Understanding behind-the-dial mechanism

Discussion in 'Tower, Monumental & Street Clocks' started by focusrsh_b07732, Jun 2, 2020.

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  1. focusrsh_b07732

    focusrsh_b07732 Registered User
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    Dec 17, 2009
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    I am a complete beginner at anything related to public time clocks, so please excuse what probably are some "duh" questions.

    Last year at the Chattanooga NAWCC mart, I bought the remains of large clock. It clearly was meant to drive a dial remote to it, since there is a bevel drive coming up out the top.

    So the question: Since only a single shaft goes out the top, presumably the minute drive, is there a 12:1 reduction gear behind the remote dial to drive the hour hand, just as there is in many inexpensive small clocks? I've never seen the behind-the-dial mechanism for a clock with a remote dial. Can someone post some photos?

    I'll have to machine everything from scratch, which isn't a problem. I do have lots of experience restoring smaller clocks, everything from Ansonia kitchen clocks to a Synchronome, and have plenty of large and small shop tools, lathes, vertical mill, etc., but it would be nice to see what has been done before and not reinvent the wheel. (And reinvent all the mistakes, too.)

    Unless...

    Anyone have a dial and associated parts? My goal is to install this clock with the public face on the outside of my shop, so something maybe 18 inches across would be about the right size.

    Thanks,
    Carl Dreher

    IMG_6358.JPG IMG_6375.JPG
     
  2. FDelGreco

    FDelGreco Registered User
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    Carl:

    The mechanism behind the dial is called the motion works. Shown below are three views of the motion works I have for a German tower clock. In the first view, power comes from the clock into the right side and passes straight through to the minute hand. The arm hanging off of it is the counter balance used to balance the weight of the long minute hand so it doesn't always want to point down. The minute shaft also turns a 39 tooth gear just to the left of the mounting bracket. It meshes with another 39 tooth gear -- the purpose is simply to get the lantern pinion that is attached to that gear far away enough from the center shaft to mesh with the big gear that is attached to the hour pipe -- a tube. The pinion has six teeth and the big gear has 72, thereby providing a 12:1 reduction for the hour hand. Note that some motion works accomplishes the reduction in two steps, rather than one like this one.

    Frank

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  3. PatH

    PatH Registered User
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    Just curious....what is the height of this movement? Thanks!
     
  4. focusrsh_b07732

    focusrsh_b07732 Registered User
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    #4 focusrsh_b07732, Jun 2, 2020
    Last edited: Jun 2, 2020
    13 inches square and 7.5 inches deep.
     
  5. focusrsh_b07732

    focusrsh_b07732 Registered User
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    Dec 17, 2009
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    Hi Frank,
    Thanks, that helps a lot! Looks very straight forward.
    I'll need construct a 90-degree drive because the power come out the top of the movement. (Or just buy a commercial angle gear unit.) I think I'll have to pay close attention to friction, since the movement, not being very large, probably doesn't have a surfeit of power.
    This will be an interesting project!
     
  6. focusrsh_b07732

    focusrsh_b07732 Registered User
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    Here's a couple of more pics. There are no marks anywhere on the movement indicating the maker.

    IMG_6389.JPG IMG_6368.JPG
     
  7. FDelGreco

    FDelGreco Registered User
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    Carl:

    Yes, you'll need one or more right angle drives. Shown below in images 1 and 2 are 90 and 45 degree bevel gear sets for the same German tower clock -- admittedly dirty as I haven't used them yet. Image 3 is a bevel gear all cleaned up. Image 4 is a bevel set from the museum's Ansonia street clock, showing that these sets come in all shapes and sizes. You could machine a set yourself if you are quite competent with cutting gears (I'm not). There was an article in the Bulletin several years back describing the process. Or for your clock, since it is fairly small, you might use a right angle drive for an RC car. You can find a ton of them reasonably priced with a google search -- either the whole thing built or just the individual gears -- metal or plastic.

    You'll notice in images 1 & 2 that there are universal joints hanging off the ends of the sets. These allow for slight misalignments between the bevel set and the motion works, or between the clock and the bevel set.

