Author Topic: Inertia  (Read 2589 times)

Offline KKC

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Inertia
« on: February 29, 2016, 02:04:18 PM »
I'm reading Clayton Boyer's Guide to Clock Design and he's discussing Inertia.  Inertia=MassxRadius².

What has been everyone's experience on this.  He's discussing how big wheels require a lot of weight to get over the inertia big wheels need in order to operate and that inertia is compounded through the entire train. This is important to me as I would really like to design a large wheel clock.   

Thoughts, experiences or comments anyone?
« Last Edit: February 29, 2016, 02:10:26 PM by KKC »

Offline jss

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Re: Inertia
« Reply #1 on: February 29, 2016, 07:12:50 PM »
« Last Edit: February 29, 2016, 07:17:50 PM by jss »

Offline KKC

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Re: Inertia
« Reply #2 on: March 01, 2016, 06:00:31 AM »
JSS you are da bomb!!! Thanks... I'll read up on those. 

Offline KKC

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Re: Inertia
« Reply #3 on: March 01, 2016, 12:13:43 PM »
Okay... First I'd like to say it truly sucks that I'm coming in on the tail of this fad of wooden clock making.  It would appear that no one does this anymore.  It's frustrating to be reading threads from 2007 with links to websites that no longer exist. 

Thank God Gary's Clocks is still up.  He has been VERY informative. 

And by the way JSS, I contacted the guy from timeshapes and asked him some questions.  Apparently he doesn't reply to questions about clock making. 

Offline KKC

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Re: Inertia
« Reply #4 on: March 02, 2016, 05:58:24 AM »
After watching Gary's Clocks on Inertia I wonder this.  Rather than make a large escape wheel why not just have a large center or 3rd wheel and just keep the escape wheel normal size?  Anyone know if that would work?

Offline steve323

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Re: Inertia
« Reply #5 on: March 04, 2016, 06:45:02 PM »
Hi KKC,

I would say that people making their own wooden clocks has a very long tail stretching back for hundreds of years.  Very few people work on farms anymore.  Very few people even need to know how to fix anything because they can just throw it away and buy another one. 

As far as your question on the escape wheel, yes it seems like you should be able to keep the escape wheel normal size and scale everything else.  The escape wheel needs to start and stop with each tick of the pendulum.  A standard 1 meter pendulum would do this 30 times per minute.  All the other wheels also start and stop with each tick, but they have progressively smaller movements because of the gearing down.  This gives them a lot less momentum to overcome.  The escape wheel moves the fastest so it has the most impact from the start/stop action.  There is a clock with a rotary pendulum that avoids this start/stop action, but it requires more gearing to push the pendulum around at 1 revolution per 2 seconds instead of 1 revolution per minute.  I may attempt a rotary pendulum for my next clock design.

My last clock design uses an 18 tooth escape wheel to help keep the inertia small.  This means that it rotates every 36 seconds and needs to be geared down differently than a "standard" clock.  I use the following gear ratios

36 second escapement
50:10 = divide by 5 = 3 minutes
50:10 = divide by 5 = 15 minutes
48:12 = divide by 4 = 1 hour (minute hand)
48:12 = divide by 4 = 4 hours
45:15 = divide by 3 = 12 hours (hour hand)

btw KKC, how do you like the pdf from Clayton?  I am thinking about getting it, even if it is just to help out one of the last wooden clock makers.  :)

Thanks for the links JSS.

Steve

Offline KKC

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Re: Inertia
« Reply #6 on: March 07, 2016, 12:49:05 PM »
Hi KKC,

I would say that people making their own wooden clocks has a very long tail stretching back for hundreds of years.  Very few people work on farms anymore.  Very few people even need to know how to fix anything because they can just throw it away and buy another one. 

As far as your question on the escape wheel, yes it seems like you should be able to keep the escape wheel normal size and scale everything else.  The escape wheel needs to start and stop with each tick of the pendulum.  A standard 1 meter pendulum would do this 30 times per minute.  All the other wheels also start and stop with each tick, but they have progressively smaller movements because of the gearing down.  This gives them a lot less momentum to overcome.  The escape wheel moves the fastest so it has the most impact from the start/stop action.  There is a clock with a rotary pendulum that avoids this start/stop action, but it requires more gearing to push the pendulum around at 1 revolution per 2 seconds instead of 1 revolution per minute.  I may attempt a rotary pendulum for my next clock design.

