A Mini Tower Clock

[crueby]

As usual, I don't look in for a week and there you are, well into another fine project!!

Between you and Kim, your clocks are making me want to do another one. I just need to dust off the 3d printer and get some filament.

I'll have to import some shop elves though as mine all left home!

Cheers

Maybe design one up as some sort of engine with pistons going round with the second hand?

I am thinking of a 21 day run time with a moon phase dial.  Maybe

That would be great!

[crueby]

Got first one of the spring drum gears cut - these are the largest at 90 teeth.

and this morning cut the second one. Here is the growing herd of gears so far:

Two more to cut - the 72 tooth gears that go on the taller holder up to the escape wheel. I skipped over to the largest ones since the 72 tooth gears need a different arbor, with a smaller center screw.

[cnr6400]

  You're going to have to think about hiring a gear wrangler to manage that herd... luckily you don't have to drive 'em all the way to Yuma...

[crueby]

  You're going to have to think about hiring a gear wrangler to manage that herd... luckily you don't have to drive 'em all the way to Yuma...

Well,the sporting goods store sells Gear Bags...      Then I  can just catch the 4:10 to Yuma!

[Kim]

That is quite a pile of gears!   

But you're a few wheels short of a load! 
I'm sure you'll correct that soon!

Kim

[crueby]

That is quite a pile of gears!   

But you're a few wheels short of a load! 
I'm sure you'll correct that soon!

Kim

True! Just wheeling in circles!   

[Roger B]

Splendid work on the gears    SO much attention to details 

[crueby]

Thanks Roger!   

[crueby]

Down to the final two gears!  (well, so I thought, read on)  The 72 tooth ones are the easiest of the set to do, since at 5 degrees per tooth the rotary table advance was just one full turn, 0 to 0, for each tooth. No tracking the sequence, checking off each cut as I went.

Even the shop elves got in for a 'turn' at the handwheel...

Here is the full set of gears:

WEEEELLLLL, not quite.  There is a whoops in the spreadsheet! There is one more 15 tooth gear needed, for the shaft with the escape wheel.      Found that out when I laid out the gears in order, on the shaft locations they go on. And it didn't add up! Went back and looked at the CAD model, and counted up the pinion gears, and realized that there are FIVE 15 tooth gears, not four.  Apparently the shop gnomes are getting REALLY good at stealing small shiny parts - they got this one on the computer before I even made it!      Easy fix since the setup was still in place on the mill - just had to swap back in the arbor and make a new small blank, swap back to the #2 cutter, and make the passes for the 15 tooth pinion.

So, next steps? I need to broach some 1/16" keyways in the gears that go on the 1/4" shafts, they will be under the most pressure so keys are a good safeguard over solder or loctite. Then I can start making all the pivot shafts. Some of them get other fittings, like the spring drum ratchet, and the minute shaft slip spring pieces to allow setting the time. It may look like the clock is almost done, but there are a LOT more parts to make - lots more fun in the shop!
 

[Sanjay F]

I've always wondered about clocks and watches; when the gears mesh the friction must progressively increase with the more gears you have. Do the gears run dry or are they oiled and what does the oil actually do as it must make contact for the briefest of moments as a set of teeth engage and disengage?

You can tell I know NOTHING about gears and gearing! 

[crueby]

I've always wondered about clocks and watches; when the gears mesh the friction must progressively increase with the more gears you have. Do the gears run dry or are they oiled and what does the oil actually do as it must make contact for the briefest of moments as a set of teeth engage and disengage?

You can tell I know NOTHING about gears and gearing! 

Good question!  One thing that is different than most gear usage is that clocks gear up rather than down - in your car, for example, the engine spins much faster than the wheels, so the gears in the transmission reduce the speed out the output shaft. In a clock, its the other way around - one turn on the power shaft (whether its driven by weights, springs, whatever) can turn the escape wheel at the other end of the train thousands of times. So, its a balancing act of how much spring-force/weight it needed to get just enough power at the far end to give the pendulum a little nudge every time the escapement trips to the next tooth - you want just enough to keep the pendulum going, not su much that you fling it into the next room, and not so little that it stops running.
Clocks normally are run with no lubrication on the gear teeth. They run so slow that its not really needed, so slow that there is no heat buildup, the normal brass-on-brass gear teeth do not tend to gall on each other, and any oil on exposed gears would collect dust/grit/pet hairs/etc that would clog things up. Even without any lubrication on the gear teeth, I've had to clean out dog hair from my mother's Cuckoo clock gear train!
And for a clock, there is constant pressure on the teeth of all the gears up to the escape wheel - if it was not for the escapement, the gears would keep turning and unwind the clock pretty quick, while whizzing the hands round and round! I have clocks with 6 or 8 pounds of weight on the drive shaft, and out at the escape wheel the force is tiny, ounces or less.
Yes, there is more friction loss with the more gears you have - am sure there are books full of formulae on how to calculate it, but its not that important for me to understand it at a deeper level.
Hope that helps?Chris

[Sanjay F]

Excellent explanation, thank you; I always wondered and never asked or looked it up!

This point is the one I'll take away 'One thing that is different than most gear usage is that clocks gear up rather than down' - I'd hadn't thought about that 

[internal_fire]

I have built a couple of 3D printed clocks using the designs and files from Steve Peterson. (Steve's Clocks)

In the instructions he points out that an 8 day clock using a 7.5 pound weight with a drop of 4 feet will have a residual force at the escapement of 0.019 ounces. This is less than the weight of a house fly. If a fly were to land on the escape wheel the clock would stop.

The potential energy in a weight that drops is easily calculated. Then divide by 700,000 or so to determine the energy remaining for a single tick or tock.

Obviously, any sort of losses in the gear train are bad.

Gene

[crueby]

I remember seeing a show about the clock in the tower at the parliament building in London - the clock there has a very large pendulum, and they tweak the period on it by adding small coins rather than changing the distance of the pendulum bob from the pivot! Amazing how small the forces are in even a large clock. On my wall clock, with a 1 second tick and a 3' long pendulum with a fairly heavy bob, it can be stopped in the summer if it gets too windy when the windows across the room are open.

[Kim]

I remember seeing a show about the clock in the tower at the parliament building in London - the clock there has a very large pendulum, and they tweak the period on it by adding small coins rather than changing the distance of the pendulum bob from the pivot! Amazing how small the forces are in even a large clock. On my wall clock, with a 1 second tick and a 3' long pendulum with a fairly heavy bob, it can be stopped in the summer if it gets too windy when the windows across the room are open.

Hmm...    That's interesting...  Because the weight of a bob does not affect the period of the pendulum.  Only changing the length does. So, adding coins to the bob must change the center of mass of the bob, thus making very tiny changes to the effective length of the pendulum!  That's fascinating!

Kim