Optimal Surface Finish For Bearing Surfaces

[Joe S]

In a recent thread, someone commented that a bearing surface with fine scratches was better than a highly polished surface, because the fine scratches helped to retain lubricant, and reduced the load bearing area where the adjacent parts made contact.  What grit of polish will produce the optimal level of surface roughness for bearing surfaces?

[David Veith]

think of Jeweling a bolt on a modern gun.
David

[Dphariss]

In a recent thread, someone commented that a bearing surface with fine scratches was better than a highly polished surface, because the fine scratches helped to retain lubricant, and reduced the load bearing area where the adjacent parts made contact.  What grit of polish will produce the optimal level of surface roughness for bearing surfaces?

As fine as possible, well within reason anyway.
Ever see a rough ball bearing?
Polish to 600 grit and caseharden the lockplate. Use a good light weight lubricating oil sparingly. Even 600 grit is not "smooth"
In a good the tumbler should only touch the lock plate at a narrow right around the tumbler hole.
Dan

[flintriflesmith]

Even a highly polished surface has huge scratches in it when viewed by an electron microscope. These are at the molecular level when lubrication works. Scratches you can see with the naked eye are like canyons. (The same is true of the sharpest chisel or knife edge.)

I think Dan nailed it with his comment about ball bearings.

On the other hand, friction, lubrication and wear are not really a big deal in a flintlock comapared to a wheel bearing in a car going 75 miles and hour or the sliding parts of a modern rapid fire gun. It would be real easy to get carried away with polish and lub oils that go way beyond what this 200 year old technology really requires!

Gary

[T*O*F]

In a good lock the tumbler should only touch the lock plate at a narrow right around the tumbler hole.

That is known as a "freed" lock.  On the best locks, this bearing surface exists on both the plate and bridle sides of the components.  These are known as "double-freed" locks.

I notice that many Davis locks are now double-freed.