Purpose of End Stone (jewel)

[kd8tzc]

Hi, as someone new to the hobby of watchmaking, I'm puzzled by the purpose of what the end stone is.  I notice it seems they only occur on the balance wheel, and only on the balance wheel do we ever talk about shock protection, so does it have to do with that?  I guess I'm struggling how a little piece of a gem helps with that.

Anyhow, I'm hoping someone can point me to something that would explain this all.

[Nucejoe]

This is copied from an online source.

Cap Jewels: Some bearings utilised cap jewels, sometimes known as end stones or ‘capstones’. This bearing structure operates similarly but has a second outer jewel, which sits at the very tip of the gear shaft. This has several effects. Firstly, a small oil reservoir is formed between the two jewel layers, ensuring continuous lubrication for the fastest-moving parts such as the balance wheel. Secondly, they allow the shaft to be constructed in a conical shape, which prevents oil from seeping down the arbor and stops the shoulders of the arbor from rubbing against the jewel, which would negatively impact accuracy. These caps also prevent the arbor from moving up and down during rotation

Rgds 

Joe

[spectre6000]

I recall a fairly in depth conversation on this a year or two ago. Diagrams and everything. Worth a search.