query on smoothing broaches...

Discussion in 'Clock Repair' started by NEW65, Jul 1, 2015.

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  1. NEW65

    NEW65 Registered User

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    Just a query - I'd like all of you who undertakes rebushing to let me know if you use smoothing broaches? I have heard from most clock repairers that they do not use smoothing broaches? So, are smoothing broaches really essential - could this be just wasted money? I would be interested to hear your views on this please? Lets have a vote on here??

    Cheers, Simon.
     
  2. Doug Osborne

    Doug Osborne Registered User
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    When you say rebushing do you mean pressing out an old bushing and replacing by pressing in a new one or do you mean cutting out a worn plate to accept a new pressed in bushing?

    I always use a smoothing broach on the I.D. Of a new bushing.
     
  3. R. Croswell

    R. Croswell Registered User

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    I always use smoothing broaches. It is true that most clocks will run OK if you don't smooth broach but the question is, I believe, a matter of how well and how long the pivot and bushing might last. There are TWO surfaces that make up the "bearing" - the pivot and the pivot hole. Why would one polish/burnish the pivot to a smooth bright finish and run it in a pivot hole that was not equally well prepared?

    That's my 2

    RC
     
  4. shutterbug

    shutterbug Moderator
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    I don't typically use a smoothing broach. I do take extra time to make the hole as clean as possible with the cutting broach by rotating it several times at the finished position. The pivot really contacts only a small part of the bushing, so smoothing the whole thing is wasted effort. I believe (and of course I could be wrong) that a good pivot will do the work of smoothing the bushing surface.
    The manufacturing process used either a drill or a punch to make the original hole. That's it, and many of those lasted over 100 years :)
     
  5. NEW65

    NEW65 Registered User

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    Hi Doug... I mean cutting out a worn hole and pressing in a new bushing. Thank you for your reply :)

    - - - Updated - - -

    Thanks for adding this Shutterbug, your last comment says it all I guess?! :)
     
  6. NEW65

    NEW65 Registered User

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    RC, thanks for your comment, what you mention makes clear sense of why we should use a smoothing broach. Although it does appear to be optional, I suppose you ensure a more professional job if a smoothing broach is used. Each to their own I guess. :) Thanks again for your time and help, I do appreciate it..
     
  7. R. Croswell

    R. Croswell Registered User

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    A number of well know makers (Swiss, German, and others) make smooth broaches. I doubt they would make them if there was no reason to use them.

    RC
     
  8. bangster

    bangster Moderator
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    I always smooth broach pivot holes after pegging. May not HAVE to, but I do. I believe the burnishing work-hardens the inner surface. And it just seems right to burnish the holes after getting them clean.
     
  9. john e

    john e Registered User

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    I also use the smoothing broaches, and believe them to work harden the surfaces a tad.

    As an added bonus, when I accidentally open the assortment pack of 10 different KWM sizes upside down, I use the smoothing broaches to sort the bushing ID's.

    I've only had to do that four times so far...this year..

    John
     
  10. Jerry Kieffer

    Jerry Kieffer Registered User
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    #10 Jerry Kieffer, Jul 1, 2015
    Last edited: Jul 1, 2015
    Simon
    As one who believes repairing a movement by returning it to its original condition, I see no purpose for tapered smoothing broaches. Unless you consider attempting to correct a mess you should not have created with a tapered cutting broach when bushing. The edges of the typical tapered cutting broach are generally very roughly ground and scrape a rough surface in use. Thus a smoothing broach in an attempt to correct the issue??

    In a movement, pivot holes are almost always punched or drilled straight and round since industry including Horological has proven this to be the most effective method. The holes when drilled are cut with sharp drills that cut the metal smooth rather than scrape it rough. They do not use tapered holes or smoothing broaches.
    When rebushing, if straight round holes are smoothly drilled or reamed to proper size and alignment with the arbor, they will function longer with less friction providing the pivot is properly prepared with proper lubrication.

    If a pivot is placed in a tapered hole, it will make no difference if the hole it is smooth or rough since the rotating pivot will only make contact with the high point and burnish its own pocket fairly rapidly. This can easily be observed by inspecting a pivot hole fitted with a tapered broach under magnification after a few months of operation. I had a photo but can`t find it.
    Under these conditions, the hole more rapidly enlarges decreasing proper depthing and more rapid evaporation of lubricants because of less containment.

