Sourcing or Making a Duplex Balance Staff

Discussion in 'Watch Repair' started by 4brokenow, Apr 18, 2020.

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  1. 4brokenow

    4brokenow Registered User

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    #1 4brokenow, Apr 18, 2020
    Last edited: Apr 18, 2020
    Let me just for-warn that I tend to be into self abuse when challenging myself to fix a watch. So keep that in mind as you read this.

    I have searched for a new old stock for a small New England Addison pocket watch I have. It’s a really nice example and would love to fix it but the staff seems to be near impossible to find.

    I have done pivoting of complicated staffs and have made staffs from scratch for very old, odd or English watches, but the challenge here is the slot on the staff. It is .2mm x approximately 1.2mm. Looks to have been originally cut with a wheeled cutter.

    The complications of the slot look to preclude me from pivoting it.

    I really don’t want to mess with getting another watch movement to harvest the balance as the likely hood of finding one reasonable that actually has a staff that is worth a damn seems like a slim chance. Seems once it’s a parts movement usually the staff is shot. And finding any whole running watch makes a guy feel guilty to consider for even a second cannibalization.

    Main question: Have any of you experienced craftsman ever made one of these? Is there such thing as a slot cutter that has a 1.2-1.5 mm diameter? Is there a practical solution to making a small slot cutter? Could it be made out of copper as a one piece disc and arbor and a diamond abrasive applied to cut the slot?

    Picture attached is the staff with a .22mm gauge pin for reference

    81EFA6D4-BECA-480B-911D-C8725B5B6DD7.jpeg
     
  2. Chris Radek

    Chris Radek Registered User
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    Is it two pieces? I think the part with the pivots and slot might come out of the hub.
     
  3. gmorse

    gmorse Registered User
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    Hi 4brokenow,

    I think this slot was originally cut with a very small milling cutter rather than a slitting saw, and Jerry Kieffer is the person to ask about this. In the absence of a mill, I guess a very small copper skive with diamond paste, as you suggest, might do the job.

    Regards,

    Graham
     
  4. DeweyC

    DeweyC Registered User
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    #4 DeweyC, Apr 18, 2020
    Last edited: Apr 18, 2020
    .
     
  5. 4brokenow

    4brokenow Registered User

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    Hi Graham

    Would be very interested to know what Jerry would have to say about this. We are fortunate to be influenced by someone of his level of talent.

    The slot is radiused across it’s longitudinal axis so it leads me to believe some wheel shaped cutter was used.

    One thought I had was to purchase a very small end mill at the 1.2-1.5mm diameter and then grind it into a slot cutter. Issue here is a end mill that small would be Expensive, especially as you can bet I will screw up the first attempt to fabricate one into a wheel cutter.

    Phil
     
  6. John Runciman

    John Runciman Registered User
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    Perhaps an unhelpful answer because I can't give you the reference I have seen a description of how to cut a duplex staff. The problem is which book would it be in I have too many books to look at. Then as far as the part that has the slit being separate if it was a Ruby version then yes that is removable. If you have Daniel's book on watchmaking he tells you how to make the Ruby part conveniently doesn't tell how to make the cheaper version. Then and one of the other books it talks about making the staff for the Ruby cylinder equally unhelpful.

    I don't suppose you did a search of the message board did you? I would skip over everything in the link below and just go to the very bottom I think you might find it helpful.

    Duplex Escapement
     
  7. Jerry Kieffer

    Jerry Kieffer Registered User
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    #7 Jerry Kieffer, Apr 18, 2020
    Last edited: Apr 18, 2020

    Phil
    First, thank you for the very kind words.

    With proper equipment, procedure and tooling, machining this slot with a Endmill is actually a very easy and straight forward project. Especially when considering the size is actually quite large in Micro Machining terms.

    This project can be done on either a Machine lathe or Milling Machine. Since you have not specified if you have a Mill, lets just assume you are limited to a Lathe. My personal procedure would be as follows on a machine lathe.

    (1) I would machine the portion of the staff on the end of stock that contains the slot slightly over size.

    (2) For Micro machining, I drill various size holes in various tool posts to hold center cutting micro boring bars using the lathe spindle to assure the hole is perfectly centered. However, they have
    become indispensable for many other uses such as this case.
    In this case I would transfer the previously machined stock above to a hole that it fits in a tool post per attached first photo. This assures that the machined slot will be perfectly centered.

