the etymology of "break-in" for mechanical items

Factual Questions
1

New cars often come with instructions to operate the engine for the first several hundred miles in specific ways intended to cause the parts to wear, just a little bit, until they fit each other “better” than they did at the factory. Here, “better” means (for example) that machining marks get worn away, microscopically sharp edges get worn off, and piston rings and cylinders seal better and lubricate better so they will then be able to tolerate the expected operating loads and RPMs for a few thousand hours.

Other mechanical equipment (electrical motors, air compressors, etc.) sometimes specifies a similar schedule of operation in its initial hours, also typically called a “break-in” period.

What is the etymology of “break-in” in this context?

Is it related to the machine shop practice of “breaking” freshly machined edges by rounding them with a hand file or a deburring tool?

Does it come from the practice of “breaking” horses to prepare them for a life of servitude?

…Something else?

2

I assumed it was like daybreak - but that is just an assumption on my part.

3

Its a term that was is used with horses (since before mechanics)
Its the first step of training, or taming, a horse…

4

As an engineer, I hear the term “wear in” a lot more than “break in.” I always assumed it was a back-formation from “wear out,” as in a device reaching the end of its life. I think “break in” applies more to situations where you have to work out some initial stiffness, as in a new catcher’s mitt.

But that’s all just my opinion and my anecdotal experiences.

5

This is my experience as well; doubly so as I once played baseball.

On a related note, this reminds me of a similar expression: “bedding” an engine. I presume the usage was denoting running the engine for a short time to allow the various parts to settle.

6

You still hear about “bedding (in)” new brake pads…that seems to be the accepted term there.

As far as “break-in” on an engine not being an engineer’s term, it seems to be used in owners’ manuals and the like…although that could just be the deliberate use of a n accepted layman’s term for the benefit of the end user, I guess.

Certain formulations of motor oilare sold as “break-in oil,” to be used on freshly built/rebuilt engines…so it seems like a pretty accepted term among engine builders.

7

In the UK the phrase is/was “running in”. In the olden days, when cars needed a lot of running in, you used to see signs on the back of carsYRBSEcyFluMw~~60_58.JPG) reading “Running In: Please Pass”.

8

Huh, I’ve always heard it referred to as “seating” brakes. This is the first time I’ve heard “bedding” in that particular application.

9

I just did some google testing. With quotes:

“bedding in brakes” 25,600 results
“seating brakes” 5,340 results (including some on the first page that say "Huh? The correct term is “bedding in,” haha)

Might be a regional thing.