    While I suppose aggressive use of a smoothing broach could possibly work harden a bushing, there is no industry proof it would have any effect on anything that I have seen.


    Jerry Kieffer
     
  11. john e

    john e Registered User

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    The smoothness of drilled holes is not really that good, nor are punched holes. In production, punching and fast drilling are the most cost effective means.

    The evaporation statement in theory sounds great, however the taper angle using smoothing broaches is so shallow, the surface area increase is not really that large that evaporation would be changed significantly.

    In principle, you are absolutely correct in your feeling that a non tapered hole is better. I would prefer that as well. (Edit: Bergeon has a 30 micron interference fit, KWM is line fit.)The 30 micron interference fit generated by the Bergeon cutter tends to change the ID a bit, so fitting the pivot prior to insertion sometimes closes the ID too much, leaving me to either remove and go one size up hoping it doesn't slip out of the plate, or broach it open a tad. The KWM cutter does actually cause an interference fit, as the brass does tend to flex during cutting, so closes the ID's as well.

    The taper doesn't in principle increase friction. It does increase the force per unit area, and can make erosion occur faster, either wet or dry. Again, non taper is best for that.

    If the tapered hole is rough, that will indeed speed up the wear, as "burnishing" by the pivot can release bits of the brass into suspension, which is not a good thing.

    John
     
  12. David S

    David S Registered User
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    Hi Simon,

    Some how I am not a fan of using a tapered broach to make a nice bushing. I use the KWM system and I try where ever possible to select the bushing that will give me proper pivot to bushing clearance without having to alter the factory ID. I made up a spreadsheet to calculate the so called "5 degree tilt". And it has worked so far.

    I am sure I will come across a situation where the ID of the bush will need some adjustment.

    My problem is that I have no idea if my work with the smoothing broach has achieved the desired outcome.

    David
     
  13. john e

    john e Registered User

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    Do you use different tilts for French?

    John
     
  14. David S

    David S Registered User
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    John I haven't had the pleasure of working on them. I guess I will have to consider that when I get the opportunity.

    While I do have smoothing broaches, and have tried to use them, I have no idea if I am doing anything useful. This is not meant to mean that those with more skill than I have, aren't doing the right thing.

    David
     
  15. R. Croswell

    R. Croswell Registered User

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    AWCI STANDARDS AND PRACTICES
    Available in the permanent threads has this to say about smooth broaching.

    (page 26)General Movement Service (GMS) consists of:


    5.) All pivot holes must be checked for smoothness and to see that they

    maintain the correct
    depthing with the wheels that turn in them. If the

    holes do not conform to these requirements, friction bushings are the

    product recommended for repair. Ideally, bushings should be of the same

    material and hardness as the original plate stock. Where exact

    heights are not available, the bush should be cut down so that the pivot

    clears the bushing hole at both extremes of endshake. (Due to the limited

    availability of bushings of differing brass composition and hardness, brass

    bushings should be used in brass plates and bronze bushings when

    replacing bronze bushings.) When pivot material is of poor quality (i.e.,

    plated or soft steel), bronze bushings may be the best choice for repairs. All

    holes should be burnished to brightness with a smoothing broach
    (emphasis added)
    .
    The hole

    that is reamed to receive the bushing should be chamfered on both sides of

    the plate to reduce the presence of flashing which can throw the bushing off

    center or tilt it. The bushing should be pressed or tapped into place,

    maintaining the plate's appearance, without damaging either the bush or the

    surrounding plate finish. Once the pivot hole is reamed to size, the hole

    should be burnished with an oiled smooth broach (like the other holes) and a

    proper oil sink cut to match other oil sinks on the plate.
    ..................

    Not taking sides.

    RC
     
  16. Jerry Kieffer

    Jerry Kieffer Registered User
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    #16 Jerry Kieffer, Jul 1, 2015
    Last edited: Jul 1, 2015
    John
    While I will agree that punched and drilled holes are not necessarily that smooth, they are generally better than taper broached holes if for no other reason than they are non tapered.

    Taper broached and smoothed holes have a number of issues. The most important being that it is a "Get Lucky" approach with no way to assure sizing other than developed skill. Unfortunately, those I have observed over the years are in most cases far to large especially on the large side of the hole.

    Your statement that a taper hole will not increase friction is not correct or supported by proven industry methods.

