Chelsea Deck Clock - Broken click pivot screw

Discussion in 'Clock Repair' started by fbicknel, Aug 18, 2019.

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  1. fbicknel

    fbicknel Registered User

    Apr 14, 2017
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    This clock is in pretty good shape, except for the fact that the head was shorn off the click pivot screw somehow.

    Drilling this thing doesn't seem to be in the cards:

    The rig (yeah, I tried the drill press, but the drill bit just didn't want to cooperate.)

    2019-08-18 1406 Screenshot.png
    2019-08-18 1407 Screenshot.png

    But as most of you probably are thinking, that bolt is way too hard for that bit. And I was thinking the same thing, but had to prove it to myself.
    2019-08-18 1408 Screenshot.png
    After several minutes at about 3000 rpm the tidy little detent in the picture above is all I had to prove for my efforts. Nearly as I could tell from the gauge, it was less than .5 mm deep.

    I also am the proud new owner of a flat bit:

    2019-08-18 1408 Screenshot_1.png

    compare to the other end ... which is what it used to look like:

    2019-08-18 1408 Screenshot_2.png

    ANYWAY...

    Ideas for how to get this thing out? the other end of it is shorn off below the brass. There's no gripping it with anything.

    Ideas I've had:
    • Drill and tap a new hole nearby, possibly also moving the click spring around the center of the main wheel arbor as well.
    • Drill through the brass all around the broken screw, ream the resulting mess round again, and press in a bushing, drill/tap that.
    • Find a new plate.
    Regarding solution 2: the OD of the existing hole is about 2mm. Add to that about .75mm for the drill out operation -- X2 -- I'd probably wind up with a 4mm hole after reaming. Fortunately, I do find some 4.5mm OD blank bushings available. The thickness is good (2mm bushing and 2.16mm plate).

    After some consideration, I'm leaning toward the second solution. Seems moving the click might be messy and possibly counter to the design of the clock.

    Anyone like that one? or maybe something else?

    For reference, here's the click, the broken head of the screw and the other end of the screw (arrow):
    2019-08-18 1435 Screenshot.png

    Obviously, everything loose in this picture belongs on the other side of the plate.

    Here's the clock before it was disassembled:
    2019-08-18 1439 Screenshot.png
     
  2. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
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    I don't think
    I would trust a click screw in a pressed in bushing. Try drilling into the screw from the inside. A bit of penetrating applied a couple days before might help. If you have to bush the hole, consider making a bushing with a flange on the inside so there will be no chance of it pulling out. If the screw is hard you may need a carbide grill.

    RC
     
  3. Uhralt

    Uhralt Registered User
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    Sep 4, 2008
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    You can also remove all other steel parts from the plate and use a concentrated alum solution to dissolve the rest of the screw. Search for "alum" on this forum for details how to proceed best.

    Uhralt
     
  4. disciple_dan

    disciple_dan Registered User

    Mar 10, 2016
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    Just as a maybe, take a very sharp scribe and try to manipulate the screw. Either back it out or screw it on thru. Who knows, it might be worth 10 minutes of your time.
     
  5. bangster

    bangster Moderator
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    I wonder why they would use a hardened steel screw for this purpose.

    PS: The alum trick is worth a try.
     
  6. Kevin W.

    Kevin W. Registered User
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    Apr 11, 2002
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    I was thinking alum as well today, i thought it would be worth a try. At least you will still maintain the same hole.
     
  7. Uhralt

    Uhralt Registered User
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    And most importantly the thread will remain undamaged.

    Uhralt
     
    Kevin W. likes this.
  8. Karl Burghart

    Karl Burghart Registered User
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    Alum, works great.
     
    Kevin W. likes this.
  9. fbicknel

    fbicknel Registered User

    Apr 14, 2017
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    Thanks for the great suggestions, all.
     
  10. Jerry Kieffer

    Jerry Kieffer Registered User
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    May 31, 2005
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    You have a number of issues with your procedure.

    First, one should not drill without knowing what is being drilled. Hardness is easily determined in that any metal that cannot be "scored" with a pocket knife is hard.

    Drilling hard metal is generally no issue under the right conditions.

    (1) From the photos it would appear that you are using a carbon steel drill. Neither carbon nor HSS or even some carbide drills are suitable for hard steels. The drill needs to be specifically designed for hard steels. The following link is a quick example. All drilling should be preceded by spot drilling and the use of cutting fluid.
    Armor Drill Tool Machines And Drills Granite, Armorplate, Stone, High Speed Steel, Hardened Steel, Drill Out Broken Taps

    (2) 3000 rpm is far to fast in most cases when drilling. At this speed, you end up doing far more work hardening/cutting tip damage than cutting unless the drill is designed for a specific speed.
    Typically, 1500 rpm is about max for general drilling.

    (3) When drilling, it is important that the drill cannot pull itself into the work piece and overload to the point that it snaps off. One method of doing this, is to only use Leadscrew feed when drilling or something like CNC that offers the same level of control. In this case, the feed is under continuous pressure from the rack and gear carriage hand wheel pressure. Under this condition, the drill is constantly encouraged to instantly take as deep of a cut as is possible at any given moment.

    (4) Your drilling assembly is extended far beyond stability and the ability to control runout. Under these conditions, drills are under far greater risk of breakage. The ideal condition is to have the drill shank mounted in a accurate collet in the spindle nose.

    Personally, I would drill out if the original hole size is to be retained.

    Jerry Kieffer
     

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