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Discussion in 'Tower, Monumental & Street Clocks' started by Tinker Dwight, Nov 16, 2012.
I'm curious. Why don't I see many tower clocks with chains instead of
Do you like bicycle chain and sprockets?
They don't have to be that size as there are a range of chains for all types
of loads and they are quite efficient.
Roller chain wasn't available until after about 1880, long, long after tower and or turret clockworks were designed. Prior the the roller chain invention, only simple link chains were commonly used which wear badly and are prone to stretch badly. Such would make for a miserable clock movement.
That said, fusee chains were well accepted as an improvement over gut to couple the fusee and mainspring barrel but there it was a matter of strength and durability as the fusee is only used to deliver force to the escapement and does not bear into the wheel-pinion system.
Finally, the design of clockworks and in particular, tower and turret clocks is and was a traditional craft and not one friendly to change.
It would be a lot more difficult to get each wheel to rotate opposite to the one mated to it with chain. Seriously, chains have been used to lift weights, but not to wind up and store on the drum like manila rope or wire rope. It also takes some extra parts to do the job to, not to mention the storage box for the chain. The chain formerly used was "like" bicycle chain except that the links fit between the sproket teeth (2) and the stuff would be damn heavy to carry up flights of stairs & ladders if one needed to replace it. Replacement cost whould be tremendous too. I think I know of only one clock in my area still using chain. Oh yeah, chain doesn't twist too easily and might not work where you have to route the chain through to odd locations which is the case on some clocks with wire rope.
Do you mean chains for winding the Strike?
Far too much mass, too much inertia to overcome at each cycle of the anchor, too much slack in the chains. i doubt very much it would ever have been considered, but if it bever had, i am certain it would have proven impractical, and likely would not have worked.
From a design and engineering standpoint a gear train has a number of advantages over a chain. For example; most clock trains have a gear ratio of about 8:1, wheel to meshing pinion, usually using pinions of 7 or 8 leaves, and in tower clocks sometimes 10 or 12 leaves. Now, the spacing between the teeth in most of these wheels is of course dependent upon the size of the mechanism. Let us assume that the pitch spacing of the teeth on the gear is 1/4" And let's assume the gear has 96 teeth. That would then suggest the gear would have a circumference of about 24" or a rough diameter of about 8 inches. While chain is available in 1/4" pitch most roller chain starts at about 1/2" pitch. Simply put a gear versus roller chain comparison would suggest sprockets would be about 2x the size of gears/pinions. There is no need to reverse direction in a clock movement if all the sprockets rotated clockwise, no issue. Now, if we double the size of a wheel by making it a sprocket it will weigh about 4 times that of the same ratio gear resulting in much more inertia to overcome, much more friction losses in pivots, on and on....
Also to be considered are the physical requirements of small number sprockets. There is a minimum size of sprocket for a 1/2" roller chain, I think it is considerably higher than say 8 teeth...hence to obtain the required ratios the larger sprockets will all need be higher counts, consuming even larger amounts of energy and space.
In closing, can it be done? Certainly, I have seen several chain based clock mechanisms over the years. One of the fellows who builds large sculptural wood works clocks uses bead chain in bead sprockets. Some of his wheels are 24” dia or larger. I also have a friend who has tried a large display clock using chains and sprockets for the various gearing ratios, ended up being fairly ungainly, it does work, but it consumes a lot of power IMO. Inertia and friction...... he has gone back to wheels and roller lantern pinions and is now attempting a clock with a 4' diameter freestanding aluminum ring gear (spokeless open center).
I have also considered using Gates minature timing belts and sprockets instead of chains/sprockets. Would also work, and have less issues than chains IMO.
FYI, a Howard and Davis still running with chain drive for time and strike. Dates to the civil war period from what I understand.
The clock he has doesn't seem to have any maintaining
part unless it is hiding some place.
The strike seems to be disconnected and not
used. Only the time side seems to be running.
I can't really tell on the time side if there is maintaining mechanism or not. Most Howards' have it originally. And in this case it may well be a Huygens endless loop chain drive that provides maintaining power while being rewound any how....
Sorry the first picture in #9 slot doesn't show anything. Went there today & will show the device. Because the wood enclosure is too tight to fit the camera in, the picture of it engaging the third wheel of the clock is not possible. 4 shots 1, on the frame. 2 part removed from the clock. 3 another view 4 still another view.
The pin is bent in the photos, but it was straightened afterward.