    If a bushing hole is properly aligned parallel with a Arbor, fitting of that pivot can be much tighter than if not. In fact, it can be fitted tight enough so that the pivots in the upper end of the movements will ride on a oil film greatly decreasing friction.
    This is something that can be demonstrated. Some years ago, when the St Louis Regional was held at the Breckenridge Concourse Hotel, I did a public demonstration on this during a Seminar presentation. I can explain how if anyone is interested.

    Predetermined hole sizing and alignment is actually very simple per attached photo.

    You can simply ream the desired size hole using the opposite pivot hole as a guide for proper alignment.

    Traditional Horological repair suggestions (Both watch and Clock) are in many cases in direct conflict with manufacturing methods. Personally I put more faith in Manufacturing methods since they actually manufacture movements that prove their methods to be superior.

    Jerry Kieffer
     

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  17. shutterbug

    shutterbug Moderator
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    #17 shutterbug, Jul 1, 2015
    Last edited: Jul 1, 2015
    Love it, RC - and you have my respect for your knowledge and involvement here on the MB. I do notice though, that the standards and practices 'rules' do not have research related information regarding how the standards were arrived at. Jerry almost always has a reasoned experienced based explanation for his opinions. You do as well. However, the AWCI standards and practices do not provide that kind of reasoning and because of that, have to be accepted on word only. I'm not comfortable with that approach. I'm not saying they are wrong. :) I do use tapered broaches, but prefer the inside/outside broaching technique. That method will leave the inside of the hole smaller than either of the outer extremes. Not perfect, but good enough for the types of repairs that I do. The wear will then be at the inside of the hole first, and over time will expand to both outer areas equally. Will it create a groove in the pivot? I don't know the answer to that.
     
  18. Hudson

    Hudson Registered User
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    Interesting question about smoothing broaches. I am also trying to find methods that work for me when bushing clock plates. A typical smoothing broach that I just measured has about 0.008" inch/inch of taper. Now a machinist working on industrial machines, would have to say that is a LOT of taper. It would, for example, be unacceptable for a motor, pump, or turbine bearing journal to have that much taper.

    A clock plate is kinda thin. Some American clock plates are around 1/16th inch thick. For that distance, the taper through the plate would be about 0.0005"

    So I think about it and read and watch and listen. I have found that many clock repairmen actually work more by "feel" than by measuring to make parts fit to a certain tolerance level. Some broach the bushing, with a tapered cutting broach, until the pivot just starts into it or maybe just goes in kinda tight, then they open it up the final bit with the smoothing broach. I have had them emphasize that the broach should be used from both the inside and outside of the plate. If that were done perfectly even on a thin plate, then there would exist a .00025" taper from each side to the middle of the bushing. It takes a keen feel to do that. And different repairmen have different opinions about what feels right.

    Regarding the 5 degrees of "tilt", I had a hard time getting my mind around that one. I made a spreadsheet that calculates the radial clearance based on the plate thickness, the pivot diameter, and the angle of tilt. 5 degrees of tilt can produce a lot of clearance or not so much depending on the thickness of the plates. I'd rather measure the pivot and measure the pivot hole, and know what the clearance is.

    I would like to put a clock together like a piece of precision machinery, but being able to do that with the tools available (at reasonable cost) has been elusive to me.

    Clock repair people get by with lots of different methods. They take a clock that doesn't run, clean the movement, close up the excess clearances to something that works, and lubricate it. Then it runs for a time that exceeds their one year or so warranty.

    I'm going to bush my clock plates using my milling machine. I did my first one with the mill last week and the results are quite good. I tested the method with a really worn out cuckoo clock movement that needed every pivot hole bushed.
     
  19. bangster

    bangster Moderator
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    Jerry what is the tool with the handle in your picture?
    (And what is the black iron thingy in the movement?)
     
  20. Jay Fortner

    Jay Fortner Registered User

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    Smooth broaching does three things. It smooths the bore,works hardens it's surface and seems to break debris free that pegging misses. I discovered that while smooth broaching I was removing black residue that didn't come out during pegging. It could be debris that is embedded in the surface of the hole. I peg while prewashing in mineral spirits then the parts go into the US and thoroughly rinsed then I peg again until the pegs come out clean. Then smooth broach and when I peg after broaching there is always a little black "stuff" on my peg. If you wipe the oil off your smooth broach with a white paper towel you will see the black dirt that gets left behind. It is a time consuming PITA to do all that pegging,smooth broaching and pegging again but I feel it is a necessity to do a thorough job.
     
