Help Seth Thomas 124 Center Shaft/Clutch

Discussion in 'Clock Repair' started by DavidOrDave, Dec 28, 2019.

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  1. DavidOrDave

    DavidOrDave Registered User

    Dec 28, 2019
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    Greetings,

    Thanks to everyone on these forums for providing such useful information and tips on these forums, I appreciate learning from the hard-won experience of others!

    Dave here, a novice to clock repair, but I'm generally pretty good at doing finely detailed work. I have a lot of tools for surface-mount electronics work, and I've been known to make my own parts and tools for various purposes using just a drill press (which I sometimes use as a crude lathe).

    I was given a Seth Thomas Westminster Chime mantel clock with a 124 movement a few years ago. It had been in storage for decades but appeared to be in very nice shape. As received, the chime spring was obviously broken but the clock seemed to run OK. I was quite pleased with myself after having replaced the spring without damaging the clock or breaking my fingers! Upon reassembly the Westminster chimes worked and sounded beautiful.

    Everything else worked until I realized the clock was loosing time and would occasionally get stuck at 5 minutes to the hour. The clock has a strong and regular beat and continued to run while the hands were stuck.

    I decided after reading these and other forums and whatever info I could find, that the problem was a slipping clutch. Sure enough - close examination of the clutch via a surgical magnifying loop revealed the spider spring floating around loosely on the center shaft.

    I found pictures of other center shafts/clutches for other clocks, but none in enough detail of the 124 for me to see how it fits together. Some clocks had pressure held to the spider spring with a washer and pin running through the shaft, but I could not see any such pin in the 124 center shaft. Hard to tell without taking it apart. And take it apart I did.

    IMG_2633.JPG IMG_2635.JPG IMG_2637.JPG


    The first photo shows the center shaft assembly. The retainer (bushing) can be seen floating freely. The spider spring floats around as well when poked. The next shows the wheel, spider spring, and retainer removed from the shaft. Finally, a photo showing measurements of the shaft. There's no washer and pin. Instead, it appears that the shaft is tapered and a brass retainer (bushing) is meant to be tapped into place for a friction fit. The spot labeled "0.101 contact" is about how far I can slide the brass bushing onto the shaft before it starts getting snug.

    I intend to clean up the the parts and remove all oil from the shaft and then to tap the brass retainer back into place until I feel that the clutch is stiff enough. However, how do I know it will hold and that the retainer won't just pop free again? Any advice for how stiff I should attempt to make the clutch?

    If I get this fixed, I'll proceed to clean and oil the other parts. Some of the pivot holes are noticeably worn, but not severely yet. I may try to bush the clock sometime in the future as I gain more experience down the road.

    …Thanks, Dave!
     
  2. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
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    Look carefully and I believe you will find that the little brass collet that holds everything together is cracked. Quite common in this model. It will not get tight because as it is pressed on the crack just expands. Now look again and see there is a small extension on the collet that goes in the spider center to keep things lined up. The proper fix is to make a new collet. You may be able to press a tight bushing on behind the cracked collet to hold it in place. I'll look up some pictures from a recent repair.

    RC
     
  3. DavidOrDave

    DavidOrDave Registered User

    Dec 28, 2019
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    RC, Thank you very much! The collet is indeed cracked. I noticed it after it came out of my ultrasonic cleaner. Don't know how precise a job I can do with my crude tools, but will give it a try.
     
  4. Willie X

    Willie X Registered User

    Feb 9, 2008
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    It's easy to test the hand friction.

    Before the clock is put back together, put the hand on and while holding the part by the 3rd wheel, test the friction. Probably about 2 ounces of pressure would be about right. A little grease is in order at the friction surfaces.

    WIllie X
     
  5. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
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    David, found the old busted collet that I replaced a few weeks ago. Notice the raised part in the center that is necessary to keep the spider from slipping off center. The other picture is the new collet I made in place. Not much shaft left so backing the old part up with a tight bushing won't work. Looks like this would be a very good time to consider a new (or used) lathe. Others here may offer some other "fix", but not only do you need to keep the collet in place, you need to do so while it is under spring tension.

    RC

    DSC06515.jpg DSC06640.JPG
     
    Dave T likes this.
  6. DavidOrDave

    DavidOrDave Registered User

    Dec 28, 2019
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    Thanks very much. Again, much appreciated.

    Not likely to buy a lathe to make this one part. I'll figure something out. Maybe I'll try to do something on my drill press. A 3/32" drill gets me to about 94 mils, then a broach to get to the final ID. I think I can cut the necessary alignment shoulder. I don't see a great need to reproduce the beveled edge so long as the part isn't thick enough to approach the back plate.

    Seems like a silly way to hold things together, but I assume Seth Thomas knew what they were doing (maybe not - since this is said to be a common problem). I like the pin idea better, or a grove and an E washer would work well, I think.

    Anyway, I think I can figure out the correct spring tension as I tap things back together and I suppose it's not very critical, so long as you can still turn the hands without excessive force.

    For now, and now that I know what the problem is, I'm going to clean up the rest of the clock and set it aside until I get the part. I'll send pictures as I make further progress.

