340-020 Options NB vs Bronze

Discussion in 'Clock Repair' started by MuensterMann, Aug 14, 2019 at 4:45 PM.

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  1. MuensterMann

    MuensterMann Registered User

    Mar 23, 2008
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    If replacing a 340-020, there are two options: NB and Bronze. What is the difference in terms of quality? Does one have a bronze bushing on the 2nd wheel and the other one (NB) has brass? Thanks!
     
  2. wow

    wow Registered User
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    Bronze is a little harder. Supposed to last longer. I usually use bronze on very worn holes (oblong). Especially the second wheel.
     
  3. MuensterMann

    MuensterMann Registered User

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    What is the difference of the two when buying new movements?
     
  4. bruce linde

    bruce linde Technical Admin
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    i know there are other threads on the merits of bronze vs. brass... but aren't bronze bushings harder on pivots? causing more wear?
     
  5. MuensterMann

    MuensterMann Registered User

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    There are two models of the 340-020, one has bushings in the 2nd wheels and the other one does not (the one marked "NB", perhaps for No Bushing). So, if it doesn't have a bushing, then what does it have? The NB is about $21 cheaper. Perhaps bronze does not play into my question.
     
  6. R&A

    R&A Registered User

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    Perhaps NB means..... NOT Bronze
     
  7. Fred Reiss

    Fred Reiss Registered User
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    I give the customer the option. Bronze is supposed to last longer, but I tell them either movement will outlast me...lol.
     
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  8. glenhead

    glenhead Registered User
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    NB = not bushed. NB is cheaper because the bushed one took the extra effort of doing the bushing.

    Yes, bearing bronze (Rockwell B 65.8) is harder than cartridge or engraver's brass (average Rockwell B 48). They're both softer than steel (Rockwell B 71). Dirt and dust will embed into the surface of a brass bushing more readily than bronze, and dirt and dust embedded in the bearing surface is what causes wear on steel pivots. All in all bronze outperforms brass.

    All that said, in a well-maintained clock either one will last a heckuva long time. Unfortunately, 99% of the time "well-maintained clock" is an oxymoron...

    Glen
     
  9. MuensterMann

    MuensterMann Registered User

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    So, for the one that is more expensive, since a bushing was added, what is so special about this movement? Is it because the bushing is bronze - and the NB one just has a hole cut out of the brass plate?
     
  10. R. Croswell

    R. Croswell Registered User

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    Interesting that this movement is offered in bushed and non-bushed versions. I could not find on the Black Forest Imports site any specific information of whether the bushings are bronze or brass, although I see no reason to put brass bushings in a new brass plate. Is the non-bushed version still being made or are they remaining new old stock?

    As for brass vs bronze, I've seen a lot of brass clocks where the original brass pivot holes lasted 100+ years so brass has a pretty good record when properly maintained. I've used some bronze bushings years ago and never had any problems but also never saw any significant advantage. Perhaps bronze has an advantage on heavily loaded 2nd wheel pivots, especially with hard pivots. Now I try to bush/rebush with brass or broinze according to what the manufacturer originally used.

    I agree completely.

    RC
     
  11. MuensterMann

    MuensterMann Registered User

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    What does a well-maintained clock entail? Perhaps a standard maintenance would be every 5 years disassemble the movement, clean, assemble, freshly lubricate.
     
  12. R. Croswell

    R. Croswell Registered User

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    Good question, difficult answer. Some clock makers (old and modern) specified oiling intervals and/or cleaning intervals, but I think it depends of the clock and the environment where it lives. Also the type of oil used. Well maintained to me means oiling frequently enough that the pivots never go dry and cleaning often enough to prevent an accumulation of dirt and goo. At today's shop rates if one has to pay to have a clock service it most likely will not be well maintained. Reoil every 3 to 5 years and disassemble and clean every 10-15 years would seem to be reasonable. If the clock noticeably changes its behavior - runs slow, runs down before the rated number of days, occasionally fails to strike, etc, then it may be overdue for maintenance.

    RC
     
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  13. glenhead

    glenhead Registered User
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    yes
     
  14. Time After Time

    Time After Time Registered User
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    I have a theory that in a clean environment, bronze will outlast brass.

    If you introduce dust or other contaminants, I think that brass will out perform bronze and be gentler on the steel pivots because it will allow the contaminants to more easily and deeply embed themselves in the brass. With a lower profile, so to speak, the contaminants will not do as much damage to the pivot steel. Once roughened, the steel abrades the bushing more rapidly and you end up with a cycling. Taken to an extreme, I don't think that steel pivots would hold up very well against a Jeweled bushing if contaminants are introduced. It's just a theory based on what I've read. I don't have any Scanning Electron Microscope Photographs to share.