  21. leeinv66

    leeinv66 Moderator
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    Smoothing broaches do one thing here and that is sit in the bottom of a draw. :whistle: I prefer to work on weight driven Vienna movements and spent many hours experimenting and trading notes with our departed friend Scottie-TX on running these movements on minimum weight. What I can tell you is all the movements I experimented with required more weight to run when initially repaired and put on test than they did after they had been running for several days. Burnished pivots nor smooth broached bushings made any difference in my observations. My conclusion is the same as Shutterbug's, the only work hardening needed is that which happens naturally as each pivot mates with its bushing.
     
  22. R. Croswell

    R. Croswell Registered User

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    Jay, I keep hearing that smooth broaching "work hardens" the bushing, and folks keep repeating that but as Shutterbug asked, is the documentation? Perhaps it does but I have my doubts, plus the bushings we all use should already be sufficiently hard.

    Like you, I always peg after smooth broaching and always get a little "dark stuff", even with a brand new bushing so I do not believe it is dirt or debris. More likely me thinks is very fine metal particles removed from the bushing and the oil used on the broach. The smoothing broach is not smooth but sort of like a super fine file.

    This is an interesting discussion but I believe we are considering three different situations and looking for a single answer - that is manufacturing methods, repair methods, and remanufacturing methods. Perhaps the question might have been do you use a tapered smooth broach following the use of a tapered cutting broach? We might also pose the question, does smooth broaching do any harm?

    There are a lot of theoreticals here and I believe that perfectly aligned bushings with perfectly parallel sides and smooth surfaces fit to a close running fit in thick plates and a ridged movement would be ideal. In the real world, especially with typical American clocks and thin plates, the dimensional difference from one end of the bushing ID to the other from a tapered cutting/smoothing broach is only a tiny amount. Broaching from the outside of the plate to a little less than "running fit" and taking a final cut from the inside leaves a very slight raised center in the bushing. Running the smoothing broach won't remove the raised center but will help smooth out any ridges and grooves from the broach. Having a raised center will actually allow the plates to squirm a little under the tension of the springs/weights. I do believe that there will be a break-in process where the pivot mates with the bushing surface as some have suggested. I hope that the use of the smoothing broach would provide a better starting surface such that less metal would be removed during the break-in period but that's a gut feeling and not something I can personally document.

    In the clock repair environment bushings will continue to be installed by hand and with the help of various fixtures "machines" and bushings will continue to be opened using tapered cutting broaches. So unless someone can substantiate that smooth broaching such bushings has some negative effect i'll keep doing it. Of course I'm not working against the clock to get something out the door.


    That's my nickel's worth.

    RC
     
  23. Jerry Kieffer

    Jerry Kieffer Registered User
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    #23 Jerry Kieffer, Jul 1, 2015
    Last edited: Jul 2, 2015
    Bangster
    The reamer is a Gage pin sharpened to about 12 degrees on one end that will enlarge an existing hole in the same manner as a reamer. Gage pins are hardened and ground to size and when sharpened in this manner, have a razor sharp cutting edge that produces a straight round hole with a very smooth finish to exact size.
    Since Gage pins come in sets that are in .001" increments, a pivot can be measured and the correct size selected for an assured preferred pivot hole size. This saves time over hit miss broaching and returns the movement to original condition. Because a Gage pin is the same size over its length unlike broaches, you can enter the opposite pivot hole and use it as a guide for assured arbor/pivot hole alignment in a new bushing or repair.

    The Black thing you mentioned, is a piece of .500" hex steel machined to except a WW collet with a closing nut and utilized as a Pin Vise. With a set of collets, this eliminates all of the holding and sizing issues with pin vises.
    In this case it is being used to hold the Gage Pin for the reaming example. Because it was accurately machined, it can also be quickly mounted in a lathe or Mill to machine what is being held if beneficial.
    A more detailed Photo attached.

    Unless of course you are referring to the bent part in the middle of the junk movement used for demo purposes.

    Jerry Kieffer
     

    Attached Files:

  24. bangster

    bangster Moderator
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    Hooray for you, RC. I think you've got it right.

