Expected diameters for screw plate dies (20 - 7)

Discussion in 'Watch Repair' started by RJSoftware, Nov 2, 2016.

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  1. RJSoftware

    RJSoftware Registered User

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    Hello all.

    I have had to order a new screw plate because I trashed my old one trying to get pieces of broken pivot wire out of them. Most times I have done this when trying to thread a winding stem that I turned.

    The problem is I am not understanding what is the expected diameters for the screw plate dies. Most importantly the 9 die (I assume 9mm). The dies are numbered 7 to 20 but no indication of mm or inch.

    The 9mm stem extension is the most used size for wrist watches. So that one gets used often.

    I have been doing this trial and error by small taper and guessing from there. I have considered running the same number labelled taps into same numbered screw plate die but I think I have read that destroys the die. But that doesn't really answer anything about the expected stock size.

    What are the expected diameters of stock sizes 7 to 20 on a screw plate?

    I don't really need the expected hole diameters or drill bit sizes to use for the taps but if that information should help could you please explain it's application to me.

    Both stock diameter for dies and drill bit sizes for taps in regard to sizes 7 to 20 would be a good thing to have as a sticky thread. Just saying...!

    RJ
     
  2. gmorse

    gmorse Registered User
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    Hi RJ,

    I suspect that any screw plate bought new today would be metric, so in your example, a size 7 would be 0.7 mm, a size 9 would be 0.9 mm and a size 20 would be 2.0 mm. The numbers marked on older ones such as Martin, (European), or Stubs, (British), were unique to each manufacturer, and in Martin's case, there were several different thread specs produced, as well as left-handed ones.

    You're right about not trying to screw a tap into the corresponding die; if you consider how the necessary clearances must work in the resulting male and female threads you'll see why this won't work.

    Regards,

    Graham
     
  3. RJSoftware

    RJSoftware Registered User

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    Hey Graham.

    I've been searching for some info on this and finding nothing. Was hoping there might have been a general rule like deducting 1mm from die size or maybe a table of diameter values to use.

    It's surprising because screw plates are common tool watchmakers use. Most have size 7 to 20.

    RJ
     
  4. Skutt50

    Skutt50 Registered User

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    I don't know if it helps but I have learned that to find the proper drill when making a hole for a screw is to take the diameter of the screw and deduct the screw pitch. E.g. to drill a hole for a 10mm screw with a pitch of 1,5mm would require a drill of 8,5mm.
     
  5. gmorse

    gmorse Registered User
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    Hi RJ,

    I came across this recently about the Martin plates.

    Regards,

    Regards
     
  6. praezis

    praezis Registered User

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    IMHO the first adress to ask about technical details should be your seller.

    Can you post a picture of the tool you are referring?

    Frank
     
  7. RJSoftware

    RJSoftware Registered User

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    Thanks Graham. I will give the following advice from your link a try.

    begin copy>>

    Sizes
    Saunier contains the following advice.
    For a long time we have made use of two Latard screw plates with holes of sizes such that a spindle which just passes into a hole of a given number will be of size most convenient for forming a screw in the next smaller hole.

    end copy>>

    So hopefully this rule of thumb still applies to the cheaper Chinese screw plates bought off the bay.

    I will let you all know.
    RJ


     
  8. RJSoftware

    RJSoftware Registered User

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    Hey Frank. It's a no name Chinese cheapo. $15
    RJ
     
  9. RJSoftware

    RJSoftware Registered User

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    Ok. Now I'm more confused, I think.

    Tried out some of my variety sized stock pivot wire. I got allot of different sizes. So I test the die holes for various different sizes and keep testing to find the smallest one that the stock would fit in, and then the next sized smaller die should be it.

    Well, didn't quite work out that way. Or maybe I am not sure. At first it seemed to.

    The stock pivot wire needed to be annealed/softened. I wrapped iron wire around them and heated them red hot one at a time while I was testing it out on my new screw plate.

    Just grabbing stock in no particular order and testing the diameter first to see which hole was last it would slide into.

