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Other escapements / Re: Continuous motion escapements, Conical pendulum clock
« Last post by steve323 on April 10, 2014, 11:18:22 PM »
I thought about this some more and here are some comments:

Consider a clock with a 39" pendulum and 30 tooth escapement.  The escapement will rotate once every 60 seconds.  This will need to be divided down by 60 for the minute hand.  It will need to divided down again by 12 for the hour hand.

Compare this to a 39" conical pendulum.  The drive mechanism will rotate once every 2 seconds.  This needs to be divided down by 1800 for the minute hand.  The divide by 12 for the hour hand is identical.  One difference between an oscillating pendulum and a conical pendulum is that the fastest wheel needs to be driven 30 times faster with the conical pendulum.  This is the difference between an escapement rotating every 60 seconds vs a drive mechanism rotating every 2 seconds with a conical pendulum.

It appears that the start/stop characteristic of the escapement gets replaced by 2 sets of wheels to speed up the "escapement" by 30X.  My guess is that this might be about equal from a mechanical efficiency perspective.  One advantage of the conical pendulum is its near silent operation.  This is great for a bedroom clock.

I want to build one, just as soon as I can finish a few of the other projects on my list.  :)

Steve
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Other escapements / Re: Continuous motion escapements, Conical pendulum clock
« Last post by steve323 on April 09, 2014, 09:17:53 PM »
The first video of the Farcot clock looks very promising.  It appears to have the same regulating accuracy as a standard oscillating pendulum.  It seems like the start/stop motion of the escapement would be completely eliminated and it should require significantly less weight to drive the clock.  The most sensitive part of a clock is probably be the escapement.  This design replaces the escapement with a continuous rotary motion.

A few aspects would make a clock differ from a traditional clock.  All of the wheels are below the pendulum and the first stage rotates vertically.  The clock face needs to be horizontal, so one pair of wheels needs to be at 90 degrees.  The clock face is typically above the pendulum, but this is easily fixed by using shaft to the top.  The video shows another interesting option to use a statue of a person holding the pendulum and keep everything else at the bottom. 


I suspect that the fly fan and centrifugal governor would not work well as a clock.  A fly fan would be very sensitive to air density, so the speed would change based on barometric pressure in addition to being sensitive to the driven weight.  It is acceptable for regulating the chimes, since a small change in the time between notes is OK.  A centrifugal governor seems like a poor regulator.

Steve
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General Discussion / Re: Thomas Clock build
« Last post by Rocketcaver on February 25, 2014, 04:48:57 PM »
Inspection of my newly cut gear revealed that the actual dimensions don't match those shown on the pattern.
Drat!
Obviously I should have checked before I cut the gear.  Oh well, it was good practice.
Looking over my printer settings, I find that when printing PDF's it defaults to "shrink to fit".  Setting it back to "actual size" fixes the issue, but then of course some parts are too big to fit on an 8 1/2" X 11" sheet.  Luckily I can print 11" X 17" sheets, that should fix the problem.  I'll try that this afternoon.
What's that they always say about "measure twice and cut once"?
I freely admit this stupid newbie type mistake on my part so any other beginners who might stumble across this thread might be forewarned.
Still, it was only one gear.  I had a lot of fun making it, and learned several things in the process.  I think I'll go ahead and finish it out and pretty it up and make a wall hanging out of it.

Later...

Yep, the 11X17 set to "actual size" did the trick.


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General Discussion / Thomas Clock build
« Last post by Rocketcaver on February 25, 2014, 03:21:39 AM »
Let's start with some background.
Somewhere around 1990 or so, I ordered the Thomas Clock plans from an ad in the back of some magazine.  I received a set of large folded up plans with an assortment of very intimedating looking gears and other pieces.  The plans went into a drawer and didn't see the light of day again for many years.
Somewhere around 2010 or so I came across those plans again.  They were a bit ragged around the folds from being shuffled around over several moves and several other "filing systems".  My interest renewed, I found the company who originated the plans online and emailed them asking if the plans had been updated as I was once more interested in building the clock.  I received back a very nice email with a PDF attachment containing the revised version of the plans.  It seems that the old original plans had been drawn by hand, the new version had been recreated using CAD, and a few minor issues had been corrected.  The parts were all nicely arranged logically on 8 1/2 X 11 sheets for full scale print out.
Life happened and a few more years passed.  Now, at long last, I am ready to start building this clock.
I have made a bit of a start already, over the last couple of nights I have cut out one of the bigger gears.  Not being a wood worker at all, this has been a challenge, and a lot of fun.  I cut the teeth on the bandsaw, and cut out the spokes on the new scroll saw... my first scroll saw project!  I was able to repair a dumspter-found disc sander, so I used that to dress the ends of the teeth, and in a few days I should receive a new (cheap) 1" belt sander to true up the faces of the teeth.  One might think that the whole project was just an excuse to buy a bunch of new tools.  I might have to think ponder that one for a while.
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General Discussion / Re: Genesis Clock build
« Last post by Rocketcaver on February 25, 2014, 02:40:59 AM »
I have hit a minor, or major, snag in this project.
Looking through the plans and looking at my collection of materials, I find that what I thought was my stock of 3/8" BB plywood is in fact 1/2" BB plywood.  I had it in my head that the old Thomas Clock used 3/8, but digging the plans back out it does call for 1/2", which accounts for my stock.  So, in order to keep from having to order more materials I'm going to shelve the Genesis Clock for a while and start on the Thomas clock.
I'll start another thread for that to keep the two projects seperate.
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Other escapements / Continuous motion escapements, Conical pendulum clock
« Last post by mackerm on February 22, 2014, 04:20:08 AM »
I've become convinced that continuous-motion escapements are especially suited for wooden works clocks. The main reason is that the escapements can occasionally pull on the gear train, in addition to being pushed by it. This should make the clocks naturally tolerant of sticky spots on the teeth. It should also allow the clocks to work with much lighter driving weights.