    Some peripheral comments:
    *Cutting broaches are used for two things: to enlarge a hole in a plate, in order to insert a bushing, and to enlarge the ID of the bushing. I can think of no other reason to enlarge a pivot hole in a plate, except to introduce a bushing. In that use, it's indispensable to those who do hand-bushing. Perfectionists, like Jerry, seem to believe that hand-bushing ought never to be done. But without it, countless clocks would be consigned to the garbage. ("Better dead than hand-bushed."

    *Bushings should seldom need to be enlarged with a cutting broach. Select a size that best fits the pivot, and if it's a little loose, better than too tight. A too-tight bush can be opened incrementally with a smooth broach, until it's right.

    *A smooth broach is like any burnishing tool: it will remove a miniscule amount of metal, but its main purpose is to upset the surface irregularities, mash them down instead of removing them, and in the process deforming the surface of the metal. Deforming cold metal, without removing it, is almost a definition of work-hardening. Burnishing work-hardens the metal a few molecules in. Work-hardening a bronze-age sword by beating it on an anvil made it almost as hard as steel. Metallurgists can explain the details, but those are the basic facts: deforming cold metal makes it harder. Bend a piece of wire back and forth until it breaks; it doesn't break because it got softer at the bend, but because it became hard and brittle.

    *To the extent that a smooth broach deforms the inner skin of a pivot hole or a bush, induces work-hardening in the skin. Whether that work hardening of pivot holes improves the behavior of a clock has probably not been pursued in scientific horological circles as much as it should. But that it happens should not be in doubt.
     
  25. bangster

    bangster Moderator
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    I like that. Tell us more about turning Gage pins into precision reamers. And using them.
     
  26. leeinv66

    leeinv66 Moderator
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    Call me Thomas as I still doubt it.
     
  27. Jay Fortner

    Jay Fortner Registered User

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    Sorry man,I'm not buying it.
    Once I started smooth broaching I notice a definite reduction in friction. Spring wound clocks that would run 10 days on a wind went to 14 and I was able to run lighter springs. I haven't bought an .018" mainspring for an American T&S in four years. Weight driven clocks started chiming and striking faster.

    Now why would a pivot work harden a hole and a smooth broach won't?
     
  28. Jay Fortner

    Jay Fortner Registered User

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    Hmmm,I have wondered about that as well. I would think metal debris from new bushings would come out looking like brass,not black dirt.

    The only reason I say holes are work hardened is because it has been documented so many times by so many different authorities with certifications up one sleeve and down the other. We know brass hardens as it is worked and quite quickly. You can bend a piece of sheet brass once but try to bend it back and it cracks or snaps off.

    You nailed the olive hole scenario perfectly. I have tried to run thin plate/small pillar/spring wound clocks with close tolerance straight holes and they won't run when the springs are wound up,they need to be able to shift and not bind the pivots.
     
  29. R. Croswell

    R. Croswell Registered User

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    I believe that if the metal particles are fine enough they will look black. Take for example the silver that makes up a black and white photograph looks black, not like what one thinks of as silver.

    I'm still not convinced that smooth broaching work hardens the bushing. True that hammering and bending and that sort of working does, but cutting, cutting, and filing? Never heard that documented but perhaps it does. But what's the point? Aren't the bushings already as hard as they should be? I've heard stated here (not that I agree) that hard bronze bushings "eat" pivots. So what's to be gained if broaching did work harden pivot holes?

    RC
     
  30. leeinv66

    leeinv66 Moderator
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    Shoot Jay, I notice similar improvements every time I rebuild a movement. If I didn't gain a reduction in friction from a rebuilt or serviced movement, then there really wouldn't be any point in doing those tasks in the first place. You either buy this work hardening business or you don't. You do and choose to use smoothing broaches. I don't and choose not to use smoothing broaches. I am confident in the choice I made based on my observations.
     
  31. Jerry Kieffer

    Jerry Kieffer Registered User
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  32. shutterbug

    shutterbug Moderator
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    I'm with Peter on this. When Jay asks: "Now why would a pivot work harden a hole and a smooth broach won't?" I have to wonder: 'but if both will do the same task, why is one better than the other?' That seems to be what it comes down to.
     
