removing broken plate screws

Discussion in 'Watch Repair' started by tracker, Nov 6, 2019.

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  1. tracker

    tracker Registered User

    Aug 15, 2007
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    Does anyone know of a way to remove broken plate screws from a 18 size full plate pocket watch? The heads of the screws are completely missing and only the shaft of the screw can be seen. I would like to remove the screw without damage to the treads of possible. Thanks.
     
  2. gmorse

    gmorse Registered User
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    Hi tracker,

    Have a search on this MB for 'Alum'.

    Regards,

    Graham
     
  3. musicguy

    musicguy Moderator
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    Moving thread to watch repair where it will get better attention.



    Rob
     
  4. karlmansson

    karlmansson Registered User

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    A screw with its head missing usually doesn’t have any tension keeping it in place. Can you remove the other screws and simply lift the plate free off the remaining screw? If not, you should be able to tease it out with an oiler or similar. For screws that have partially broken heads I refer to previously given advice.

    Regards
    Karl
     
  5. Al J

    Al J Registered User

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    You know, as much as this advice makes perfect sense and I see it given often, when I get a screw with the head broken off, it is rarely loose...

    I'm actually surprised when I can tease out a screw that has the head broken off, as most of the time it's still jammed in the threads. Maybe I just have bad luck in this regard, but I would love to hear if other people find that screws with heads broken of are usually free and easily removed...

    Cheers, Al
     
  6. Skutt50

    Skutt50 Registered User

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    For some reason the screws I manage to back out are often left hand threaded typically crown wheel screws.
    I also have had some sucess with ratchet wheel screws. Culd it be because these screws have thin heads which break without too much force?
     
  7. Jerry Kieffer

    Jerry Kieffer Registered User
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    Al
    Other than the ones mentioned by Skutt, most others that I encounter are not loose enough to be removed with a pick.

    I mainly work on what others have not been able to easily remove and they do not want any visible evidence of removal or the part having been worked on. As such, I personally avoid the use of chemicals in favor of two other methods of removal.

    (1) For larger pocket watch size screws, I use a SKS 300,000 rpm mini die grinder with a micro carbide bur to cut a screw driver slot. Size comparison of the grinder and bur can be seen in the first two photos.

    (2) For smaller screws, I drill them out in a Small Milling machine configured per the third/fourth photo. In this case, the Mill configuration allows for very clear optical observation of the drilling procedure. In addition, this allows the use of the "X" axis for drilling that is far more comfortable and natural than the "Z" axis in the vertical configuration. In addition, it offers greater tool feedback.


    (3) The critical part of drilling is to establish a "centered" center spot. In order to assure this, I first machine a flat spot on the threaded screw section with a center cutting stub endmill and then spot drill in the center for drilling. This allows the spotting drill to do its job without any rough jagged off center stresses. The screw can then be drilled and removed with an easy out or by drilling up to thread size and easily chipping out the remaining thread pieces. All tools are carbide specifically designed for hard steel. Fifth photo, shows stub endmill top, spotting drill center and drill third for appearance and size reference for anyone interested. None of these are available in Horological supply out lets, but readily available through reputable machine tool supply houses. They and other far more complicated/capable micro tools can also be viewed and sometimes demonstrated at international machine tool shows.

    Hands on experience again for anyone interested, can be had at selected NAWCC workshops by contacting the educational director for further information.

    Jerry Kieffer

    fullsizeoutput_470.jpeg fullsizeoutput_475.jpeg fullsizeoutput_477.jpeg fullsizeoutput_47a.jpeg fullsizeoutput_472.jpeg
     
  8. viclip

    viclip Registered User
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    This may or may not be relevant to watch screws ~ however as a former motorhead who's done his reading respecting SAE fasteners, the respective male & female threads are friction fit when an automotive bolt is torqued down.

    So even with the head snapped off, these fasteners won't necessarily nicely turn out.