    As has been said, all of this assumes that the movement will get maintenance before it grinds to a halt. Without maintenance, it's just a matter of time and the degree of repair needed if or when the clock finally does come in.

    Bruce
     
  15. Uhralt

    Uhralt Registered User
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    I know the following is all theory, but....
    If the abrasive material is imbedded in the bushing and grinds away the pivot, wouldn't the pivot wear but the bushing be rather undisturbed? Now, since the bushing still looks good (no ovality) the pivot might be replaced and installed back into the same bushing. It will start grinding right away....

    I guess some prospective long-term studies would be needed to show advantages or disadvantages.

    Uhralt
     
  16. kinsler33

    kinsler33 Registered User

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    There are indeed studies, but none on clocks. The theory is that the brass will grab abrasive dust and act as a lap to grind away the steel, and that's how it works in high-speed engines and gear boxes. But badly worn pivots are rare in clocks: it's the hole that wears out, and not all the holes at that. And if anyone is doing useful research on this, they've had no luck. Photographs with scanning electron microscopes have been done on clock bearings, but I don't believe that there have been any publishable results. I'd like to know the wear mechanisms too, but I've seen nothing but anecdotal evidence (I've generated plenty of that myself) or theories that really can't be supported without running a controlled experiment for the next fifty years.

    If it's of any comfort, research on slow deterioration and wear is of great concern in many fields. Nobody really knows how silicon semiconductor chips will age, or many structural plastic compounds. (I did a good business replacing expensive loudspeakers that had been made with urethane plastic suspensions. They all fell apart without warning in the space of a few years. Urethane drive belts did the same.)

    The only badly-worn pivots I've seen have been in steel-on-steel bearings, as in the Ingraham steel-plate kitchen clock I've been restoring.

    Mark Kinsler
     
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  17. bkerr

    bkerr Registered User
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    worn pivot.jpg worn pivot closer.jpg

    When I first started quite a few years ago now it was had to understand that the steel would wear quicker than the brass. With a bit more experience and information on this board it all makes sense. Much like sandpaper those abrasive grains are held in place and work until they wear out or get torn away from the bond. I the clock the it brass becomes the bond. Dirt (abrasive) if not removed will eat up the steel. Think of a shovel in the dirt, it might start out rusty but after several shovels it becomes bright metal. I attached a pic as an example of a repair that I did some time ago. This clock was "maintained" and because the springs (American clock) were so strong it ate up the steel. Interestingly the plate was not that bad. Still required a bushing and of course a new pivot. Look at the color of that wheel, it was a mess!
     
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  18. bkerr

    bkerr Registered User
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    NOT MAINTAINED
     
  19. Time After Time

    Time After Time Registered User
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    #19 Time After Time, Aug 16, 2019 at 7:50 AM
    Last edited: Aug 16, 2019 at 8:10 AM
    My opinions on these matters have been informed by information originally shared by David S.

    One was an article published in the NAWCC Bulletin by John Losch. He described the process as the "Cycle of Life Wear"

    The Cycle of Life Wear on pallets and in bearings represents a cycle. It has been viewed traditionally that the wear on steel at first exceeds the wear on softer brass, but eventually the condition reverses, then reaches equilibrium until the clock, in these considerations, will no longer run. Abrasive dirt becomes embedded in both escape wheel teeth (at the points), and in the contact point within a clock train bearing. The embedded dirt abrades or laps the steel until the surface of the steel becomes sufficiently rough to file the softer surface.

    Mr. Losch describes what he believes is the "embedded" abrasive mechanisms in brass vs. bronze and suggests that abrasives do not embed as deeply in the harder bronze bushing material. As a result, they present a coarser surface when dirt or any other abrasives are introduced into the bearing. As I understand what he wrote, his evidence is anecdotal experience (both his and others) with bronze bushings.

    You can find a pretty decent discussion on embedded abrasives and attempts to remove it through pegging within this thread: When pegging is not good enough!

    The other source that David provided was a paper titled "CAST COPPER ALLOY SLEEVE BEARINGS" by an organization calling itself the Copper Development Association. In discussing wear mechanisms found in Boundry Lubrication situations, the authors mention contact between Asperities, which break off and lead to wear debris. This wear mechanism is accelerated with the introduction of external abrasives (like dust and dirt).

    https://www.copper.org/publications/pub_list/pdf/sleevebearing_a1063_06.pdf

    The only one I'm aware of is study entitled "An Analysis of Two Pivot Polishing Techniques" By Robert Whiteman, 2008
    https://www.abouttime-clockmaking.com/downloads/Whiteman Pivot Analysis 2.pdf

    I've seen pivots in badly punched pivot holes which were so worn as to require replacement. I've also run across a back pivot on an Ansonia Open Escapement Escape Wheel Arbor. The pivot hole was located in a cock positioned between the plates. I'm guessing that it may have been missed when it was time to oil (or re-oil) the movement. It too was so badly worn that it required a new pivot. Both of these examples were Steel Pivots on Brass Plates. Of course there are many examples of significantly scored pivots which could be refinished, polished and burnished before being put back into service. Almost certainly the restored pivots required new bushings to properly fit their reduced diameters.

