Mechanical WW Patience is a virtue....unless

Discussion in 'Watch Repair' started by fijidad, Jul 5, 2019.

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  1. fijidad

    fijidad Registered User
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    ...you don't have it at that particular moment when you try to horse a crown into the setting position.

    Is there some magic out there to remove a broken stem from a crown? Thanks, Dan

    stem.JPG
     
  2. gmorse

    gmorse Registered User
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    Hi Dan,

    If the stem is steel and the crown isn't, then a saturated solution of alum, (hydrated potassium aluminium sulphate), will dissolve the steel and leave the crown untouched. Warming the solution will accelerate the action.

    Regards,

    Graham
     
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  3. Al J

    Al J Registered User

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    I use alum all the time for this. Takes time but works well - just make sure that the solution stays in contact with the broken stem. If a bubble forms from the off gassing, it can sometimes insulate the stem from the alum solution so you have to be diligent about this.

    Cheers, Al
     
  4. fijidad

    fijidad Registered User
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    Thanks Graham. It may not be obvious, but these crowns (I found 7 that had the same problem) are soaking in a water/granulated alum mixture...and there are small bubbles coming from the area of the broken stem. I heat it occasionally with my alcohol lamp. I'm hopeful! Thanks again for the tip. Best, Dan

    Alum.JPG
     
  5. gmorse

    gmorse Registered User
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    Hi Dan,

    Depending on how concentrated the solution is and how warm it is, it could take hours or even days, but it will work in the end. Al's suggestion about agitating the bubbles away is well worth doing.

    Regards,

    Graham
     
  6. Uhralt

    Uhralt Registered User
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    This is a lengthy process and you will need your patience..
    Make sure that there is no oil or grease on the metal or the reaction will not even start. A bath in something like acetone before you start the alum is helpful. As already pointed out a hot, saturated solution of alum in water works best. I also add a small drop of hand dishwashing detergent and have the impression that it speeds things up a bit.

    Uhralt
     
  7. fijidad

    fijidad Registered User
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    I have a parallel process going on using white vinegar and water in a 1:1 solution; I've used this before to remove rust from steel, so thought I'd experiment. So far, the vinegar process is ahead of the alum.
     
  8. viclip

    viclip Registered User
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    I once destroyed an antique brass fountain pen body by soaking it in vinegar. It seems that acetic acid i.e. vinegar dissolves zinc, zinc being alloyed with copper to form brass.

    Therefore I'd be hesitant to use vinegar to dissolve any steel item contained in a watch part made of brass including crowns. While most brass crowns are plated or gold-filled, there are likely thinly protected areas in the hidden portions especially the threads.

    I don't believe that acetic acid at least in vinegar strength, will dissolve nickel but I've never experimented.

    Alum is readily obtainable in the spice section of most bulk food stores, canning supply stores etc. & is considered safe for both brass & nickel. And it's dirt cheap.

    Not very often mentioned, but a weak solution of sulphuric acid can also be used for dissolving steel parts out of brass or nickel components. I remember seeing a blurb to that effect in one of the old watch material catalogs although the company's name escapes me. I've also read about using sulphuric acid for the purpose in old watchmaking manuals. A good source of H2SO4 is old car batteries, lead particles can be filtered out.
     
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  9. Al J

    Al J Registered User

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    For me alum is the safest way, and time is not really a concern for me. I always have several watches in progress at any given time, so there's never a shortage of work to do while I'm waiting for the alum to do it's job.

    I've even used it to remove a balance staff...works very well:

    321Staff16_zpsftgueln3.jpg

    I normally cut them out on the lathe (I'm not a believer in punching them out, no matter what material the balance is or tools you use), but on this one I decided to give alum a try, and it worked great - staff after removal:

    321Staff18_zpsk94d41zg.jpg

    Of course not for balances with steel in them, but for those that don't, it could not have been easier. Zero distortion of the wheel or the hole, no risk of a slip and gouging in the lathe. So for people who don't have a lathe or might not be confident using it, this is a possible alternative to consider.

    Cheers, Al
     
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  10. fijidad

    fijidad Registered User
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    Experiment complete. After about a week in the alum solution, having heated it for hours at a time, the progress in removing the broken stems was very slow. There was no apparent degradation to the crowns...and very little to the stems. See the picture with the five crowns.

    Likewise no apparent degradation to the crowns in the white vinegar mixture...and the broken stems are completely gone. See the picture with two crowns.

    So, for me, vinegar was the much more useful of the two, with no damage in this particular case. Don't know how it would work in other cases, but at least for broken stems, I'll use vinegar.

    Alum.1.JPG Vinegar.JPG
     
  11. Uhralt

    Uhralt Registered User
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    Yes, acetic acid (vinegar) will slowly dissolve Zink, but so will sulfuric acid, even more so. Sulfuric acid is by far a much stronger acid than acetic acid. I would expect that the detrimental effect on the appearance of brass will be more pronounced with sulfuric acid compared to acetic acid.

    Uhralt
     
  12. Al J

    Al J Registered User

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    If the stems didn't dissolve after a week in an alum solution, then there's something wrong with the process you used. I never heat the solution and it only takes a day or two for me.
     
  13. gmorse

    gmorse Registered User
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    Hi Dan,

    My experience is exactly the same as Al's. The alum solution needs to be saturated and the agitation is important to keep the gas bubbles moving. I use a lab reagent grade, not the cooking ingredient sort, but I don't know how much difference that makes to be honest.

    Regards,

    Graham
     
  14. fijidad

    fijidad Registered User
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    I was wondering about that myself, having heard of others success at using alum. This was a spice I bought at Albertson's and was called granulated alum. Where would one buy the type of alum you've had success with?
     
  15. gmorse

    gmorse Registered User
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    Hi Dan,

    I bought mine online, from a laboratory supplies vendor.

    Regards,

    Graham
     
  16. viclip

    viclip Registered User
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    I use the Bulk Store variety of alum.

    I mix the initial solution then put it on one of those coffee cup warmers used by office staff at their desks (no risk of boil over). After the solution has been fully warmed up, I mix in oodles of additional alum. It's surprising how much alum you can dissolve in a nice warm solution.

    My first time, I needed to dissolve a large bow screw that had snapped off in the threaded portion. I was actually surprised how quickly the solution worked, albeit after I warmed it up & thoroughly saturated it.
     
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  17. Al J

    Al J Registered User

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    I also use alum bought at a bulk food store - this is potassium alum, the most common type. I don't heat the solution while trying to dissolve the steel part, but I do use hot water out of the tap, and mix in as much alum as the solution will hold, so it's a saturated solution. For stems making sure the solution is in contact with that small surface area is important, so making sure no bubbles for that keep the solution away, and also periodically cleaning out the black residue that will inevitably build up.

    I can't count how many times I've used alum in different situations. I like it because it's gentle and generally doesn't react with the parts I'm trying to save.

    Cheers, Al
     

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