    I suppose it makes sense that the same considerations could apply to watch screws.
     
  9. Rick Hufnagel

    Rick Hufnagel Just Rick!
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    I've been reading about you guys using alum.

    I'm not excited about it, but I have a chance to experiment with it.

    The balance cock of my new Hampden has a stud screw buried in it, with no head. Tiny... Tiny.. thing.

    I feel it's relevant to this thread to ask those with experience, does the alum discolor Gilt?
     
  10. DeweyC

    DeweyC Registered User
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    Rick,

    I do not know about how alum reacts to gilt plates. Do you have an old plate to try? Be sure to remove all the other steel.

    Also, another technique to try is to put the plate in the ultrasonic. Surprising how many times it works. If it is friction tight, try a soldering iron on the plate near the screw (now a stud) but not touching the steel. The object is to expand the brass/nickel enough to reduce the friction.
     
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  11. Rick Hufnagel

    Rick Hufnagel Just Rick!
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    I will report back after the weekend with the results, thank you sir! Definitely will try a junk plate first.

     
  12. gmorse

    gmorse Registered User
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    Hi Rick,

    I know this works fine on fire (mercury) gilt plates and I haven't found it to discolour them. However, I'm not so sure about electroplated surfaces, where the gold coating is typically thinner than that on fire gilt objects and the adhesion of the gold layer may not be as secure. If you're at all unsure of the nature of the gilding, better to go with one of Jerry's mechanical methods of removal.

    Regards,

    Graham
     
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  13. viclip

    viclip Registered User
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    I've seen others suggest that steel parts not to be dissolved in alum, can be coated with grease & thereby conserved while just the broken screw is attacked. I've never had occasion to try this however if this methodology does work to protect steel, then I would think that it could be used to protect gilded plates, cocks etc.
     
  14. roughbarked

    roughbarked Registered User

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    I keep a hand graver, sharpened for this, as mentioned above the screw can be teased but if tight the graver works better than the oiler because it can dig into the screw and be used to tease the screw out.
     
  15. karlmansson

    karlmansson Registered User

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    I usually make a fine scratch with sharp graver across the remaining end of the threaded rod if its protruding so that a small screwdriver can grip it. That, or dig the tip of the graver into it and rotate.

    I mean, it *should* be loose considering the mechanics at play. Then again, breaking a steel screw off takes some force considering how fine the threads are. Maybe the threads have distorted and compressed into the screw threads prior to the screw breaking?

    Regards
    Karl
     
  16. Skutt50

    Skutt50 Registered User

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    It does work! I do it quite often but I use bees wax to protect any remaining steel. I have however never tried to coat an entire plate.
     
  17. gmorse

    gmorse Registered User
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    Hi Karl,

    I think this is probably what's happening. A fair proportion of broken screws are in the keyless work, likely to have left-hand threads and hence prone to over-tightening in attempts to remove them the wrong way.

    Regards,

    Graham
     
  18. Al J

    Al J Registered User

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    I've been thinking about this since I wrote my post above, and I think you and viclip are on the right track:

    Thinking back to my days in school for engineering and my mechanics of materials courses, I think these observations help explain why a lot of broken screws I see aren't loose. A screw thread is an inclined plane wrapped around an axis. When tightened, the head does provide the tension on the threads, and this load leads to elastic deformation of the thread. If the head snaps off at this sort of load, then the tension is released and the screw is loose in the tapped hole.

    So soft screws (like you see on Seikos often) or screws where the head is thin or the slot is cut deeply in relation to the head thickness, and the screw seems to twist off with not much force, these are likely to be removed easily all else being equal.

    For a screw that requires a higher torque to break the head off, by the time the head actually snaps off the thread may move from elastic deformation to plastic deformation. This would mean that releasing the tension when head breaks off doesn't leave the screw loose in the tapped hole. The remainder of the screw will be jammed in the threads due to this deformation.

