Hopefully this is a simple question for the watch experts out there.
Why did they put gem stones, such as Rubies, in watches? What purpose did the stones have? Do they still use gem stones for expensive watches?
They are used as bearings for moving parts due to the low friction and good wear characteristics. Low friction equates to increased accuracy in watch movements, so better watches use jewel bearings, even to this day.
Yes, they still use gemstones in watches – and not necessarily expensive ones. Expensive watches do tend to contain more of them though. (For example, my Rolex GMT-2 – a very “middle class” watch – has, I think, 32 gems; and my old Seiko Bell-Matic has, IIRC, 7.)
I don’t know for sure why there are gems, but I believe it is because their bearing surfaces do not wear as fast as a metal bearing surface would.
Any time you have a machine with moving parts you will have places where bits rub against other bits. Call these ‘bearing points’. My understanding was that they used jewels at these ‘bearing points’ because jewels would last longer &/or have lower friction than metal. Perhaps someone with more direct experience with watch design will come along and correct me, but that’s my opinion at this point.
Man it’s hard to be first around here. I’ve gotta learn to type faster!
So, why do there always seem to be an odd number of jewels in a watch? e.g. 17 jewels.
I’m pretty sure that the rubies in most pocket and wrist watches since the early 1900’s are synthetic, not natural. They have the same properties, and were cheaper and more dependably available at the time.
Synthetic ruby or spinel is used for the mechanical stability, low friction, etc.
The red of the ruby sets itsel off, is pretty, easy to see (particularly for a watchmaker), and has a customer appeal.
I also hoped that my cite above would explain about odd jewels, rather than even numbers.
“Jeweled” movements are used because the shafts and parts in question are far too small to have a conventional ball or roller type bearing, and even too small to have a decent bushing.
If you just set the shaft in a drilled hole, the metal-on-metal contact would eventually cause wear, sloppiness, and either stoppage or at least inaccurate timekeeping.
A jeweled bearing is simply nothing more than a tiny cylindrical slug of some gemstone, with a very precise and smooth conical recess in one face. The gemstone is used for its hardness and thermal stability.
The shaft that rides in this bearing is pointed to match the recess in the jewel, and also carefully hardened and polished. This creates a very smooth, long-lasting bearing, with a minimum of parts and requiring a minimum of maintenence. (You don’t oil a jeweled bearing.)
This is a perfect application for the concept- the parts are tiny, light, and don’t produce a great deal of speed (if a shaft were doing 1,000 rpm, it’d overheat and shatter the jewel, but naturally, watch parts don’t move anywhere near that fast.)
Here’s a place where you can buy them for your own projects.
Closed end pivot bearings are used for the light duty parts.
Many if not most of watch jewels are journal type, a cylindrical shaft running in through hole. Open the back of a (pocket) watch and observe the ends of shafts!
I understand that one American brand (Waltham) used DIAMOND jewels in its watches. Of course, these were mostlt a giimic-the coefficient of friction of diamond and ruby are probably pretty similar. Does anybody know if other brands used diamong jewels?
They didn’t use diamonds for all the bearings, IIRC. They just used one diamond endstone as a gimmick. The basic bearings were probably ruby.
Perhaps others used the same sales gimmick.