    Regards,

    Bruce

    Worn Pivot.jpg P1010302.JPG Repivot1.jpg

    Once again, I think that if you can keep the movement clean and and properly lubricated, bronze bushings in high load areas could be a good way to go. Under those conditions, brass should work pretty well too I suspect. Certainly I agree with RC that if the movement was designed to use bronze bushings in certain areas, one should stay with that design when servicing the movement.
     
  20. mauleg

    mauleg Registered User
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    One more piece of anecdotal evidence:

    One thing that Bruce mentioned earlier in this thread was jeweled bearings. In addition to clocks, I have and maintain a decent-sized collection of pocket watches, most of which I've restored to service and all of which are fully jeweled. Pivot wear on these watches is relatively unusual, I'd say even rare, even in cases (pun intended) where the watch has been run while pretty filthy. This implies that the absence of embedded particles in a harder bearing surface contributes to reduced wear in the pivot. I've also noted that pivots in jeweled bearings on clocks typically show very little, if any wear.
     
  21. R. Croswell

    R. Croswell Registered User

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    We keep hearing about abrasive dirt particles embedded in the bushing or pivot but nothing about abrasive particles suspended in the oil. I rather suspect that is a part of the problem. Also unknown, at least to me, is whether the ability abrasive dirt particles to become embedded can be reduced by oil. Then there is wear and roughing up surfaces resulting from dry metal to metal contact in the absence of abrasive "dirt". Most of the worn pivot holes that I see go along with pivots that have surface damage.

    RC
     
  22. MuensterMann

    MuensterMann Registered User

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    The oiling of a movement every so often, without cleaning, may be a bad thing. The original oil will attract dirt and then the adding of more oil on top of that may distribute the dirt in the oil volume. I used to always add oil/grease to my bicycle chain without cleaning it first - and it seemed good at first, but in the long run it was not good at all. A significant accumulation of oil and dirt layers! Now before adding any oil to the chain, the chain is cleaned first.

    Thus, I believe maintaining a clock should always be a periodic cleaning and fresh oil - as opposed to just adding oil at anytime in the life of the clock.
     
  23. Time After Time

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    #23 Time After Time, Aug 16, 2019 at 1:23 PM
    Last edited: Aug 16, 2019 at 1:57 PM
    I don't know very much about watches or jeweled movements other than that they are usually very well sealed against outside contamination. I think that it should go without saying that a clean jeweled bearing will experience less wear than a dirty one. If you don't see much wear I would have to guess that it's probably because there isn't much wear debris (loose jewel or steel particles). Perhaps one of our Watch cousins from the other side will weigh in and add to your observations mauleg. It might be that one really needs microscopic examination to see any differences.

    Edit: Within the Message Board, this is what I found on the subject mauleg:

    The jewel experiences very little wear because it is so hard, unless the watch has been run for a very long time without cleaning. Dirt and grit cannot embed into the jewel, causing less wear on the steel pivot. Pocket Watch Jewels

    In the case of brass vs. bronze, I think bronze is still soft enough that abrasives can and will embed, just not as deeply. Also, loose bronze particles will be harder than loose brass particles (wear debris).

    Some folks report that Bronze wears better than brass while others write that they have observed bronze bushings are harder on pivots and as a result the bearings experience a higher rate of wear.

    My explanation for the difference in observations assumes that one of the variables not accounted for could be the presence of loose, foreign material in the bearing. This point of view depends heavily on the article written by J.C. Losch previously mentioned.

    In any case, I think we can all agree that a clean bearing will wear at a slower rate than will a dirty one.
     
  24. Time After Time

    Time After Time Registered User
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    Here's what I wrote in another thread which I think kind of addresses some of your observations RC

     
  25. kinsler33

    kinsler33 Registered User

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    So, what happened to your bicycle chain? Did it wear out faster, or did you just clean it and put it back on to the bicycle? My experience with bicycles, which does not include those with aluminum alloy sprockets, is that chains can get truly ugly with layers of dirt and rust, but they do not break. They may become so rusted that they're rendered stiff, in which case the chain must be replaced, but they're usually quite forgiving.

