesk ReCAP Pro is available free for students to use in non-commercial work: https://www.autodesk.com/education/edu-software/overview?sorting=featured&page=1