Broken mainspring abour

Discussion in 'Clock Repair' started by Beer o'clock, Dec 9, 2017.

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  1. Beer o'clock

    Beer o'clock New Member

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    Hi, I am a beginner and I need a little bit of advice. I am trying to repair a Seth Thomas number 89 movement. I dismantled and cleaned the movement however on trying to engage the main spring back onto its arbour I managed to break the arbour.

    This occurred no doubt to me applying to much tension with my home made mainspring winder! I would like to replace the arbour, ratchet and first wheel as one assemble simply because I have no idea how to remove the ratchet and first wheel off the arbour. I think I am in enough deep water already!

    Is there anywhere I could purchase this assembly, first wheel, ratchet and arbour so that I can just reattach the mainspring? Second hand or new is fine.
     
  2. roughbarked

    roughbarked Registered User

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    What you probably need is a donor clock movement.
     
  3. kinsler33

    kinsler33 Registered User

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    See if you can post a few pictures of the broken part and the ST movement itself. The people who read these posts are exceedingly skilled and clever, and may be able to help you get around this particular misfortune; but they'll need to look at a picture or preferably several.
     
  4. bikerclockguy

    bikerclockguy Registered User
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    That's a pretty common movement, and as the others said, you should be able to find a movement/parts pretty cheap. I bought a whole bag of Sessions parts from 3 different clocks for 10 bucks a couple of months ago on eBay. I'd try there first, just type Seth Thomas 89 in the search window. If it were a Sessions, I could fix you right up with a main wheel, but I don't have any extra Seth Thomas parts
     
  5. lpbp

    lpbp Registered User
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    Seth Thomas 89 is a fairly common movement, but in comparison to other like mantle clocks it's not cheap, and the movement you buy online might be worse. Show us a picture of the wheel you have and we may be able to help.
     
  6. roughbarked

    roughbarked Registered User

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    Another possibility is that if you cannot afford a movement to fix the problem is that you try to find other ways to fix it. It may be but don't quote me because I have never tried, that other Seth Thomas arbors are close enough to adapt to fix. The serious problems that arise here are that they aren't easy to remove and replace. Essentially it would be best to seek a wheel/arbor unit which can replace the broken one. Without pictures though, nobody can reaslly assess the problem in its entireity.
     
  7. Beer o'clock

    Beer o'clock New Member

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  8. Beer o'clock

    Beer o'clock New Member

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    These pics show the broken arbour compared to the other good mainspring arbour. The missing length is about 12mm (1/2 an inch).
     
  9. roughbarked

    roughbarked Registered User

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    This may well be repairable. The bond will need to be strong but the key will also need to travel the whole length of the available square you see before a repair is executed. It will be less stressful on the repair if the key also connects with the original part of the square. That being said, The new length of square will need to be securely connected to the remaining square. There are different ways to do this and you will need to measure the confines of the case in regard to this.
     
  10. David S

    David S Registered User
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    Without having it in my hand to confirm. I think I would treat it like a repivot. Chop the arbour off at the shoulder, bore it out and insert a new square complete with the bearing surface.

    David
     
  11. wow

    wow Registered User
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    I may have a complete unit in my bone pile. PM me if you are interested.
     
  12. shutterbug

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    I like David's suggestion the best, if you can't find a replacement part.
     
  13. R. Croswell

    R. Croswell Registered User

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    I did a couple similar repairs last year using David's method. I used a lathe and small boring bar to bore the hole for the new "pivot" which must be pretty true and on center. I used 609 Loctite and then cross-drilled and fitted a pin to make sure it was strong. worked out well. Some years ago I did one and used just Loctite, failed, soldered and failed again, pinned it and has been fine ever since. There's a lot of torque there. I would not attempt to weld the broken part back on unless you are an expert with lots of experience welding tiny parts like this. A replacement part or course would be the easiest repair. If you replace the entire assembly please make sure the ratchet allows the arbor to wind the right way! .......don't ask how I know that you need to check this.

