Making a new mainspring barrel question

Discussion in 'Clock Repair' started by Harry Hopkins, Mar 14, 2019.

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  1. Harry Hopkins

    Harry Hopkins Registered User
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    A customer sent me a small mainspring barrel out of a Junghans Swinger clock for me to duplicate. At some point nearly a third of the teeth had been broken off and been repaired. The repair had since failed also when the mainspring had broken into 4 pieces. He wanted a new barrel and not a repair. The mainspring is a 'hook' end and it is supposed to hook onto the barrel where the sleeve has been pierced (see pics). I have completed the barrel but I have no idea how to make this spring hook and don't want to do anything that will destroy my work. I am leaning toward installing a conventional barrel hook and cutting off the end of the mainspring and making it a 'hole' end mainspring. I would like to hear how others would proceed with this.

    Junghans barrel 2.jpg
    See hook at top of picture

    junghans barrel.jpg
    See hook at bottom of old barrel
     
  2. Les Sanders

    Les Sanders Registered User
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    I have used this video several times it works great.

     
  3. Harry Hopkins

    Harry Hopkins Registered User
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    Thanks for the video Les.

    I was hoping to find a way to put a hook in the new barrel sleeve similar to the original hook so I could use the 'hook end' mainspring that is original to this Junghans Swinger.
     
  4. R. Croswell

    R. Croswell Registered User

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    I would install a new spring hook as shown in the video and use a hole-end spring.

    RC
     
  5. shutterbug

    shutterbug Moderator
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    I agree. It's a much stronger repair than the raised portion of brass would be.
     
  6. Jerry Kieffer

    Jerry Kieffer Registered User
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    Hey Harry
    You did not ask the question in class, or did the instructor screw up and not cover it ??

    You can of course machine interior support and punch it as it was originally done, but I suspect you would not want to go through this much work, so I will not elaborate unless requested.

    Actually its quite simple since you have a milling machine. You can machine a "U" in the barrel with a .020" four flute endmill, just go slow. Four Flute endmills can handle more stress than two flute. While what you have done will be quite obvious when complete, but the endmill path will visually disappear when the section is bent.

    Good Luck
    Jerry Kieffer
     
  7. Harry Hopkins

    Harry Hopkins Registered User
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    RC and Shutterbug, Thanks for the info. I have emailed the clocks owner to see if he has a preference.

    Hey Jerry, I'm pretty sure it was an instructor screw up :chuckling:. (or maybe I took an afternoon nap). Thanks for the info about making this hook. I checked the prices of .020" quality 4 flute end mills... Not in my budget for this job unless the clock owner insists on a barrel to exactly match the original.
     
  8. David S

    David S Registered User
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    Harry I am a bit late to this party, but I have been searching for pictures of a hook I made in a Hermle barrel some time ago. I finally found it, but perhaps too late.

    The process was to layout the hook on the barrel, drill starter holes and cut the "U" with a fabricated piercing saw. The entire process took about an hour as I recall. I drilled 4 holes in the corners of the hook, but in the future I would only drill two for blade starting holes and also to reduce stress concentrations at the bend area.

    The "Saw" was made out of some stiff but bendable steel rod flattened at the ends with a slit cut in. The piercing saw blades were simply soft soldered in place once the blade was threaded through the starter hole.

    The blade is soldered at the bottom but not at the top yet.
    piercing saw top not soldered.jpg the saw is tentioned with the wire shown and top soldered soldering top blade support.jpg

    piercing saw set up.jpg sawing inside close.jpg and final prior to clean up complete hook inside.jpg

    David
     
  9. Harry Hopkins

    Harry Hopkins Registered User
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    David, Thank you for the detailed method and pictures... a very ingenious way to make the hook I was needing. Many times I have spent more time making a tool for a job or designing a way to hold work in the mill than it takes to accomplish the job. I would guess your homemade jewelers saw falls in that category. It is also a reminder that there is always more than one way to do a task.

    The gentleman that I made the barrel for told me to do the job with whatever method used less labor so I machined a traditional barrel hook and riveted it in earlier today.
    image000000 (86).jpg
    New barrel and hook
    image000000 (85).jpg
    Hook riveted in barrel
    image000000 (87).jpg
    New barrel and new mainspring with original cap and arbor.
     
    etmb61 likes this.
  10. David S

    David S Registered User
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    Nice going Harry, it looks great. Well actually the entire job you did is very nice indeed.

    Regarding time. Yes it is sort of the 80 / 20 rule sometimes. 80% of the time is set up and prep, 20% making chips. I actually wanted to try it this way since the smallest end mill I had was Ø 1/32", and that would have been too much "air" around the tang. Also what happens when folks starting out don't have a mill. The kerf was only 0.010" wide so looked fairly close to the original from that respect. What surprised me was how little time it took to make the cuts considering the relatively short stroke.

    David
     
  11. etmb61

    etmb61 Registered User
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    Beautiful work Harry!

    Eric
     
  12. Harry Hopkins

    Harry Hopkins Registered User
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    Thanks David and Eric. It was a fun project.

    David, I was looking at your pictures again for future reference and I noticed that in the picture where you have the barrel in the vice there is already a tang at the bottom of the barrel opposite where you are making another one.. Why did you need an extra tang?
     
  13. David S

    David S Registered User
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    Harry, Yes indeed, a good eye.. The bottom one was cracked, and just like so many discussions on this forum I was considering if I could silver braze it or not. Actually there is a pic of butane torch in one of the photos that I had brought out. I was concerned about what the heat would do even though I thought that I could get enough heat into the tang without do doing too much damage else where, but didn't think I could get the crack clean. So I left it to see how making a new one would work out. In the end I removed the cracked piece and flattened the rest.

    David
     

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