    On a couple of them when I go to test the threading with the lesser sized die it slid through, so I chose the next smaller size.

    Then I got to thinking about how important it is to me that I can thread a stem as many repairs are broken stems that I can turn the remnant to accept a stem extension. I deliberately avoided #9 die as I want to make sure what I am doing is correct as that one is the most important for wrist watch repair. That's the most common men's watch stem size.

    Anyway, so to have a more systematic approach I decided to use my pin gauges and take down results. The pin gauge sizes graduate in very small amounts so there seems to be a spread on the results. I tried to pick the size with the most well formed threads.

    I had also slightly tapered just the tips and annealed them. The taper was to help pull in the stock to encourage cutting. Some would not start threading easily.

    I'm not sure the annealing of a few of my pin gauges was annealed/softened enough as a couple of die numbers (14 and 15) gave me trouble. I think the pin gauges are made of much harder material than the blued pivot wire.

    On the very small size (7) I managed to get threaded but the threads are faint looking. But oddly enough they do work.

    I managed to record some of the results but think maybe I toasted my 14 and 15 already. Not sure.

    I may try brass some time in future and see what values work best to produce the cleanest threads for each of the size die. One of my threads had real good definition but flat tops. My thinking is that that size stock was too big for the intended die.

    Please understand that this is initial trial results only. There does seem to be a pattern of a point 2 (.2) deduction of the die number. So maybe opposite of what should be...?

    On the 20 (biggest die) I made a guess that 1.8 would work and it did. Just got lucky.

    Oh and my digital caliper kinda sucks on the repeatability. If I squeeze harder I get different results. I try to be consistent in pressure and repeated each measure about 6 times. My pin gauges are in units of inches but easily converted by the caliper just not sure how accurate it is.

    rounded (actual)

    These are aprox .2 difference
    20 = 1.8 (1.78)
    15 = 1.3 (1.29)
    14 = 1.2 (1.18)

    These two are aprox. .02 difference maybe...
    10 = .88 (.87)
    7 = .68 (.68)

    Thing is too, that the formation of threads varied from weak to strong. So not sure I'm in the ball park yet.

    RJ
     
  10. praezis

    praezis Registered User

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    #10 praezis, Nov 3, 2016
    Last edited: Nov 3, 2016
    Hi RJ,

    this type?
    screwplate.jpg

    It is made in India like most cheap watchmaker tools. My wholesale catalog entry says 0.7 to 2.0 mm.
    I also use some Indian tools, but never would rely on their screw plates, remembering that European ones cost some 100$s.
    I know that steel quality and temper is not really existant with their tools.

    Frank
     
  11. gmorse

    gmorse Registered User
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    Hi RJ,

    I agree with Frank on this. I did try one of these once, but it was a dreadful thing and worse than useless. The threads were very poorly formed and irregular, and it was so soft that it barely cut brass let alone steel. There's a very good reason that they're so cheap! I have several Martins which are probably around a hundred years old, and they still cut very good threads.

    Regards,

    Graham
     
  12. RJSoftware

    RJSoftware Registered User

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    Thanks all. I do believe I agree. I will check out a better brand like Martin.

    Curious, when you guys turn stems from pivot wire do you anneal so you can thread?
    The Chinese plate screw dies really required it.

    RJ
     
  13. gmorse

    gmorse Registered User
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    Hi RJ,

    I'm not aware that Martin still exists as a company, although there are still a lot of their plates out there! Also, their thread pitches aren't metric. . .

    Annealing depends on the state of the steel to begin with; blued pivot wire often does need bringing down a bit, but if you go too soft, it can break off in the plate, especially in smaller sizes.

    Regards,

    Graham
     
  14. praezis

    praezis Registered User

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    RJ,
    why not buy a single die of good quality as you need it, one after one?
    Frank
     
  15. RJSoftware

    RJSoftware Registered User

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    I'm guessing the cost but really never gave it a try. I never see on ebay single watchmaker die maybe I'd start with 9mm.