    RC
     
  14. David S

    David S Registered User
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    I didn't state the retention method, but definitely I would have used a cross pin as RC mentioned.

    David
     
  15. Jerry Kieffer

    Jerry Kieffer Registered User
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    As others have mentioned, you should not have a problem finding a replacement that would be preferable.

    However, If you are unsuccessful finding a replacement, a competent repair person can successfully repair this arbor.

    My personal method of repair is as follows.

    First, my personal standard is that any repair should have the original appearance and equal or exceed original strength.

    My first consideration is that the cross sectional metal to metal contact (Shearing contact area) of both the arbor and repair part should exceed the original assembly. While pinning is often utilized in Horological repair, I do not cross pin anything requiring this amount of torque. When cross pinning is relied upon for strength, it will reduce the metal to metal contact area, thus reduce the torque required to shear the pin in comparison to the original strength. In addition, it is a visible repair.

    To resolve this issue, I drill the arbor and thread the arbor/work piece with a very fine thread. While I do not have the arbor in hand for sizing, I have often used a 3/16" by 80 TPI tap and adjustable die for this type repair. The adjustable Die is used to produce a tight thread to thread fit required with fine threads. If this thread were used, it would take about 15 threads to equal original shear strength over a length of about .200" of length even though I would use at least twice that if space permitted. This repair also produces an invisible repair.

    Standard threads remove to much metal greatly reducing the strength of both the work piece and original arbor. It would not be advisable to utilize them for this type repair.

    The attached photo shows the difference between a standard 32TPI thread and a 80 TPI thread on the same diameter.

    Jerry Kieffer

    fullsizeoutput_19c.jpeg
     
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  16. R. Croswell

    R. Croswell Registered User

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    If the insert is secured first with an appropriate retaining compound the shearing contact area is greatly increased, within the limits of the compound's shear strength. If the hole for the cross pin is chamfered and both ends of the pin peened and filed or turned down the repair can be invisible or nearly so. Some manufacturers, notably Ingraham secure the ratchet wheel with a steel pin cross-pinned through the arbor. If the pin is of suitable size there will be more than enough strength to prevent a repair failure. Like so many horological repairs, there is more than one way to do a repair like this depending on available tooling and one's skill level and outcome objectives.

    RC
     
  17. David S

    David S Registered User
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    Absolutely! The double shear strength of a pinned connection is more than adequate for this application. Agreed it won't be invisible, if that is important to the OP.

    Now what if the break had of been for the other arbour. I have searched for a 3/16" x 80 left hand tap and die and haven't found one so far. I am sure there is one.

    David
     
  18. Jerry Kieffer

    Jerry Kieffer Registered User
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    David
    If the pin is to small it of course will shear. However, if it is large enough to provide adequate shear strength, the hole provided for the pin will greatly reduce the cross section of metal provided by the original condition. At this point, the weak spot will be in the area indicated on the sketch below. The pin will actually assist in separating (Pushing apart) the inserted work piece under high torque if and when one side of the pin cracks.

    In regard to taps and dies, I should have mentioned 10 X 80 that is virtually the same thing and is far more common. I doubt a left hand 10 X 80 or others will be listed on the internet, but are available by asking in the right places. At any rate, whatever is needed most of the time will not be commercially available. So those who have carefully selected their Lathe will simply single point cut what ever oddball OD and TPI is needed right or left hand. Single point threading option has many uses and once incorporated in your daily routine, it becomes just another simple procedure.

    Jerry Kieffer

    fullsizeoutput_1a0.jpeg
     
  19. R. Croswell

    R. Croswell Registered User

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    If the pin is about the same diameter as the pin through the arbor that holds the inner coil of the spring, or the pin that holds the ratchet wheel, and the pin is a good fit there won't be any problem. I, and others I feel sure, have seen the square on the arbor wring off before the spring or ratchet cross pins fail, which appears to have happened in the case we are discussing. I would argue that the best "repair" would be to machine a complete new arbor. Neither threading or pinning was used in the original construction and neither method returns the clock to original condition.