    ...Thanks, Dave
     
  7. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
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    I suspect that ST found it faster and easier to just press the parts together. The real issue was apparently a lack of quality control - inferior brass and/or incorrect press fit dimensions. One doesn't buy a screwdriver for a single screw or a lathe to make a single part but with anticipation of many future uses. Good luck

    RC
     
  8. DavidOrDave

    DavidOrDave Registered User

    Dec 28, 2019
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    Greetings,

    Following up on my Seth Thomas 124 repair with the slipping clutch:

    The clutch collet had cracked and would no longer hold the spider spring in place, so the minute hand was slipping. I made a new collet using my drill press as a vertical lathe.

    I started off with a section of 0.25” brass rod and spun it into a undersized drill bit which was fixed in a vice. The hole came out well centered, but somewhat sloppy. I was shooting for 101 mils and used a 5/64" drill (78 mils). I had a ways to go. My first attempt with a 3/32" bit came out over-sized.

    Then I used a set of broaches to enlarge and smooth the hole in order to approach the desired 101 mils (tapered by 1%, as defined by the broach, and probably a good match for the center shaft). I got close to, but not quite at the point where I could insert the center shaft. That's just where I wanted to be.

    I mounted a ground-down, cheap wood drill bit on a small x-y-z stage (surplus) to serve as a cutting tool. The stage let me move the tool around with some precision. I affixed the stages to the drill press and locked everything down.

    I made some test cuts and then turned the rod down to the required outside diameter of 215 mils, and then to the final shape having a shoulder of 122 mils, as needed to keep the spider spring centered. The shoulder was about 18 mils deep. I made a bit of a bevel on the reverse side. But this is largely cosmetic. I decided to leave more material than the original to improve its strength.

    The most critical thing was that the central hole be perfectly sized and finished to provide a good press fit onto the center-shaft. I was happy with the initial broached hole and waited until I was happy with the overall shape of the collet before fine tuning the hole further.

    The centering shoulder and overall thickness are the next most critical dimensions, and I got them really close, better than 1 mil I’m gonna say!

    I finished it and parted the collet from the rod with a final cut into center. I managed not to loose it as it flew off the drill press!

    Then I iteratively used the broach with a light touch, and gradually fitted the collet onto the tapered end of the shaft. I used the tapered broach as a gauge as well, knowing how far the original collet slid up it. I finally polished the hole with Brasso and kabob stick.

    The finish came out amazingly smooth. I think I was probably taking off about 10 thousandths at a time between the broach and the Brasso! I ended up with a perfect fit. I put it all together and tapped the collet into place.

    The photos show the result. This fixed the slipping clutch and amazingly, after cleaning the parts I actually got it all back together, oiled it, fiddled with the adjustments - and it's running!

    I'm quite pleased with my first clock repair (other than immersive cleaning, and poking at and bending things). There is some wear of the pivot holes and I suspect I'll have to attempt to add bushings in the future. But for now, I've spent many hours and I'm ready for a break. I'll let the clock run for a few months or more (if all goes well!).

    Someone previously bent the suspension rod to shorten it, and so, the clock runs fast. I restored the rod and put the clock in beat, and I think its about right. I used Audacity to record the ticktock sound and to look at the waveform timing as I bent the crutch (I'm an electronics engineer, I couldn't resist!) About 34 ms tick to tock. A little more adjusting of the suspension screw adjustment now is in order. But it's close, and seems to be keeping time and chiming away.

    Thanks for your helpful replies to this thread.

    This 1942 Seth Thomas 124 mantel clock is a beautiful thing to behold and enjoy now that it's working properly.







    IMG_2652a side by side.JPG
    Old and new collets
    IMG_2651a both on shaft.JPG
    Both on center shaft for comparison
    IMG_2664a ready to assemble.JPG
    Ready to assemble
    IMG_2667a assembled.JPG
    Final assembly
     
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  9. DavidOrDave

    DavidOrDave Registered User

    Dec 28, 2019
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    Typo: "About 340 ms tick to tock". That's 340 milliseconds.
     
  10. Uhralt

    Uhralt Registered User
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    Very well done with your limited resources!

    Uhralt
     
  11. shutterbug

    shutterbug Moderator
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    Oct 19, 2005
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    I think you're ready for bushings. After that, they should seem pretty easy ;)
     
  12. DavidOrDave

    DavidOrDave Registered User

    Dec 28, 2019
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    Greetings, here's a quick update, several weeks later...

    The clock continues to run reliably and the clutch is working great after several weekly windings, keeping excellent time except - occasionally I get a single strike at the chime warning position. Thereafter, the chime synchronization and hourly strike are delayed by 15 minutes. I can re-synchronize it by moving the hands back to just before the previous 1/4 hour point and then forward again until the correct chime plays. This has happened a couple of times. I suspect I have one of the adjustments slightly out of whack, but am not sure. I'm going to pull the movement back out sometime and watch it closely at the warning positions.

    I bought a dial resilvering kit and plan to do the resilvering soon, but want to get this fixed first. I also ordered bushings. I plan to rebush it within the next six months or so as time permits.
     
  13. shutterbug

    shutterbug Moderator
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    The strike is either not completing or is stopping with the hammer raised. Look at that, too.
     
  14. DavidOrDave

    DavidOrDave Registered User

    Dec 28, 2019
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    Thanks, shutterbug. I'll see what I can find...
     

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