  33. R. Croswell

    R. Croswell Registered User

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    My take on it is that if some of the initial "peaks and valleys" are knocked down with the smooth broach then there will be a bit less enlarging of the pivot hold by the pivot during the first weeks/months of operation. I may be wrong, but I'm not buying the hardening part - just the smoothing part as the name implies. Not saying it has to be done to be a reliable repair.

    RC
     
  34. Jay Fortner

    Jay Fortner Registered User

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    They do. Here recently I've been doing service work on movements that were overhauled by one certain shop that installed bronze bushings. I know this because they leave their stickers on everything it the clock with the job number on it. Twenty years later the pivots that were running in bronze bushings have been chewed up more than the pivots that were still running in the plates with 100+ years on them.
     
  35. shutterbug

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    But bronze has a bit better coefficient qualities than brass. I'm curious about why they would chew up a steel pivot?
     
  36. Randy Beckett

    Randy Beckett Registered User
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    I think it is the pivots condition that determines how well and long the bush lasts. Whether work hardened on the surface or not, it would make little difference whether a bush lasted a hundred years. It could only last that long only if the pivot remained perfectly smooth for a hundred years, as it still comes down to a piece of steel rubbing against brass.


    It seems if the pivot hole is in the right location, is square to the pivot, fits the pivot closely, and is clean, that the pivot will still mate itself to the pivot hole in a few days or weeks of running. This mating process is because of a ever so slight amount of wear to the brass, and will happen no matter how the pivot hole was finished.


    The one thing that higher quality clocks, with reputation of not wearing, have in common is smallish, very smooth, and very hard pivots. I think it likely that this hardness is the key to the long service, as it keeps the pivot smooth as turns for those hundred years.

    I think I am in Shutterbug and Peters corner on this one.
     
  37. john e

    john e Registered User

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    We are in agreement. The salient statement you made is "not necessarily that smooth. I concur that in principle, non taper is better, with the caveat I will mention below.

    That statement is entirely incorrect, however there are distinctions. The coefficient of friction is independent of the taper hole and angle. It is independent of the fit of the pivot to hole. It is dependent on the materials and the normal force.

    In "industry", other issues come into play. As a lubricated surface, the float between two elements can be compromised by the force per unit area and the viscosity of the lubrication. A tapered hole and cylindrical pin will by definition, increase the force per unit area, so the lubrication can be more easily compromised by normal force. Again, non tapered is the ideal, assuming alignment is perfect (it isn't despite your (our) best efforts, I'll discuss that below.)

    I am interested.

    An excellent methodology. Issues discussed below.

    That aspect is in my opinion, VERY important. I try to teach that fact to students, especially the degreed engineers, they need the hands on experience and understandings.

    By machinist standards, that is indeed a lot. However, assembly tolerances sometimes make it necessary, especially a reworked unit.

    I know it work hardens the surfaces, as any movement even at the grain level will do that. But as to doc's, I'd also google it.. I have experience with stainless surfaces becoming magnetic as a result of surface scratches at the 10 micron level, and have seen photomicrographs of surfaces smooth broached. IIRC, Penman gave an incorrect assertion of work hardening not happening due to lack of gross movement, and I wonder if that was his origional thought or a carry-down from another.

    Excellent, I really like it. What happens if the bushing you replaced also needed the pivot dressed down (no, not yelled at) due to damage? You end up with a smaller pivot on the reqorked bushing end, and now the gage pins do not work. In fact, if you have to dress down the pivot 300 microns radially, you have now a taper consistent with my Bergeon smoothing broaches.


    Here here...please do.

    Smoothing will bring the movement closer to the long term condition, there will be less change. Somewhat akin to the old "break-in" of cylinders.

    Personally, I'd rather have the bushings go instead of the pivots. Replacing worn bushings is a lot easier than replacing a worn pivot.


    Ok, a little math..

    My bergeon smoothing broaches, measured 60 mm apart along their length, have a diameter difference of 600 microns. This is a taper of 300 microns per 60 mm, or an angle of .3/60. That is 5 milliradians (mRad). (I use milliradians for a very good reason, at angles close to zero, one can assume linearity between offset angle and offset/length. A 1 inch long arbor tipped 5 mRad will have a 5 mil (.005 inches) horizontal offset at the far end. A 60 mm long arbor will have a 300 micron offset if it tilts 5 mRad. (.005 times 60).