    RC
     
  20. Jerry Kieffer

    Jerry Kieffer Registered User
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    RC
    Each would need to be evaluated based on its construction. The holes that you refer to are typically in a section of the arbor that is much larger diameter than a repair insert. It is the smaller diameter insert weakened by a hole in it that is the problem area while receiving maximum torque.

    If an invisible repair can be made that is equal in strength and function to the original part, there is no reason not to do it if its the road of least resistance.

    Jerry Kieffer
     
  21. R. Croswell

    R. Croswell Registered User

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    We are talking about a Seth Thomas # 89 pictured in post # 7, which should be familiar to anyone who has fixed many American clocks. The arbor with the pin that that secures the spring is no larger than the part we need to repair and the load on the spring holding pin is only on one end of the pin and therefore twice a great a shear load as for the cross-pinned repair where the shear load is shared by both ends of the pin, all else being equal. But all else isn't equal. The method suggested used a snug fitting insert secured first by Loctite retaining compound which adds considerable shear strength to the repair due to the significant bonded surface area. If the cross-pin is installed as described - the holes in the arbor chamfered and the ends of the pin peened or riveted - then the pin will also be under tension which will which will increase the contact pressure between the arbor an the insert. The insert is constrained by a snug fit in the outer part of the arbor, and being made of a machinable steel, there is little opportunity for the part to crack. The only way to prove the maximum strength of either repair beyond speculation, unfortunately, is destructive testing to the point of failure. With either the threaded or pinned repair I suspect the weakest point will be at the base of square section, not the repair. With either method it is important that the bearing surface and the winding extension be true and straight. Unless one is equipped to lathe-turn the fine inside thread, I suspect most individuals will have difficulty hand-tapping that shallow hole, and threading the insert accurately enough to have the finished part run true. Of course the finished part can be turned true, but unlike a pinned insert which can't move, there is the potential for a threaded part to shift under loading. Even though a fine thread reduces the diameter of the part at the root of the thread, it does none the less reduce the diameter and creates a potential fracture point where the thread ends. Truth is that neither repair will have 100% of the strength of the original part, or of a complete new part machined from a single piece of metal. Therefore according to your own standards, neither of the suggested repair methods is acceptable.

    I believe that we are, or should be, more about describing various repair methods that have actually been used successfully to repair similar damage than declaring that this or that is the best or only way. In most cases there is more than one way and the "best way" is often dependent upon the tooling one has available and one's skill level and ability to properly use available resources. The outcome objective is in the end what determines which method(s) can achieve that objective. One then has to ask, can I do that? If not, what is "plan B"? In this specific case, a replacement part, as already suggested, may be the best plan but if one is not available, then the OP has at least a couple other options to consider.

    RC
     
  22. David S

    David S Registered User
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    I find this an interesting thread. With all the discussion regarding required strength I decided to see the maximum torque I could put on a typical winged key with my fingers like if I was really forcing a key. Now with my hand, and some arthritis I got 5 lb-ft.

    I wonder what others can do?

    At least this would tell us the shear force at the pinned joint, and that could determine the minimum diameter steel pin without press fit or adhesive.

    David
     
  23. Jerry Kieffer

    Jerry Kieffer Registered User
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    RC
    The weakest point of any metal repair such as this is rarely rocket science. It will almost always be the point that contains the least amount of metal. In this case, the Inserted section should be slightly larger, than the exposed square making the square section the weakest part as per original. That is unless you drill a hole in the inserted section reducing the surface area at a particular point to less than that of the square section. Easily observed visually in most cases.

    For threading, the fine thread is used so that from the bottom of one thread to the bottom on the opposite side will have greater surface area than the square section making the square section the weakest point again per original. Thus duplicating original strength. Of course the threaded section is threaded so that it bottoms out in the arbor thus preventing any movement.

    You do bring up a good point in regard to threaded alignment.