My last clock design uses an 18 tooth escape wheel to help keep the inertia small.  This means that it rotates every 36 seconds and needs to be geared down differently than a "standard" clock.  I use the following gear ratios

36 second escapement
50:10 = divide by 5 = 3 minutes
50:10 = divide by 5 = 15 minutes
48:12 = divide by 4 = 1 hour (minute hand)
48:12 = divide by 4 = 4 hours
45:15 = divide by 3 = 12 hours (hour hand)

btw KKC, how do you like the pdf from Clayton?  I am thinking about getting it, even if it is just to help out one of the last wooden clock makers.  :)

Thanks for the links JSS.

Steve

Well Steve I don't know a lot about clock making yet so I don't know if Clayton's pdf is good enough to justify $42.00 bucks.  I had sent you a couple personal messages on this board did you get them?

Also I cannot figure out how to calculate my gear ratios and counts like you just showed in your post.  How do you come up with those numbers? If I can get this part figured out I'd make a major breakthrough.  Right now I'm just sticking with the 64x8 and the 60x8 wheels and pinions and a 30 tooth escapement. 

I want to design my own clocks like Clayton.  I have AutoCAD so my plans are limitless.  I just have to learn how to do the design side of things. 

Offline steve323

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Re: Inertia
« Reply #7 on: March 09, 2016, 08:47:36 PM »
Hi KKC,

I often lie awake at night thinking about the gear ratios in clocks.  Ultimately, there are only 2 criteria that matter.  The minute hand needs to rotate once per hour and the hour hand needs to rotate every 12 hours.  Both need to rotate in the same direction.  Adding a second hand is an optional 3rd criteria.

The gearing between the minute and hour hands is relatively easy. The divide by 12 ratio is done with gears that divide by 3 and divide by 4.  One easy way to do this is with a 30 tooth gear meshing with a 10 tooth gear for a divide by 3.  The second set of gears uses 32 teeth meshing with 8 teeth for a divide by 4. 

Another set of calculations takes place between the pendulum and the minute hand.  The length of the pendulum determines the overall ratios.  Wooden gear clocks usually have 39" pendulums with a period of 1 second in each direction, or 2 seconds for a complete back and forth swing.  Most clock designs use a 30 tooth escapement.  Pairing a 30 tooth escapement with a 39" pendulum would result in the escapement rotating once every 60 seconds.  It needs to be divided by 60 for the minute hand to rotate once per hour.  The traditional way to do this is a 64:8 set of gears driving a 60:8 set of gears.  The first set has an 8:1 ratio and the second set has a 7.5 ratio.  8 times 7.5 is 60.

There are other ways of achieving the 60 to 1 ratio between the escapement and the minute hand.  5 * 4 * 3 =  60, so you could have a 5:1 ratio, a 4:1 ratio, and a 3:1 ratio in the gears.  The 5:1 ratio could be built using a 50 tooth gear driving a 10 tooth gear, or a 40 tooth gear driving an 8 tooth gear.  The minimum pinion size is usually about 8 teeth.

Steve

Offline KKC

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Re: Inertia
« Reply #8 on: March 10, 2016, 06:42:54 AM »
In Clayton's PDf he discusses the length of the pendulum and how everything is then calculated from that.  So according to him determine the length of pendulum and move to calculating the gear ratios from that.  Now in his example he is leading me through the building of a simple I think it was 3 or 4 wheel clock.  The example he's using is a one second swing of the pendulum.  I get that.  He then goes on to explain that 60 tooth wheel and the 8 tooth pinion as well as the 64 tooth wheel and the 8 tooth pinion.  But I haven't absorbed how he went about getting those numbers.  I like how you explain it.  But I'm going to have to study it a little and play with the numbers till it makes since and I'm a little more automatic with it.  I get the 30 tooth escapement.  60 seconds. 30 teeth. hits the pallet twice.  That's easy...

Thanks for the explanation though.  On the first read it seems much easier to understand than Clayton's way.  I'll keep you posted...

Offline steve323

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Re: Inertia
« Reply #9 on: March 10, 2016, 09:03:09 AM »
Clock designs have always fascinated me.  I had a wind up alarm clock as a kid and used to take it apart just to figure out how it worked.  I have a few books describing clock design and construction.  Most are reprints originally written in the 1800s and early 1900s.  They all describe the same concepts because all clocks are operating on the same basic principles.

I like many of Clayton's designs.  If you spend the time to make the clock by hand, then it should look unusual.  I wouldn't want someone to look at one of my clocks and think that they could buy a similar looking clock at Walmart for $50.

Steve