Stone clock?

[StuartBaker104]

Has anyone here ever made one of these? http://www.woodentimes.com/. There are a couple of places that sell plans.

I was looking at them the other day and later drove past a local granite supplier who has a waterjet cutter that will cut any shape. I've had an idea buzzing round my head since then about making a stone clock... wondering whether it would be possible to make a clock that would happily stay outside all year in british weather... pivots may be a problem, but brass shafts with stone sleeves might work.

Any thoughts?

[frenchie]

Friction might be an issue on all the gears (not the pinions, the teeth). But a fun project nonetheless

[Sleeper]

I had a customer order granite plates from Starrett to use in telescopes as temp stable baseplates.  They have the same expansion and contraction rate as both aluminum and borosilicate glass. So for securing the aluminum truss it was perfect.  I made the worm gear for his clock drive out of aluminum alloy for the same reason.  All this mass made his scope very stable.

All that said you could cut your gears from aluminum and hide that in granite. so it would look like great big granite wheels.       

[StuartBaker104]

21 hours ago, frenchie said:

Friction might be an issue on all the gears (not the pinions, the teeth). But a fun project nonetheless

Yes - will need to find out how good the cut surface finish could be. I had imagined glued in brass bushes for the pivots.

19 hours ago, Sleeper said:

I had a customer order granite plates from Starrett to use in telescopes as temp stable baseplates.  They have the same expansion and contraction rate as both aluminum and borosilicate glass. So for securing the aluminum truss it was perfect.  I made the worm gear for his clock drive out of aluminum alloy for the same reason.  All this mass made his scope very stable.

All that said you could cut your gears from aluminum and hide that in granite. so it would look like great big granite wheels.       

Thanks - this is useful. Never really thought that hard about it before, but CTE is a a good reason for using brass plates with brass wheels. Not sure that aluminium gear teeth would last that long however. Part of my idea was that granite is rock hard and wouldn't wear.

[dadistic]

You might try checking this out for ideas on long lived outdoor clocks.

Clock of the Long Now

[StuartBaker104]

Thanks! I had something smaller in mind 

[dadistic]

On 4/7/2017 at 1:48 PM, StuartBaker104 said:

Thanks! I had something smaller in mind 

I imagine so

Still, you might be able to make use of ceramic bearings like they do for the wheels. Try a search for ceramic skate bearings, and Silicon-Nitride Ceramic Balls etc.

[Sleeper]

On ‎4‎/‎6‎/‎2017 at 4:02 PM, StuartBaker104 said:

Yes - will need to find out how good the cut surface finish could be. I had imagined glued in brass bushes for the pivots.

Thanks - this is useful. Never really thought that hard about it before, but CTE is a a good reason for using brass plates with brass wheels. Not sure that aluminium gear teeth would last that long however. Part of my idea was that granite is rock hard and wouldn't wear.

   

Granite is not just solid stone, it's mostly chucks of silicates like quartz so it is very hard like glass but all pressed together like a huge block of broken bits.   

As a surface it is abrasive. When I tested metrology tools I would test gage blocks and the granite plates for wear.  It tended to be the hardened steel gage blocks that would show wear from being used on the granite plate. Granite plates are slightly porous while being very flat and harder than steel. So the flat gage blocks can be moved around with digging in or sticking. It is a ultra fine abrasive.  

You may want the teeth to have a smoother, less abrasive wear surface like steel or a ceramic. The granite would be a great backing to that surface. Think like a dental crown for teeth. I think as gears the granite wheels would eat themselves up.   

In France there are a great many abandoned mill stones. Many are dark Alpine Granite. Some are hundreds or thousands of years old. Those might be great for your project.  Possibly even very inexpensive.  Here in the states a great many have been imported to be re-used as mill stones. A water powered grain mill in Waco Texas has two pairs of French stones. The miller says as long as they don't touch the stones last forever.   

I wish you great Success!  

 

         

[StuartBaker104]

Hmmm, beginning to think this might explain why no-one is selling one anywhere...