    However, this is of no issue what so ever, if one spends their time attempting to improve their skill level and quality of workmanship on a daily basis, rather than looking for excuses and methods to just slide by.
    Hand tapping a hole or work piece requiring alignment will almost always turn out even worst than you indicated. Those who research sound metal working practices, will find that after drilling the hole in the arbor they can place the tap in the tailstock chuck to tap the hole. This will hold the tap in perfect alignment with no skill involved per the first attached photo.
    The Insert on the other hand will be in the reverse. The die will be held in the Lathe Chuck and the work piece in a tailstock chuck again providing exact alignment per the second photo.

    Jerry Kieffer

    fullsizeoutput_1a1.jpeg fullsizeoutput_1a2.jpeg
     
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  24. David S

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    Indeed the weakest point is not rocket science. For me the point is whether a pinned joint will be strong enough to provide a reliable repair, even though it may be not as strong as the original.

    As an effort to try and determine what may be required, I have performed a test to see what sort of torque I could impart on the arbour with a winged key and ordinary hands.

    It would be nice if others could try and give us some figures.

    David
     
  25. R. Croswell

    R. Croswell Registered User

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    There is no argument that the weakest part of the original part is the square section as evidenced by the fact that we often see these twisted and/or wrong off. I believe that either the threaded insert that you describe or a properly executed pinned insert with a riveted pin augmented by a chemical retaining compound, will provide adequate strength for normal use and either method will likely exceed the strength of the square, but the success of either method will depend of the individual part and how well the repair is done. Unfortunately one can only know the breaking point of an individual repair by destructive testing. My original point however related to how the repaired part compared to the original part in its entirety which is perhaps of more concern to some than others. As you stated, the weakest point of any metal repair will almost always be the point that contains the least amount of metal, and it should also be obvious that there is less metal at the base of the threaded portion than in the solid portion. Considering the total part, the repaired part is not equal to the original part in strength, plus the original part did not have a screw-in winding arbor (or a pinned arbor either) which is a departure from the original design. I have successfully used the pinned repair multiple times, and I have no doubt that the threaded insert will also produce a sound repair, I still maintain that neither repair completely meets your self-imposed standard of "equal to original". The highest standard for this "repair" is to duplicate the original part in one piece from the same type of material and to the same dimensions as the original part. The two methods we have described both require the use of a lathe for any reasonable degree of success, and of course if one has a lathe one also has the ability to replicate the original part. Which brings us full circle back to finding a good replacement part being the most expedient way to restore the clock to the way is was originally.

    I'm sure some will benefit from your illustrations on threading with tap and die using a lathe as a guide, thanks for sharing that.

    RC
     
  26. shutterbug

    shutterbug Moderator
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    Jerry - I've never used the lathe to tap. I always assumed that the tap was pretty much self aligning. I'll have to rethink that! Thanks!
     
  27. David S

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    If you are preparing a part to be tapped in the drill press or the lathe and have already drilled the hole, you can also use a "tap follower" to keep the tap true while starting. This is used with hand tapping. They are a simple spring loaded center that fits in a dimple feature in the end of the tap or tap holder. They are easy to make as well.

    Regarding this interesting discussion regarding strength of various repair methods, I was hoping folks would start more quantitatively. Starting with the expected max torque during use. and then proceeding to do some calculations to determine what options make sense.

    There are basic engineering calculations that can be done to determine if a pin will shear for example based on the expected load. we can always verify by destructive testing, but it isn't necessary to get a first order feel for strength of the joint.

    David
     
  28. Jerry Kieffer

    Jerry Kieffer Registered User
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    RC
    An arbor repair would only be made where a replacement was not available or where a portion of the arbor is retained to retain value. Of course it could also be a time or convenience thing.
    Again, you missed my explanation for using a fine thread. For example, For a arbor containing a common 4mm winding square, the square itself would be about .150" across the flats. In this case, I would typically use a .187" (3/16") inserted section typically containing a 80 TPI thread with a thread depth of about .006"-.007". When I subtract the thread depth I end up with a section that is about .173" in diameter that exceeds the strength of a .150" square. If I utilize at least 15 tight threads (Generally use at least twice that) the repair will equal the original in strength. If a repair is to be made on this type item with its history, anything less than original strength would not be worth the effort in my opinion. However, I have a question? If you were inserting a .187" work piece into a drilled arbor to repair it, what size pin would you use?