    M Kinsler
     
  26. MuensterMann

    MuensterMann Registered User

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    Well, the chain does not break, but it does cause damage. First of all the chain does stretch, oiled or not. The stretching plus the buildup of grit wears the square topped cog teeth to shark fins. Once you clean the chain after extreme wear, it can no longer work. Both the chain and cogs need to be replaced. The grime also fills in to make it work, but once cleaned - no longer functional.
     
  27. Kevin W.

    Kevin W. Registered User
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    I say use what you think is best, i have put in both, bronze and brass. If i were to rebush a Hermle i would go with bronze as my first choice. I forget who it was, i posted long ago that i put in bronze bushings, he almost tore my head off.Guess its a bit of a touchy subject.
     
  28. MuensterMann

    MuensterMann Registered User

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    Any insight on the purchase of a new Hermle movement with either no bronze bushing on the 2nd wheel versus bronze bushing on the 2nd wheel? Perhaps the answer is - who really knows!! Good maintenance versus no maintenance may be the deciding factor over the years.
     
  29. Time After Time

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    You may want to PM/Conversation Mark Butterworth to ask his opinion. No doubt he has a lot of direct experience to draw upon.

    Outside of that, I agree that routine, preventive maintenance is always going to be the way to go.

    If the owner is someone likely to run a clock until it stops before they take it in for service, a harder bronze bushing may delay the inevitable but will probably result in more pivot wear than a brass bushing would, all else being equal

    ...is what I think.

    Edit: If the solution is to just replace/recycle the movement, bronze would probably be the way to go but ask Mark.
     
  30. R. Croswell

    R. Croswell Registered User

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    Yes I think I remember that. I think that some those who get the most het up about it probably don't understand everything they know. Fortunately we have a choice. Unfortunately most of us won't live long enough to prove if we made the right choice.

    RC
     
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  31. shutterbug

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    Mark used to sell both brass and bronze bushings. He discontinued the bronze, more likely due to low sales than to any other reason.
     
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  32. MARK A. BUTTERWORTH

    MARK A. BUTTERWORTH Registered User
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    The bronze bushings in the second wheels is thicker than simply a pivot hole drilled through the plate giving more contact area with the pivot itself. It is the greater contact area that should give it longer life.
    My view regarding bushings the difference between and and bronze in terms of wear is small if any. The key determinant is the quality of the pivot steel and the polish on the pivot. As an aside, all Hermle movement beginning with a 2019 manufacturing date use stainless steel for the arbors and pivots.
     
  33. R. Croswell

    R. Croswell Registered User

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    Are these shipped with bronze bushings as well?

    RC
     
  34. Kevin W.

    Kevin W. Registered User
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  35. David S

    David S Registered User
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    Mark are you able to tell us what grade of stainless steel they are using?

    David
     
  36. MARK A. BUTTERWORTH

    MARK A. BUTTERWORTH Registered User
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    Hermle makes both the 340-020 and the 1050-020 both with and without the bronze bushngs in the 2nd wheels.
     
  37. MARK A. BUTTERWORTH

    MARK A. BUTTERWORTH Registered User
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    Sorry, but I do know have,that information
     
  38. kinsler33

    kinsler33 Registered User

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    True, and it happens rather quickly on motorcycles, which is an argument for timing belts for these jobs. And when you think about it, it is a rather complex wear mechanism, especially the necessity for wear-inducing grit to maintain the original clearances.

    I mention this because it's quite probable that the wear mechanisms in our old clocks are equally complex and thus difficult to learn and understand. We do not know why some pivots wear and some do not, and why the brass wears and (usually) the steel does not. And it's unlikely that we ever will know unless careful records and measurements are kept, and some good research performed using those records as data.

    It sounds silly, but I think that research on clock ills would have to resemble medical research. Patients and researchers have roughly identical lifespans, as do repairers and clocks (the clocks generally win.) And so what medical researchers do is examine records of both the living and the dead and use that data to learn how diseases are caused and how they run their course. That's why medical records have always been very carefully maintained. Perhaps if we were to establish a data base of clock pathology we could make some scientific progress in our field as well:

    M Kinsler

    But timing belts on motorcycles are ugly.
     
  39. kinsler33

    kinsler33 Registered User

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    Oh: I also like to use bronze bushings when I can because they look cool--rather a contrast to the brass clock plate.
     
  40. R. Croswell

    R. Croswell Registered User

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    Whatever floats your boat if its your own clock. If the clock belongs to someone else I find it hard to justify selecting bushing material for purely aesthetic reasons. I believe the usual objective of quality repair work is to make the repair as inconspicuous as possible.

    RC
     

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