    RJ

     
  16. gmorse

    gmorse Registered User
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    #16 gmorse, Nov 4, 2016
    Last edited by a moderator: Dec 31, 2017
    Hi RJ,

    For instance, a set of Wiru German taps and dies, with 12 sizes from 0.4 mm to 1.4 mm, (3 of each size tap typically), will cost in the region of £450 here in the UK. A Bergeon 2776-A set containing 8 taps and dies from 0.3 mm to 1.00 mm is around £400. Individual dies vary from £50 to £90, although some sizes appear to be hard to obtain. This puts the cheap Indian plates in context!

    Regards,

    Graham
     
  17. praezis

    praezis Registered User

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    From 1.0 mm upwards they are less expensive, about 25,- / die.

    Frank
     
  18. praezis

    praezis Registered User

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    In German, but how about this?

    Frank
     
  19. RJSoftware

    RJSoftware Registered User

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    #19 RJSoftware, Nov 8, 2016
    Last edited: Nov 8, 2016
    Well, I spent a little extra money for a better screw plate and I got the WIRU dies and handle too. The WIRU has not arrived yet but looking forward to it. The better screw plate is a Perrelet & Martin.

    While I am waiting on the WIRU I have a some questions on the P&Martin screw plate.

    First the numbering system goes backwards. So I am wondering if anyone knows what the sizes are that the numbers represent?

    It's the dangdest thing. Not criticizing just strange to me.

    It goes 0 to 17, so it is 18 holes, where 0 is the largest hole and 17 the smallest. AND it has two rows for each number. No screw cutting slots.

    I have already used it to repair one broken stem by turning down the business end who's threaded portion previously broke off and then threading it and adding a stem extension.

    I do not know for certain, but I suspect the second row is an alternate tpi (threads per inch). One row has the numbers next to it and then parallel to those is the alternate row. So if I am correct then you pick out a number and then choose which row you would like to use as to what tpi standards there might be to what region your dealing with (ex. American or Swiss).

    At first I thought maybe it was left hand vs right hand but it is not. I think not anyway. I sometimes get goofy results that seem to defy reality. So I hesitate to say with certainty. I had already run the stock in the numbered side. The diameter looked good but the tpi did not match. So I stuck those results in the alternate side to which some curls (cutting) did happen. As to the left/right, let's just say I would not be surprised if somehow I managed to produce some right handed threads with a left handed die somehow... But for now I will assume them both to be right handed. :)

    I already almost had a mishap with it as when testing out one of the holes the stock was slightly too big as I was not being careful enough and it broke inside. But it was easily extracted and no damage with a Dremel carbide bit that I had sharpened to needly tip and caught the center and then switched over to small Dremel carbide bit which extracted it. Glad of that. I ruined 2 Chinese plate screws already.

    I think you guys are right on the metal quality. It may be that all I needed to buy was this Martin plate screw but the WIRU is looking real promising.

    The WIRU has horse-shoe shaped dies and what I think is that if an emergency happens (piece breaks off inside) it might be that the die can be spread at the end with a screw driver to unbind it.

    It has a handle with a screw to maintain the die and I am also hoping that the screw is designed to squeeze the die more closed so that when it's in the relaxed state if a piece where broke off inside then it may be removed without having to wedge and open it. That would be nicer..!

    That would pretty much be a real close design as to what I was talking about before with a die that would be adjustable to different stock sizes. I still like my idea better as then one could choose tpi to suit a desired diameter. Taking into account the effect of threading to the diameter.

    Anyway, I am going to establish whatever I can in regards to this matter. I hope to make a complete and thorough chart of the expected diameters as I know that I will need it in the future.

    I also believe that there may be no need to soften the blued steel pivot wire. It seems to cut ok as long as the diameter is in agreement.

    About the method of selecting stock diameter by inserting in adjacent larger die hole till stock would just fit in and then threading that in the objective/desired smaller die next in line. I found when using the pin gauges a bit of uncertainty.

