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small.planes
02-14-2015, 01:52 PM
Evening all,
Wheels (the big gears ;) )are usually made from brass, and run against hardened steel pinions.
Is there any reason that steel running on steel isn't normally used?
Id harden both, and the wear a clock sees should not be very large I would have thought...

Dave

(Shocked at the price of large pieces of brass....)

Rosco-P
02-14-2015, 02:03 PM
No personal experience making or repairing mechanical clocks. This insight comes from my neighbor who did. The little pinion teeth get proportionally more wear, steel lasts longer. Clockworks usually get oiled at time of manufacture and when they get cleaned and repaired. Not so often in-between.

gvasale
02-14-2015, 02:08 PM
It could be tradition; possibly to minimize the effects of magnetism. Some old stuff has lots of cast iron running against other iron/steel. Maybe its because brass is easier to machine than steel.

You now have three guesses. I do know where steel & brass run together, the steel usually shows more wear.

Lots of industrial gear sets use sreel on steel, but they use cycloidal tooth profiles in clocks rather than involute.

WRT Rosco's reply, clock wheels & pinions never get oil on the teeth except...the escape wheel.

Rosco-P
02-14-2015, 02:45 PM
WRT Rosco's reply, clock wheels & pinions never get oil on the teeth except...the escape wheel.

Okay, I have introduced some confusion. My statement was about the infrequent oiling of mechanical clock's pivot points. Much of my neighbor's boniness came from neglected clocks, repairing and replacing parts that had been run to death through lack of lubrication. Occasionally he'd get a clock with a broken mainspring.

Baz
02-14-2015, 03:01 PM
On the old cheap alarm clocks we used to have the spring barrel and next wheel were often steel, probably for strength and were not crossed out perhaps since they moved slowly did not need the mass reduction. Later wheels in the train that had to move faster would be crossed out by punch so perhaps that was not so easy in steel.

A.K. Boomer
02-14-2015, 03:28 PM
I think the little gear big gear theory works well, make the smaller one out of something that's more durable,

also - there is the compatibility issue, sometimes metals of same likeness do not do well in contact with each other under pressure, can accelerate wear on the smaller gear,
on the flip side others do very well, iv heard certain brass being described as having some self lubricating properties when paired with other metals,,,

heck in some cases of high vibration and the like nylon will outlast steel simply for adding a dampening effect...

mars-red
02-14-2015, 03:50 PM
Theoretically perfect wheels and pinions should not be subject to any sliding friction (they should roll across each other). In the real world, however, there is some sliding friction. Using dissimilar metals should be better for that, and I think certain brass alloys have a small amount of self lubricity. I would worry about excessive friction due to galling with steel on steel.

EDIT: Cross posted with Boomer there, I agree with what he's saying.

Mark Rand
02-14-2015, 05:41 PM
Does that apply to cycloidal teeth? or does is apply specifically to cycloidal teeth? I'm trying to remember the specific reason for using them in horology.

Bob Fisher
02-14-2015, 05:50 PM
One manufacturer at least built movements of steel. That included plates, and wheels. The wear usually incurred in clock movements is always at the pivots as opposed to the wheels themselves. Bob.

gvasale
02-14-2015, 07:30 PM
Gilbert made clocks in the WWII era with steel plates and brass bushings mashed into place. Brass wheels with the usual lantern pinion with bass ends & steel trundles.

I have an old tower clock ca 1810 with cast iron wheels and steel or some ferrous arbors & pinions. I don't think they were wrought iron. I don't really know how wrought iron was used in applications.

Cheep alarm clocks were almost always made of steel in the late 19th century an on, nothing meant to last decades. That is untiol the use of some zinc alloys or plastic became more prevalent.

I would say involute gears are supposed to tolerate sliding friction. Cycloidal gears I have been told have engaging & disengaging friction and are described as having more disengaging friction in operation.