    Frank

    right angle bevel gears.jpg 45 bevels.jpg bevel gear.jpg ansonia bevel.jpg
     
  8. focusrsh_b07732

    focusrsh_b07732 Registered User
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    Frank-
    I've looked at the bevel gears sold by Servo City (ServoCity.com - Servos, Actobotics, Gears, Motors and More!), and they look like off-the-shelf items for rigging the dial.
    One problem I am faced with is the missing bevel gear inside the works. I've circled where it is suppose to be in the photo. Its mate is also shown. I could, of course, get a matching set of modern gears and replace both of them, but I hate to do that to the clock when the original part is there. Feels like cheating.
    I've never tried cutting a bevel gear. Maybe it is time to learn how.

    missing bevel gear.JPG bevel gear 2.JPG
     
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  9. Jim DuBois

    Jim DuBois Registered User
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    Cutting a bevel gear for a clock motion works is not all that difficult. Just like a conventional wheel, but done at an angle. Now, if one wanted to cut a bevel gear to modern specifications it becomes more difficult, but that is not necessary for our purposes. I have cut quite a few using the loose approach as mentioned above. I used cycloidal cutters as that was what was used with some other bevel gears in these clocks. I have also used modern involute cutters but prefer the old style. You will notice the tooth thickness varies from front to back on the gears made this way. For our purposes that is fine. If you were machining them for high speed power transfer you might want to be more precise with your angles and maybe make multiple passes, but not needed here.

    IM000388.JPG IM000399.JPG 2013-10-28 08.24.23.jpg
     
  10. FDelGreco

    FDelGreco Registered User
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    Quite a few years ago when I was the editor of the tower clock chapter newsletter, a member sent me an article he wrote on how to cut bevel gears. Since he also sent it to the Bulletin editor for inclusion in the Bulletin, I didn't publish it. But here it is now.

    Frank
     

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  11. focusrsh_b07732

    focusrsh_b07732 Registered User
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    Frank, thanks for the article. Looks pretty challenging to me.
     
  12. scootermcrad

    scootermcrad Registered User
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    Neat little clock! Great find! Looks like maybe the wheels, arbors, and maybe side plates, etc. were from another clock and a new body was built to carry it all, or do we think this is original? You may need to check the output timing of the assumed "minute arbor" as it may have originally accounted for a speed change in the bevel set before getting to the further reduced motion works. Many bevel sets had their own ratio before connecting to the lead-off shafts that connected to the motion works. I've heard this is often to prevent binding on bevel gears with cycloidal cut teeth, but I am still trying to get the real facts behind that statement. Maybe Frank or Jim can tell us more about that.

    Great article, Frank! Thank you for sharing! I actually have some of that work to do for some projects. That is helpful!
     
  13. scootermcrad

    scootermcrad Registered User
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    #13 scootermcrad, Jun 12, 2020
    Last edited: Jun 12, 2020
    Here are a couple more pictures of motion-works from a Seth Thomas installation. The dirty before with a mounting arrangement intended for a wood dial but rigged for a glass dial (ultimately undone) and restored with the correct collar and face nut for a glass dial. Maybe this will give you some ideas.

    Also, so clues to the make of your clock may be the wheels themselves. I see some five spoke wheels. Might be the first place to start looking. I have a French Turret clock with all 5-spoke brass wheels similar to yours, but no solid wheels. So maybe start looking at European makes. I'm sure there were many American clocks with 5 spokes as well, though.

    EDIT: Looking back at some photos, it seems Howard street clock movements this size had 5 spoke wheels, also. So definitely many makes to consider. Maybe those pieces of the side plates that carry everything are the clues, as well as the pendulum with the dog leg.

    IMG_8156.JPG IMG_2378.JPG
     
  14. scootermcrad

    scootermcrad Registered User
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    And here is a dirty ol' set of bevels that connect to lead-off shafts. Also Seth Thomas.

    IMG_2379.JPG
     
  15. scootermcrad

    scootermcrad Registered User
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    One more of this Seth Thomas showing how all of that connects to the the movement with another bevel, which is a horizontal output.

    IMG_2361.JPG
     

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