    The Chinese screw plates are listed under Jewelers also so it may be that they are only designed for softer metals. I think they are for ear-ring post maybe. Brass or gold...

    When I was using the pin gauges there was an overlap as more than 1 did fit. Because what I would find that when inserting in the size larger that would finally be large enough to barely fit that stock would sometimes slip past when attempting threading in the objective/desired hole. The stock was too thin diameter to thread properly but almost started to thread. So the fitting by snug feel was not exactly perfect.

    So it had to go next size up on the pin gauge. My results varied but that may be due to the Chinese dies wearing out. So I have uncertainty.

    The results where mixed up and varied so I need to do this over with the better screw plate dies. But this brings to me concern over the small graduations of the pin gauges may produce overlapping (more than one) diameter. A range of diameters per the die. Where I would have to choose the diameter with the best results.

    Where tips would be shallow (beginning to cut) to good form (perfect ) to flatten tops (stock too large). But these are the results I got from the Chinese screw plates. Two of the dies did not survive (14 and 15) and failed to cut anymore. Probably from the over-sized pins.

    I imagine that it might come to others as intuitive to not have threading to squeak. That stock begins to squeak from too tight a fit. I used oil also. But could tell when the stock begins to bind from the clicking type of squeak. I do turn back and forth and after a couple of revolutions remove and blow out shreds. Then return to do more. I have notices in some instances no squeak at all. Probably more ideal conditions. But threads then looked too light.

    I used the stem extension to compare threads against under the scope and I notice the threads they have are much more sharp and clean. It would be nice if my results where the same but I really only care if it is functional.

    I'm not exactly sure if the second row produced the correct tpi but it was a close enough result that I went ahead and used the stem extension. It resulted in a tight fit anyway. The stem extensions do tend to crack easy especially when the diameter is a touch too much.

    I may have to establish each tpi with each expected diameter for each hole of the Martin plate I just got. Only thing is I may be dealing with different standards from different countries and all I have is thread gauges from American system. I wonder if it is still acceptable to define them in American system terms only.

    RJ
     
  20. gmorse

    gmorse Registered User
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    #20 gmorse, Nov 8, 2016
    Last edited: Nov 8, 2016
    Hi RJ,

    The Wirus are the real business, and are properly hardened and tempered tool steel. If the dies are the split type, then the right holder for them will have a screw with a conical point which fits in the slot, which will open the die slightly, and one each side of that which will close it, (as long as the centre screw is out of the way).

    Martin screw plates will be marked with a "G" (for gauche) if they're left-handed, "L" for Latard, and "B" for Bourgeaux. Some of mine have just threaded holes, which don't so much cut a thread as force the metal and distort it into a thread, some have a set of cutting holes, (with one or two relieving holes next to the tread to form a cutting edge), and a set of non-cutting, some have two sets of cutting holes, but they're always in the same series and with matching numbers as far as I've found. The web pages here and here explain more. Your Perrelet & Martin are "Latard" type.

    It's a good idea to back out the die for a quarter of a turn or so every turn, (or even more often, you have to get a feel for it), so that you don't get a build up of swarf which will jam and cause breakage. The correct size of stock is even more critical with the thread forming plates than it is with the thread cutting ones.

    From my experience with the Oriental plates, they're so soft, and the threads are so poorly formed, that even on brass they produce bad threads. Given that, trying to match up sizes is pretty useless.

    Regards,

    Graham
     
  21. RJSoftware

    RJSoftware Registered User

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    #21 RJSoftware, Nov 8, 2016
    Last edited: Nov 8, 2016
    Hey Graham. Have you established any useful diameters for the plates that you have? If so lets see hey...!
    (or do you have a method like the larger die before destination slip/fit trick?).

    Thanks for links. Much appreciated. Mine has the L for Latard. I think mine is the no cutters thread only force to conform type. Hey if it works...!


    On the Latard chart it has Size (20 ) Diameter (0.367) Pitch(0.087) could it be a simple as adding the diameter and pitch to get the expected diameter of the stock to use?