    So it's likely related a great deal to the forces required to break the head of the screw off, if the remainder of the screw will be easy or difficult to remove. I'm guessing that there are lots of other factors involved, such as the class of fit of the screw, if the tapped hole is somehow damaged or contaminated, etc.

    Anyway, interesting discussion.

    Cheers, Al

     
  19. viclip

    viclip Registered User
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    In the automotive sphere at least, fastener "stretch" is closely allied with proper torquing procedures. As the fastener is tightened it is also stretched (we're talking very small amounts here) resulting in an enhanced locking effect at play between the male & female threads. This is taken into account in the torque specs (which explains why equivalent grade replacement fasteners should always be used when working on your car!).

    The best example of such "stretch" arises in the context of tightening down the caps which affix the piston connecting rods to the crankshaft. The best practice is to avoid relying on a torque wrench when tightening down these critical fasteners. The nut for the con rod bolt is tightened down until the bolt stretches the specified amount, as measured by a micrometer or perhaps these days by a digital Vernier caliper.

    Admittedly con rod bolts are special fasteners but still this serves to further illustrate the internal thread locking dynamics.

    And since watch screw heads are normally broken off courtesy of over-tightening esp. the lefties, I would expect the poor little screw stem to have been stretched in addition to being subject to any pre-existing friction fit between the threads.

    Just a few thoughts.
     
  20. Jerry Kieffer

    Jerry Kieffer Registered User
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    There are a number of issues with short thread large headed screws especially left hand holding various wheels and other items.

    (1) With large headed screws, one has a tendency to use a screw driver much larger than intended for the size of the thread. Thus the tendency to over load and snap the small threads without realizing what is happening if not experienced.

    (2) Of course with a larger screw driver, and not knowing if a screw is left hand thread, is an accident waiting to happen.

    (3) However, I suspect the major cause of breakage is that the screws used in areas where length is limited, will often be undercut to assure unobstructed seating against an arbor. For whatever reason, they are often undercut below the base of the thread creating the weakest area of the screw just under the head. The attached screw photo from a Elgin movement shows such an example.

    (4) As far as locked threads, Hardened threads as common in Horology will not lock up or deform as with soft threads. (Or at least I have never seen it) Again however, unless screw threads are perfectly clean and dry when installed, fluid contamination will dry and cement threads together over time. The screw in the attached photo just happen to have such an issue and snapped loose under heavy tension. Under close inspection of the photo, the contamination can be seen. The movement it came from appeared very clean, but is a junk movement with no known history.

    Jerry Kieffer

    fullsizeoutput_47b.jpeg
     
  21. Al J

    Al J Registered User

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    The screw is only half the equation...
     
  22. Jerry Kieffer

    Jerry Kieffer Registered User
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    Al
    It should have read where both male and female threads are hard, they will not deform and lock up like soft threads can under the right conditions. However, in the case of the 1.2mm x .25 pitch screw (very close) in the photo contains 5-6 threads. The surface contact area of those 5-6 threads is roughly 1.5 times that of the undercut area below the screw head. In this case, the screw head will snap or twist off long before any thread issue hard or soft. Of course assuming my quick math is correct.

    Jerry kieffer
     
  23. Tim Fitzgerald

    Tim Fitzgerald Registered User
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    I have used most of the methods that have been mentioned and each one has worked under different circumstances, the alum worked for one that was broken off too far down the hole , using a screw head file worked when I had a little bit of head protruding, drilling a tiny hole & using a screw extractor has worked once. All need to be used with caution . I tend to be ham -fisted & impatient which is hard for me to control. Alum worked more times than the others, also required the most patients.
    Good luck Rick
     
  24. Marty101

    Marty101 Registered User
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    Heat that alum up. The heat increases solubility and you can save 75% of your time. I use a coffee cup warmer to heat my solution,and those dead head screws turn black in no time.
     
  25. Tim Fitzgerald

    Tim Fitzgerald Registered User
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    I'll have to try that , Thanks Marty
     

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