    The gage pin technique is absolutely fantastic, but it neglects what the final assembly configuration is. If I take a mantle movement and work it using gage pins, then it will have PERFECT alignments when the movement is assembled, but NOT when the springs are wound. An examination of the force distribution (Maxwell Cremona diagrams to tweak those who remember them) will show that the front and back plates are being sheared by the assymetrical force caused by the spring centered on the posts, but delivering working power very close to one of the plates. This WILL cause the plates to rotate relative to each other in two degrees of motion. With this, pivots which were perfect and very close tolerance will now bind. I am confident most have found this to occur. If the holes in one plate have shifted 300 microns, you are now at the angle where my Bergeon broaches have produced the PERFECT taper angle, while gage reamed are now OFF by 5 mRad but hopefully do not bind..

    I also find that when a movement is screwed onto it's mounting plate, care must be given to how the mounting screws BEND the plate. Take great care to remove the tendency of the overall assembly to do that. The movement cannot rock prior to tightening the screws.

    When installing a movement in a grandfather, it is very important that the wood platform does not try to bend the movement during tightening of the clamping screws. The twist of the top surface of the platform is partially important, as well as where the plates touch the surface (grooves).

    If the platform is flat but the mounts on both sides are not coplanar, the weights can also force the platform to twist. If that twist is transferred to the plates, too tight bushing/pivots will give problems as well.

    Hence the 5 degree recommendation. That is an engineering (well, ok, experience based as well) criteria which does serve well. Most of us are not setup to measure plate to plate shear at the 300 micron level, nor at any level for the most part. If one wants to go tighter, then it is important to work the movement under the worst conditions to guarantee that the tolerances do not bite you. Go really tight, you set yourself up for multiple dis-assemblies. Me, for personal work, no problem. For a customer, they will not pay for the excess.

    John
     
  38. Jerry Kieffer

    Jerry Kieffer Registered User
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    #38 Jerry Kieffer, Jul 2, 2015
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    John
    The Gage pin reamers do not ream tapered holes. They line bore a hole straight and round based on alignment positioning with the sole purpose of recreating an original manufactured condition. Hole sizing is then based on the original hole to pivot sizing ratio where one relies on the manufacturer to size pivot holes based on the movement characteristics and design criteria. Per something like your Main spring example if I understand it correctly.

    Personally, I have not come across an example of a movement with rotating plates under spring tension or a manufacturer with this as an issue. Not sure how you would get a twisting effect on two plates when each has the exact same forces applied to them in the same directions.

    At any rate, if you have a pivot that needs 300 Micron removed to dress it properly, it is probably a good candidate for replacement in many cases. However if not, even the tightest fitted pivot allowing friction free operation would easily
    compensate for a 150 micron miss alignment over the width of a movement.

    Jerry Kieffer

     
  39. john e

    john e Registered User

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    The softer material will embed particulates, and the particulates will attack the harder part.

    John
     
  40. john e

    john e Registered User

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    #40 john e, Jul 2, 2015
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    I understand they do not ream tapered holes. My point was, yes they produce an aligned set of holes which form a perfect cylinder, but if one pivot is slightly smaller in diameter, you lose the ability to use your gage pin reamers. Then, you have to rely on using a smaller reamer and centering the root in the opposite hole as best as possible.


    Yes, you have. If you have worked on a spring clock, you have worked on an example.

    Examine a typical mantle clock. The springs will pull on the center of the posts, as you mention. However, look at where the wheel transfers it's power to S2 and T2. That is always at one plate. So the reaction forces to compensate the center of post forces are not symmetrical to the plates.

    As an example, a spring pulls on the center of a post at 1Kg. Each plate must "push back" 500 grams. The plate with the wheel next to it will receive all the 1Kg force. The plate on the other side still needs 500 grams, where is it getting it? From the posts, all 4 or 5 of them. You cannot expect those posts and the brass plates to be infinitely strong, they will flex. If they flex 100 microns in plate to plate shear near the fly's, then the fly's will have that misalignment, with all arbors misaligned proportionally to the ratio of distance to the spring post with respect to the fly's. (half the distance, half the misalignment). Edit: in reality, the proportion delivered to each plate by the spring will be modulated by the stiffness of the post to plate mechanics. It is indeed possible to make a plate and post so thick that the backside plate is not even needed, but we all know that doesn't happen. Typically, the plates are designed historically to some thickness, unless the manu is really cheap and goes thin, making our work even harder.