    (3) When machining a balance staff, I harden and temper a blank to about 52 Rockwell hardness. Regardless of what is used, a staff blank will need to have some type of hardening tempering for
    exceptable pivot strength. When machining tempered material, the most practical tooling will be carbide or specified tooling for whatever is to be machined. In this specific case, I would suggest a center cutting 4 flute stub endmill such as TC54050 in the example link.
    TC58049 0.049" Micro End Mill 3xD Square End 4 Flute Uncoated, TC58249 0.049" Micro End Mill 3xD Square End 4 Flute AlTiN, TC52050 0.050" Micro End Mill 1.5xD Square End 2 FLUTE Uncoated, TC52250 0.050" Micro End Mill 1.5xD Square End 2 FLUTE AlTiN, TC54050 0.050" Micro End Mill 1.5xD Square End 4 Flute Uncoated, TC54250 0.050" Micro End Mill 1.5xD Square End 4 FLUTE AlTiN, TC54710 0.050" Micro Square End Mill 10xD Long Reach 5xD 3 Flute Unc., TC54713 0.050" Micro Square End Mill 15xD Long Reach 5xD 3 Flute Unc., TC54861 0.050" Micro Square End Mill 10xD Long Reach 5xD 3 Flute AlTiN, TC54864 0.050" Micro Square End Mill 15xD Long Reach 5xD 3 Flute AlTiN, TC56050 0.050" Micro End Mill 3xD Square End 2 Flute Uncoated, TC56250 0.050" Micro End Mill 3xD Square End 2 Flute AlTiN, TC53450 0.050" Micro Square End Mill Long Length 5xD 3 Flute Unc., TC53451 0.050" Micro Square End Mill X-Long Length 8xD 3 Flute Unc., TC53452 0.050" Micro Square End Mill XX-Long Length 12xD 3 Flute Unc., TC53632 0.050" Micro Square End Mill Long Length 5xD 3 Flute AlTiN, TC53633 0.050" Micro Square End Mill X-Long Length 8xD 3 Flute AlTiN, TC53634 0.050" Micro Square End Mill XX-Long Length 12xD 3 Flute AlTiN, TC57490 0.050" Micro 5xD Long Reach Mill 3xD 3 Flute Uncoated, TC57493 0.050" Micro 8xD Long Reach Mill 3xD 3 Flute Uncoated, TC57496 0.050" Micro 12xD Long Reach Mill 3xD 3 Flute Uncoated, Micro End Mills Square End Carbide - Carbide End Mill Store
    Four flute endmills contain more material thus stronger especially in stub length as required for this project. The most important part is the ability of the endmill to center cut that should be discussed with the supplier.

    (4) With the stock and Endmill mounted per first attached photo, the endmill is ready to engage the staff blank. At this point, it is extremely important that when a center cutting carbide endmill is used to take a depth cut into tempered material, that it be done in a very slow controlled manner. To assure a high rate of success, I typically replace the carriage hand wheel controlling the depth with a larger hand wheel for much finer control per second photo. The larger wheel control is such that, beginning students are able to master this work on their first attempt under these conditions in almost all cases.
    From this point, the length of the slot is slowly machined after each depth cut of about 1/3rd of endmill diameter. Cutting fluid is required for all procedures.

    (5) The stock can now be returned to the lathe spindle to complete the machining process.

    The third photo shows machining a slot with a .8mm endmill in 2.0mm diameter stock that I believe is slightly smaller than your project.

    Jerry Kieffer

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  8. 4brokenow

    4brokenow Registered User

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    Jerry,

    Thank you much for the reply. I had no idea that end mills were manufactured so small! I would never have thought to use the cross-slide in this manner to accomplish this task and on perfect center! I have a conventional 8mm lathe with cross-slide. I will have to fabricate a block to put in place of the lantern post. With your step-by-step and pictures I feel confident I can do this. I am going to shop for some end mills. I am going to need a .2mm (.007") end mill to do the work. It is a very-very tiny slot. I will update the thread as I go.

    Thanks Again!!

    Phil
     
  9. Jerry Kieffer

    Jerry Kieffer Registered User
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    Phil
    First, I should mention that the work piece sizes in post #7 are far to large to be representative of what you want to accomplish. For some reason, I was under the impression that the slot was 1.2mm wide that is several times larger than your goal. Regardless, the smaller size is no issue with the procedure as described. To demonstrate, I machined a .25mm slot in .45mm stock next to a .5mm ball point pen ball , since it only took a couple of minutes per attached photos.
    Sorry about the poor lighting on the quick photo of the slot.

    However, while nothing is impossible, a Watchmakers Lathe and Cross slide were never designed to utilize modern micro tooling in the same manner as machine tools that they are designed for. As such, you will be at a disadvantage, but I can make some suggestions once you are setup that may get you through a one time job.

    Jerry kieffer

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  10. Smudgy

    Smudgy Registered User

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    I made one of these on a watchmakers lathe before (also for a New England watch, and no, they don't seem to exist). My lathe has a milling attachment, which was needed. I also made the cutter from 0-1 stock, but if I were to do it again I would see if using a Dremel bit and narrowing it down to size would work or using Jerry's method with the end mill. Either way you will need something to act as a milling attachment. I also needed to use unhardened O-1 steel for the staff blank for cutting the slot (due to using O-1 steel for the cutter) and hardening/tempering before finishing the staff. It's not too difficult if you have the tooling and can turn a staff.
     

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