    No, I don't know what I was thinking (need coffee), pitch is the distance length between threads. So I got no clue.

    RJ
     
  22. gmorse

    gmorse Registered User
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    #22 gmorse, Nov 8, 2016
    Last edited by a moderator: Dec 31, 2017
    Hi RJ,

    It's a good place to start, but the suggestion from Skutt in his earlier post about the relationship between diameter and pitch also makes some sense. I've never measured the thread angle in Martin screws, but it looks to be about the same as BA, which is 47.5°, so at these relatively small sizes it's not an unreasonable approximation.

    I tend to try the screw I'm replicating in the Martin plate, and choose that or the next size larger if the original screw is at all loose.

    Regards,

    Graham
     
  23. RJSoftware

    RJSoftware Registered User

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    Hey... that's right. The Martin plates don't have cutters so one can test fit an existing for the correct choice of die. I almost want to say the only thing left is to turn the stock to the size of the next larger die (snug fit test). I will give it a go.
     
  24. dshumans

    dshumans Registered User
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    I believe this may be what you are looking for. My Bergeon tap & die set has a label that lists the screw diameter, the pitch, the diameter of the shaft before threading and the diameter of the hole before taping. See the 4 columns of the label (the bottom header is in English)
    Bergeon Label.jpg Bergeon Tap & Die.jpg
     
  25. RJSoftware

    RJSoftware Registered User

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    Hello dshumans.

    Yes this looks very promising. I hope I am perceiving it correctly.

    The symbol of the circle with the line across I take to mean diameter.
    So the first column I take to mean the results. I will call this column A.
    The second column is pitch.
    The third is the paydirt, the expected diameters. This I have labelled column B.

    So here is the info in a new table.

    for RESULT A use DIAMETER B in mm

    A B
    .30=.26
    .35=.31
    .40=.35
    .45=.40
    .50=.44
    .55=.49
    .60=.53
    .65=.58
    .70=.62
    .75=.67
    .80=.71
    .85=.76
    .90=.80
    .95=.85
    1.0=.90
    1.05=.95
    1.10=.99
    1.20=1.09

    Sincere thanks
    RJ


     
  26. praezis

    praezis Registered User

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    With a little bit of arithmetic, you can also say:

    diameter of the raw bolt = thread diameter x 0.9
    diameter of the hole before threading = thread diameter x 0.8

    Frank
     
  27. RJSoftware

    RJSoftware Registered User

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    Hey Frank. Well I was hoping for a simple solution like that but the numbers are off.
    Do you say that calculating the width as 90% works, -you have tried it?

    We deal with such small parts, it's hard for me to believe it's not critical difference.
    But if it works...!

    RJ


     
  28. praezis

    praezis Registered User

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    Off by not more than 0.01mm! Congratulation if you can drill or make bolts with errors < 0.01mm!

    Frank
     
  29. RJSoftware

    RJSoftware Registered User

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    Ah ok my bad. I'm use to the thousandths of inch world. I keep forgetting mm is much smaller.
    Yes I see you are correct, 90% it is then.

    Nice and simple....! :)

    RJ

     
  30. dshumans

    dshumans Registered User
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    Not only that, but Bergeon says that different metals may utilize slight changes from these numbers. More malleable metals like gold can start with a slightly smaller hole or larger shaft. It is also interesting to note that while the screw hole is tapped from a hole diameter smaller than the finished piece, indicating a purely cutting action, the screw shaft starts out smaller than the finished screw, indicating substantial forging during the die cutting process to make it larger than it started. Before I knew this, I tried to cut screws from blank shafts of the final size diameter thinking it was all a cutting process, and broke off some shafts even with tap lube.
     
  31. RJSoftware

    RJSoftware Registered User

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    Yep, me too..! Kind of counterintuitive as you stick a smaller stick in a hole and it comes out larger... well, that might have sort of sounded like a dirty joke but anyway... :)

    RJ

     

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