    Shutterbug
    Attempting to thread anything straight with a Tap and Die will most likely end up being a "get lucky" proposition at best. Many times it is not a concern, but in other cases it can be an absolute necessity. Over the years, I have been asked to do many types of repairs. One repair where this method using the lathe has really shined is as follows.

    If you do repairs and you have not been approached by toy collectors, you probably will in the future. One of the common repair requests is to replace damaged or deteriorated wheels on various toys. However to retain value, any repair must be invisible. Reproduction wheels can be aged but that is not the issue. The issue is the axil that often has those half round knobs on each end that I understand were spun formed at the factory. If one of these are removed and replace the wheels , how do you replace it.
    Since they almost always have excessive end shake, I saw the axil in half in the middle with a thin blade jewelers saw. I then face/spot/drill/ tap each half in the Lathe. Then the two half`s are then screwed together with a short threaded piece in the center to an invisible joint when tight per attached sketch.
    While only occasionally used,this procedure has been a life saver over the years, but not possible without a accurate capable Lathe.

    Jerry Kieffer

    fullsizeoutput_1a4.jpeg
     
  29. BLKBEARD

    BLKBEARD Registered User
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  30. Jerry Kieffer

    Jerry Kieffer Registered User
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    My illustration of threading with taps and dies on a lathe was only to demonstrate a point and is far from the whole story. While spring loaded tap guides are certainly a more accurate method of tapping a hole than by hand, they are designed to be used in a tapping guide with larger common taps used in general construction.
    To make a long story short, with the smaller threads used in Horology, direct mounting in accurately aligned lathe chucks offers greater efficiency and control. In addition, the assemblies used with tapping guides are often to long to be used in small Lathes.

    Jerry Kieffer
     
  31. BLKBEARD

    BLKBEARD Registered User
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    I've seen many YOUTUBE Machinists fabricate their own Tapping Guide/Tap Follower rather than buy a factory built one.
    I've seen many of the specialty tools, fixtures and widgets you've made.
    Certainly an accomplished Micro-Machinist such as yourself could make a scaled down version, should you choose to do so.
    And there may be a small one commercially available, I've never checked.
    My Father was a Machinist. (He passed away in June) I have 3 or 4 of his. I need to make an adapter for one of them, to be able to use it with hand taps that have a point on the end instead of a divet
     
  32. R. Croswell

    R. Croswell Registered User

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    No, I did not miss your explanation, nor did I imply that it wasn't an acceptable way to repair this damaged part. I think you missed my point that a part repaired thusly is not as the original part in design or strength which seems to be your self-imposed standard for excellence.
    I believe I answered that question earlier. Keep in mind that if the arbor is not going to be threaded then the insert can be made larger. I'm sure we won't agree, so I hope we can at least agree to disagree. The OP has at least three options that can work and I don't believe I can add anything more to this discussion.

    RC

    [/QUOTE]
     
  33. Jerry Kieffer

    Jerry Kieffer Registered User
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    As mentioned, its a long story that I will try to make as short as possible.
    First, for those who have a interest, you can google "Tap Guide" and "Tap Wrench". This will give you a clear picture of what is being discussed under "Images".
    Let me just say that gadgets can be useful, are also often a marketing ploy. Each must be carefully evaluated for each application.

    The Job at Hand
    For this specific job, a centered hole will need to be taped with a fine thread that is aligned with center rotation. One must also keep in mind that you only get one shot at this.


