Choosing the right suspension spring

Discussion in '400-Day & Atmos' started by KurtinSA, Oct 29, 2019.

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  1. KurtinSA

    KurtinSA Registered User
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    I'm not sure I've seen any discussion about why some clocks have two different suspension springs listed in the guide and how one goes about figuring out which one is needed.

    I'm working on a Uhrenfabrick Herr plate 1461B. The existing spring looks suspicious as not being a Horolovar spring...it has a coppery color to it. Plus it's too short, so I need to fit a new one. The guide mentions two spring thicknesses, 0.0035 and 0.0038. I suspect the reason has to do with the pendulum weight but since weights for various clocks is not presented anywhere, it's a guess as to which spring to use. In my case, the pendulum weighs 9.8oz.

    So barring anything else, I'm going to take two uncut lengths of both of these springs and hang the pendulum (without a fork) and record the time it takes for 8 beats. Then I'll use the info Harry put together to scale my rate for the long spring down to the projected rate with the proper length spring. Hopefully this comparison will lead me to select the right spring. I hate cutting springs to fit in a clock only to find that it's not the right spring.

    Kurt
     
  2. MartinM

    MartinM Registered User

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    Not near my Horolovar book, right now but, IIRC, there are two pendulums for that plate one "right hand" (CW) to slow and one "left hand" (CCW) to slow. Not sure from memory, but I think the left hand one is the smaller spring.
     
  3. shutterbug

    shutterbug Moderator
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    They're not expensive. Get one of each :)
     
  4. KurtinSA

    KurtinSA Registered User
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    #4 KurtinSA, Oct 29, 2019
    Last edited: Oct 29, 2019
    shut - You don't know me!! I'd rather make the right choice than start cutting springs.

    Martin - there was a note in the appendix that the regulating nut turning CW to make things go faster requires a 0.0038" spring. I'm not sure what the direction that the regulating nuts turns has to do with anything, unless that signifies a specific weighted pendulum. In my guess, my regulating nut requires a CW turn to go faster.

    That said, I've completed my tests with a 0.0035 and 0.0038 spring. Based upon time measurements uncut and then scaling for the final length spring, the results are:

    - 0.0038" would project to a 52.2 second time for 8 beats when cut to the repair guide length
    - 0.0035" would project to a 56.3 second time for 8 beats when cut to the repair guide length

    So this is counterintuitive to the point Martin raised. It seems that because of the regulating nut direction to increase pendulum speed, I should choose the 0.0038" spring. But my bench tests say that no way will I be able to bring the pendulum into regulation. Seems I should choose the 0.0035, or in fact, choose something thinner yet. Just a rough guess from the above results, seems like I should find a 0.0032" spring.

    Kurt
     
  5. etmb61

    etmb61 Registered User
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    Here's what I would do. Take whatever Horolovar spring you have and mount your bottom block. Clamp the top of the spring from some type of fixture at the proper length for the top block of the clock you are working on. I use an old parts clock with one of the early style suspension brackets so I don't have to cut the spring. Set the pendulum to the middle of its adjustment range, set it in motion, time the beats, and do the math.
     
  6. KurtinSA

    KurtinSA Registered User
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    Eric -

    That's soft of what I did...well I didn't clamp the top block as you suggested...but interesting thing to try. I also tried a 0.0032" spring and ended up with nearly 66 seconds for the predicted rate when cut to the right size. So, I guess I'm going to go with the 0.0035" spring and see how well the predictions are. If the rate is still too fast, then I'll begin to thin to see if I can get it to within range. Hmmm...I think I can see how I can clamp the top block to my fixture with the right amount of spring between the two blocks.

    Kurt
     
  7. KurtinSA

    KurtinSA Registered User
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    I did as Eric suggested. For the 0.0035" spring, the distance between the top and bottom block is essentially what's in the guide. Unfortunately, the time for 8 beats is nearly 55 seconds, in the ball park of my spreadsheet calculations. So, I guess I have to go one or two 0.0001" thinner and see what I get.

    This is strange...the size spring I'm going to end up with is nothing like what's in the guide.

    Kurt
     
  8. MartinM

    MartinM Registered User

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    If turning the nut CW makes the arms expand outward, That's the one the book says is .0038"
     
  9. KurtinSA

    KurtinSA Registered User
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    #9 KurtinSA, Oct 29, 2019
    Last edited: Oct 29, 2019
    Martin -

    According to Appendix 18 #106, turning the rating nut CW results in the pendulum going faster, ie, arms contracting. That would require suspension unit 27B which equates to 0.0038".

