Using Sherline lathe to remove riveted balance wheel

Discussion in 'Horological Tools' started by ChrisCam, Sep 13, 2019.

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  1. ChrisCam

    ChrisCam Registered User
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    Hi there are 2 main methods to remove a riveted balance wheel from its staff. There are arguments as always. Leaving that to one side the text book way is to use a lathe and with a sharp cutting tool remove the bent over rivet metal so releasing the staff. Obviously this is a risk for the inexperienced in damaging surrounding metal.
    Can anyone recommend a suitable cutter and / or give any tips for this procedure?

    regards
    Chris
     
  2. gmorse

    gmorse Registered User
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    Hi Chris,

    If you try and cut away the rivet on the collet side, it's very hard to avoid cutting into the wheel hub, because it's spread that end and you have to remove the spread part for it to push through.

    If you cut away the balance hub on the other side, you don't have to worry about the spread of the rivet. Cut to the red lines and it will push out in the direction of the green arrow. (The blue triangles are an exaggerated version of the rivet).

    Just make sure you've measured the hub diameter first!

    staff_dimensions_crop.jpg

    Regards,

    Graham
     
  3. Firegriff

    Firegriff Registered User
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    No mater which way you use start at your lowest rpm and work up or you will have a pretzel on a split balance.
     
  4. ChrisCam

    ChrisCam Registered User
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    Thanks Graham, are staffs seperated then used again? If so this method would be not appropriate but if so it looks a really good idea.
    Chris
     
  5. ChrisCam

    ChrisCam Registered User
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    By pretzel do you mean a twisted band or:???:?
    Chris
     
  6. gmorse

    gmorse Registered User
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    Hi Chris,

    No, once all the measurements have been taken, they're scrap.

    Regards,

    Graham
     
  7. ChrisCam

    ChrisCam Registered User
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    Thanks Graham, something tells me you've been doing watches for a long while!
    Regards
    Chris
     
  8. ChrisCam

    ChrisCam Registered User
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    Hi Graham, as ever been churning this over in my mind the method you suggest relies on getting right into the corner of the balance seat on the hub to remove metal from the staff, what kind if cutter can you suggest for this?

    Regards

    Chris
     
  9. gmorse

    gmorse Registered User
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    Hi Chris,

    Anything with a sharp tip and a somewhat acute angle; I can't give you part numbers for specific cutters because I do this with a graver!

    Regards,

    Graham
     
  10. ChrisCam

    ChrisCam Registered User
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    Thanks Graham, yes can't have a radius on the cutter or won't get the results. I am asking the guys on another machinist forum for their advice as to a suitable cutter. Other suggestions as to remove the staff I have found is partial removal of the metal rivet and then using the stake. I am open minded on this one because which ever way you go there is danger of damaging the balance wheel, so it is a case of which way in practice is least risky. As always several opinions that people are comfortable with. I am buying it a lot of old toot to practice with. As the balance wheel cross bar is recessed to accommodate the rivet metal would not a centre drill removing some metal on the Sherline lathe and then the staking tool be viable?
    Regards
    Chris
     
  11. gmorse

    gmorse Registered User
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    Hi Chris,

    The centre hole doesn't start off that way although it mostly ends with some taper from the riveting. The trouble is, you have no way of knowing how much taper there is and how deep it goes, so you'd be drilling blind. Better to use a method which allows you to see what's happening. You can take the hub down very accurately in full view with your setup and then use the staking set to push the staff out if necessary.

    Regards,

    Graham
     
  12. ChrisCam

    ChrisCam Registered User
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    Thanks Graham yes I get your argument. Removing the metal on the back to just leave a tiny washer then carefully remove that....without doubt it is the recommended way by the majority.
    Regards
    Chris
     
  13. ChrisCam

    ChrisCam Registered User
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    As an after thought I suspect the cutter to use on the Sherline will be the right hand facing cutter to acheive metal removal next to the balance wheel. on large items a parting tool could be used but definitely not one thinks at this micro level.
    Chris
     
  14. Chris Radek

    Chris Radek Registered User
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    Another thing to remember is that before you start cutting anything you must be positive you don't have a friction staff. Usually there are clues like the hub being a different color. A good study under the microscope before starting any job is a good idea.
     
  15. ChrisCam

    ChrisCam Registered User
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    Thanks Chris will there always be a little elevated hub above the balance wheel cross members if it is a friction fit? If not are there any other signs?

    Chris
     
  16. karlmansson

    karlmansson Registered User

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    #16 karlmansson, Sep 14, 2019
    Last edited: Sep 14, 2019
    Turning away until you only have a thin section of the hub left and then undercutting the hub will make a thin “washer” fall off when you have broken through to the balance. It’s worked for me before at least! But I’ve also only done it with a graver.

    In terms of tooling you would start with a turning tool and then change to a facing tool with an acute back angle and front face parallel to the axis of the work to cut a triangular groove into the remainder of the hub from the face of it. Just make sure that you start at a diameter that is smaller than the rivet or you’ll plunge into the balance.

    Regards
    Karl
     
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  17. ChrisCam

    ChrisCam Registered User
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    Thanks very much a detailed and helpful post.
    Chris
     
  18. Jerry Kieffer

    Jerry Kieffer Registered User
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    Chris
    Per your request.

    A staked balance staff can be safely machined from either side utilizing a Machine type Lathe and machining type procedures. For those who may not be familiar, machining procedures would not involve the use of a Graver but a tool post holding a lathe tool.

    Personally, I generally machine a staff from the Hub side unless I need the staff for measurement or other purposes. Since I have experience doing this, it is one of the few things that I machine based on visual observation in the same manner as Graver use rather than hand wheel settings.

    However, for beginning students I suggest the use of hand wheel settings until some experience has been gained as follows.

    (1) If machining from the hub side, I use a "AR" style brazed carbide tool per the first attached photo. The cutting tip is set so it is just touching the balance again the first photo and the carriage hand wheel calibration is recorded. When machining, the cutter tip is then brought no closer than .0005" to .001" of the recorded hand wheel setting. When the staff is driven out, the tiny amount that is left will harmlessly pop off.

    (2) If the staked side is to be machined, I use either a "E" or "D" style pointed brazed carbide Lathe tool set per the second photo. Again the cutting tip is positioned so it just touches the balance and the hand wheel calibration is recorded. At this point I move the cutting tip back and take a slight under cut on the staff per third photo.
    The cutter is then advanced forward taking a single cut up to the exact recorded measurement. Again, the very tiny amount left will harmlessly pop off when the staff is pressed out.

    A drop of cutting fluid is used on almost all metal machining procedures.

    At this point, I should point out that best results with a machine style lathe will depend on manufacturing suggested setup and calibration. On the other hand, anything less than the following for micro machining suggested or not, will place you at a disadvantage.

    The Gibbs should be adjusted loose enough so that even the very slightest movement of the hand wheels will cause the slide to move. Slightest movement can mean as little as the the thickness of a calibration graduation mark on the hand wheel scale. This in turn, will also allow micro tool feed back critical to safe use.

    In addition the Gibbs should be tight enough to prevent any deflection of the slide allowing for precise setting of the hand wheels. The ability to do this will depend on the design and quality of your equipment.

    Jerry Kieffer

    fullsizeoutput_420.jpeg fullsizeoutput_421.jpeg fullsizeoutput_422.jpeg
     
  19. ChrisCam

    ChrisCam Registered User
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    Jerry a really big thank you for taking time out to help once again.

    Kind Regards

    Chris
     

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