Let me start by saying that conical pendulum clocks of the type made by Farcot seem like the best solution. They also happen to be things of beauty:
http://youtu.be/QO_oUpGRSGc

First, though, I want to mention a couple other devices.

Fly Fans

Nobody will argue that fly-fans are the ideal heart for a precision timepiece, but they are a good proof-of-concept. I've done a lot of looking, and find that fly fans have been used to control the speed of various mechanical devices, including lighthouse lenses. In clocks, they are commonly used to control the chimes, where the repeated start-stop action can cause wear and breakage. But if the fans are allowed to turn continuously, that liability becomes an asset. The fan's mass can pull on the train, making poorly balanced and rough wheels functional.
http://www.youtube.com/watch?v=bJhIGWiMwwg

If my memory is right, air drag is proportional to the square of speed, which means that if you want to double the speed of a fly fan, you'd make the weights four times heavier.

Brake-type Centrifugal Governors

Also known as Centrifugal Brakes, these devices control various light-duty machines, such as movie cameras, rotary telephone dials and wind-up phonographs:
http://www.youtube.com/watch?v=7bfzLoHiXTk
http://www.youtube.com/watch?v=aB2AWckXCgE
http://www.youtube.com/watch?v=8ye2Bj6reEc

I've also found these in lighthouse mechanisms. But they are also used in clock drives for telescopes, which need to be exquisitely precise to make time exposures. It's therefore puzzling that they are seldom used in plain old clocks.

I can think of one possible disadvantage: the speed of these devices is much greater than the escape wheels in clocks with pallets. This implies that you'd need to have an extra wheel and pinion. Ordinarily, you'd expect an extra wheel to multiply the friction load, but as I've been hammering here, continuous-motion clocks should have naturally low friction. Another benefit: the weights don't have to accelerate the gear train after every pendulum swing.

Conical pendulum clocks

Besides the Farcot clocks, a well-known brand is the Briggs Rotary Clock. The Farcot ones correctly keep the pendulum at a small angle to the vertical, while the Briggs ones seem to have an uncomfortably large swing. There is one variation which is critical to putting them in a wooden works clock. Usually, the bottom end of the pendulum rod rests against a horizontal arm which rotates, but sometimes this arm is replaced with a two-tined fork. The two-tine arrangement will allow the weight of the pendulum to occasionally pull on the train.

I'm not a woodworker, but I'm eager to read what people think about these mechanisms. (They're not even usually called escapements, but I can't see a better term.)

I'd also like to know if I'm right that replacing the pallets with a heavy fly-fan would allow much lighter driving weights. If it works, it would allow beginners to make a clock that actually works, and would free experts to spend their efforts making interesting complications.
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General Discussion / Re: Genesis Clock build
« Last post by jasc15 on February 21, 2014, 03:26:45 AM »
Good luck.  I'm interested to see your progress.

I have this forum in my RSS feed, so I see all new posts, including the spam posts.
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General Discussion / Re: Genesis Clock build
« Last post by Rocketcaver on February 21, 2014, 02:10:27 AM »
Thanks for the comment Josef.  Yes, the forum has been pretty quiet for a while.  As long as I know at least one person is following along I'll keep up with updates.
Looking over these clock plans, I realize that I got lucky in at least one respect.  This clock uses mostly 3/8 plywood... I still have most of the 3/8 inch Baltic Birch plywood that I ordered a couple of years ago, and I have plenty of brass stock and drill rod (silver steel) for the arbors so I'll just have to buy a few bits and pieces.  I'll have to do some shopping this weekend and pick up some scrollsaw blades though, kind of hard to get started without those.  Any advice on what blades to get would be welcome.
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General Discussion / Re: Genesis Clock build
« Last post by Sablatnic on February 20, 2014, 08:23:56 PM »
Congratulations on your new saw, And I will be looking forward to seeing the progress on your clock! But don't expect too many comments. We are quite a quiet bunch of people here.

Josef
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General Discussion / Genesis Clock build
« Last post by Rocketcaver on February 20, 2014, 05:20:23 PM »
I received my new scroll saw yesterday, as well as the Spring 2011 edition of ScrollSaw Woodworking and Crafts Magazine (issue #42).  This issue has the plans and a very nice write-up for Clayton Boyer's Genesis Clock, which is touted as a simple to build and get going affair suitable for the beginner.  As I am a complete beginner at this sort of thing, I thought it would be a good place to start.  I am sure that "simple" is a very subjective term.
I thought I would start a build thread here to document my progress.  I invite all comments and suggestions; I have the feeling that I will be able to use all the help that I can get.  I'll add photos as I progress.


 
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