    Using a Tap guide and Tap wrench in a Lathe

    To use this setup, I would first put the spring loaded Tap guide in the Tailstock Chuck. I would then insert the 10x80 tap into the "T" handled tap wrench. This is where the issues start.
    A typical tap of this size will have a short square for mounting that is about .150" across the flats and about .200" long. When mounted because of the short flat and "T" wrench construction, the tap will rarely run true in the wrench. Again because of the short mounting, it can be moved to appear to be aligned, but the mounting is not rigid enough to remain in that position during use.
    Setup for use, we would first have the tap guide that would engage the back side of the tap wrench and the tip of the tap engaged in the arbor hole. Under spring tension and unstable mounting of the tap will almost always create some type of "Bow" in the system during use. The result will typically be a tapered thread to some degree that will prevent the fine thread from seating properly and greatly decrease thread strength. This of course would be of no concern when using larger course threads for general construction.

    Using the Tailstock chuck to hold the Tap

    After the hole is drilled, the Tap is inserted into the chuck. In this case, the tap is held over the length of the tap shank providing a very rigid and secure mounting that is aligned to rotation.
    The tailstock lock is then tightened loose enough so the tailstock can slide but snug enough for accuracy similar to the adjustment of Lathe and Mill slides. From this point the tap is moved up to engage the work piece and the lathe chuck is turned by hand rather than a the Tap wrench. This assures a straight aligned thread each and every time.

    Jerry Kieffer
     
  34. Jerry Kieffer

    Jerry Kieffer Registered User
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    #34 Jerry Kieffer, Dec 14, 2017
    Last edited: Dec 14, 2017
    [/QUOTE]


    RC
    My standard for all repairs is that the repair at least equal the strength, appearance and function of the original.

    Under proven industry standards, pins are used for positioning, light torque and shear pin applications. Where maximum strength is required in round stock, threads and splines are the standard. However, it is not important on what we agree on or not agree on. What is important with a discussion like this, is the value of evaluating each and every procedure before performing it.
    In this case there is more than enough to do that.

    However, there is one thing you forgot to add.

    How would the average person cross drill a small hole to the centerline of a small round arbor less than a 1/4" especially if there is a large wheel next to it ?

    Jerry Kieffer
     
  35. David S

    David S Registered User
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    Dec 18, 2011
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    It seems like RC has moved onto better things, but regarding cross drilling a hole as has been asked. First and foremost to execute this repair with a cross pin, the hole doesn't have to be exactly on the centre line. So just clamp up arbour and file a small flat on the shaft. Give it a punch mark > select the bit of choice and go for it. Done it many times in the old days, even though today I would do it differently.

    David
     
  36. kinsler33

    kinsler33 Registered User

    Aug 17, 2014
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    I have a friend who does some fairly amazing welding, having learned it well enough to be certified for nuclear power work. There are so many new methods of welding that I'm not at all certain that this wouldn't be the most practical method of repairing this arbor. Maybe even silver brazing would be sufficiently strong. So it might be worth hiking around to a specialty welding shop and having them take a look at it.

    I've never seen an arbor broken on the square section like that.

    M Kinsler
     
  37. Jerry Kieffer

    Jerry Kieffer Registered User
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    David
    Not the answer I would expect from you.

    In Horology there are times when cross drilling to the exact center line is desirable or even required. A Milling Machine is the preferred method but if you only have a Lathe, no issue.

    For the benefit of Beginners, the following is one method on a lathe

    (1) A short stub of square stock can be mounted in the tool post and spot drilled/ drilled to a work piece diameter per the first photo.

    (2) The tool post is then rotated 90 degrees and the work piece inserted in the hole to the desired position per the second photo.

    (3) The square stock his then spot drilled/ drilled with the work piece in the desired location. This will ensure an exact center line drilled hole each and every time.

    Jerry Kieffer

    fullsizeoutput_1a5.jpeg DSCN8289.JPG
     
  38. David S

    David S Registered User
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    Jerry,

    Like I said, today I would do it differently either in the mill or lathe as you suggested. But you asked specifically about the short protrusion to work with. I am trying to suggest things for folks that don't have a mill or lathe and want to make a repair. In this case the cross pin doesn't have to be perfectly centred, and I am aware of situations where it should be centred.

    David
     

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