    The concept that it is important to have perfect cylinders and perfect pivots in perfect alignment is great and ideal. However, in the perfect world, forces will conspire to prevent that. Using your technique, even a 50 micron or 100 micron drift destroys the concept of a line contact along the pivot to bushing.

    I'm working a time and strike tonight, 4 bushings to do (using the bushing tool I made last weekend). If I get a chance, I'll slap together a dial indicator on a slab of 1/4 inch aluminum with a hardstop so that I can zero the indicator with springs let down, then wind one then the other and watch the indicator. I am totally curious as to the level of effect on the piece I'm working on as an academic exercise.

    You've missed the point. Your technique provides absolute true line contact on a non wound movement. In situ forces on the movement in use will destroy that perfection, leaving you with point contact. The real question then becomes, what level of fit is required to remove those deflections from the picture.

    If you had a tapered sleeve for each gage pin to center the root, then that would work perfect as well. Leaving you only to consider flexing of the movement in real use.

    John
     
  41. Jerry Kieffer

    Jerry Kieffer Registered User
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    #41 Jerry Kieffer, Jul 2, 2015
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    John
    You have missed my point completely. I am offering options for returning a movement to its original specifications in timely fashion as it came from the factory. Most have ran for many many years without issue having proved themselves and the reasons for returning them to their original condition.

    The Question is, will yours and others modified versions provide the same level of service :???:?

    Jerry Kieffer
     
  42. harold bain

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    Interesting discussion.
    Over the years I have become less critical of the amount of movement of pivots in their bushings in American movements, if there are no ovalled holes. I know many repairmen replace every bushing when overhauling a movement. I focus more on obviously worn bushings with the ovalled holes that you know are a problem. With perfectly round holes, if there is any wear it has to be the pivots, unless they were made that way. And usually there is no obvious wear on the pivots on these, not requiring the removal of any significant amount of metal in smoothing and burnishing the pivots. Higher in the train, close to and including the escapewheel, I am less tolerant of wear.
     
  43. bangster

    bangster Moderator
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    #43 bangster, Jul 2, 2015
    Last edited by a moderator: Dec 31, 2017
     
  44. Jerry Kieffer

    Jerry Kieffer Registered User
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    #44 Jerry Kieffer, Jul 2, 2015
    Last edited: Jul 2, 2015
     
  45. leeinv66

    leeinv66 Moderator
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    I have to agree with everything Harold has written here. Sometimes bushings are done because the repair can, rather than needs to.
     
  46. R. Croswell

    R. Croswell Registered User

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    That's the difference between "remanufacturing" a clock putting everything back to factory original specifications, and "repairing" a clock to make it run well for a reasonable length of time. Here reasonable is at least as long as until the next time it needs to come apart for regular service when additional bushings can be installed if needed. Then there is the whole discussion that was here a few weeks ago on preemptive bushing.

    There are other reasons to bush than a worn pivot hole. I have one on the bench now where several pivots were badly worn and irregular so I had to turn them which made it necessary to install an undersize bushing. There was also one previously installed bushing that was tilted and off location by half the pivot diameter. So cleaning up other's mess is another reason to bush. Note this clock came in with the complaint that it "sometimes unwinds itself" so I guess I didn't need to do any pivot work to make it run but it would surely be back with the complaint that "you fixed it last year and now its not running again already". So yes, I probably do a little preemptive bushing work but I don't go overboard.

    RC
     
  47. leeinv66

    leeinv66 Moderator
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    RC, there is an inconstancy with your re-manufacturing analogy. You go on to say you might re-bush because you have damaged pivots that need to be turned down to make them usable. Well, if you were re-manufacturing would not replacing the pivots with ones of original specs be the correct action? Just saying;)
     
  48. R. Croswell

    R. Croswell Registered User

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    If I were remanufacturing a clock I would agree, but that is not what I do although I often do more than the minimum.

    RC
     
  49. bangster

    bangster Moderator
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  50. leeinv66

    leeinv66 Moderator
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    Several of my clocks have been running almost continuously for more than 25 years. While they required extensive repairs to get them back into working order, I have not had to repair any of them since. Every five or so I pull their movements and inspect them. To date, none have required more than normal cleaning and re-oiling to see them back in service. Doing the minimum is working out ok for me!
     

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