    But after several rounds of testing, I've settled on a 0.0034" spring which will need a slight thinning. 8 beats with the 0.0034" is about 59 seconds. I realize that's likely within the capability of the pendulum to correct, but I think I'll just give it a few swipes with my sandpaper just to make things a bit more centered on the pendulum. I don't think I'm doing anything wrong, but this seems to be where I'm at.

    Only thing I can think of, I must not have the right pendulum.

    Kurt
     
  10. etmb61

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    Kurt,

    You got me weighing Herr pendulums. I have six so of course six different weights ranging from 7.45oz. to 11.11oz. and they all look the same.

    Eric
     
  11. KurtinSA

    KurtinSA Registered User
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    Eric -

    I'll post up a picture of my pendulum tomorrow. I have other Herr movements but they are a different plate number...a wide one #1159 as I recall. 1461B is a narrow-ish plate.

    Kurt
     
  12. KurtinSA

    KurtinSA Registered User
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    The pendulum is on the smaller size, not like the full size ones on my other clocks. It is only 2.5 inches high up to the top of the hook.

    Kurt

    UHerrPend1.jpg UHerrPend2.jpg
     
  13. etmb61

    etmb61 Registered User
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    Kurt,

    That pendulum looks like it comes from a small clock.
     
  14. KurtinSA

    KurtinSA Registered User
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    I don't have pictures yet of the case...forgot to do that after buying it. But it looks like this one...still a Herr clock but this one has Euramca stamped on the back. I didn't buy this one when I first saw it...I was just getting started with 400-day clocks and didn't know what I was looking at or if it was worth it. It has a mirrored back which I had removed for the picture. As you can see, there's an extension below the movement to, I guess, allow for a smaller pendulum. A lever underneath moves the cup up and traps the pendulum against the extension.

    Kurt

    Didnotbuy1.jpg Didnotbuy2.jpg
     
  15. etmb61

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    Well that explains some stuff. I would have thought Herr would have used a smaller movement with that pendulum. Now the two suspension sizes listed in the book makes sense.

    Eric
     
  16. KurtinSA

    KurtinSA Registered User
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    Except that the two sizes didn't help me. I ended up using your technique of selecting various spring thicknesses and running them through the top block with the excess sticking out the top. Then I clamped the top block to a piece of wood hung off my bookcase. That let me do the 8-beat tests to find the best spring.

    I also realized that I couldn't tweak the clock settings with the movement inserted in the case since it is hung off the top of the case. So I put together a setup where I can mount the movement in another place and hang the pendulum for testing. It's a bit crude but is working well. At some point, I'll put the motion works on and go through those tests. Presumably, if I can get things to run outside the case, it should run when installed inside the glass.

    Kurt

    UHerrTesting.jpg
     
  17. MartinM

    MartinM Registered User

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    Like I said, I didn't have my guide available and was going with the comments from the thread. Glad you've got it figured out.
     
  18. etmb61

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    Kurt,

    I've run into a similar problems with other clocks I've worked on. There was obviously more variation on the clock manufacturing side that the repair guide's authors could not take into account.

    Eric
     
  19. KurtinSA

    KurtinSA Registered User
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    Made an interesting discover and managed to work my way through the problem. The clock runs very well and finally got around to moving the working movement from the test "stand" inside the case. I had to shorten the suspension spring a bit over what was in the guide. But when I went to try and regulate the time, I found that the adjusting knob would turn all the way up and impinge on the bracket that sticks down, effectively stopping the clock. I guess I had a WTF moment.

    I had noticed before that the only way that the adjustor would work is that it would go all the way slow by pushing down on the center rod to spread the balls out. But when I wanted to go faster, the adjustor would free spin until it hit the bottom of the hook...once it hit the bottom of the hook, then the threads could engage. I didn't think too much about it. I started looking around and noticed a few of my spare pendulums had an e-clip around the pendulum middle stem. Then it hit me...I remembered seeing an e-clip sitting in the bottom of the case but I had no idea what it was for. In looking at the picture of my pendulum and then zoom in a bit on the rear view of the clock I didn't buy a number of years ago, it's clear that the e-clip was missing.

    I fiddled and fiddled and could see that the e-clip needed to fit into a detent on the stem but I couldn't get there. Finally, I found that the stem that the hook screws into would screw out of the middle part of the pendulum. With proper positioning of everything, I got the e-clip on and everything threaded back together. Now the adjustor works like it was supposed to!!!

    Kurt
     
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