A First (for me) Double screw shear - Optimus 930

Discussion in 'Fettling Forum' started by Alex Smith, Jul 13, 2020.

  1. Alex Smith

    Alex Smith United Kingdom Subscriber

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    Stripping down a Optimus 930. The screw that secures the frame to the fount was proving difficult to loosen (a particularly abused 930) . Soaked in penetrating oil for a couple of days, still no movement. Heated it up, cooled it, then applied screw driver and attempted to undo. I managed to shear the head of the screw off.

    Removed frame, and attempted to remove the stub of the screw from the fount using pliers. The screw then sheared a second time leaving the stub in the top of the fount. Frustrating.

    First time I have seen it, a double shear on on a screw.

    130720 Sheared bolt Optimus 930.JPG
     
  2. podbros

    podbros United Kingdom Subscriber

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    I feel your pain there, Alex.. : (

    Is the Hexagon head soldered to the fount?...Could it be un-soldered at all?

    Best of luck with it
     
  3. Alex Smith

    Alex Smith United Kingdom Subscriber

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    @podbros not sure, I'll need to have another look at it. Wondering if I can drill the remains of the screw out at the moment.
     
  4. podbros

    podbros United Kingdom Subscriber

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    Always tricky when it's a steel screw, and presumably the threaded 'hex' is Brass?

    Drilling bigger then re-threading with a larger thread is the easiest way?

    If you are going that route i would drill a small hole first to act as a pilot?
     
  5. Alex Smith

    Alex Smith United Kingdom Subscriber

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    That might be the solution. I'll give it some thought before commencing work. Thanks.
     
  6. MYN

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    Its not common for a steel screw to get seized in threaded brass unless someone used some high strength threadlocking compound on it. It would be unlikely for anyone to solder it with the screw holding the frame and plate together, I guess.
    Now that it's broken off, perhaps you might try to heat and de-solder the hex nut from the fount so that it could be clamped in a proper vice or something for drilling out and removal of the remaining screw section. Or even replace it with another brass nut if you could find one.
    Just a suggestion because there's a risk of damaging or distorting the fount when you attempt to drill out a really seized screw directly.
     
  7. ROBBO55

    ROBBO55 Subscriber

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    @Alex Smith

    Bugger!

    I had something similar recently but it was brass in brass. The hardest part is to drill the centre of the broken stud.
    I made a guide that fitted snugly into the threads with a 2mm (5/64") hole in the centre.
    (You need to know if you are drilling into a blind hole or not) :-k

    P7080064.JPG

    Then enlarged the hole a little at a time up to the size of the required taping drill size.

    P7080065.JPG P7080066.JPG

    Used a plug tap (bottom tap) to remove the old screw threads and clean the thread in the nut.

    P7080067.JPG
     
  8. Nils Stephenson

    Nils Stephenson Founder Member

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    I'm not sure, but I believe that nut is crimped into the tank as well as soldered. As there is a bit of a recess at the top of the nut, using the method Martin suggested should work. From memory it is a normal M4 thread. It is a blind nut, so don't drill too deep.
     
  9. MYN

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    I forgot that there might be catch inside the fount similar to a Petromax. The nut might not fall out even if unsoldered.
    Then it leaves you no choice but to drill/tap out the broken screw on the fount itself.
    I'll add that Martin's a professional. His 'touch' on things mechanicall would be way different from many of us here. I'll reckon that these problems wouldn't trouble him as much as they would for most of us.:)
    If you have a machine shop or mechanical workshop operating around, it might be a lot easier and convenient to do it on a milling stand where the drill bit could be kept straight with a controlled downward force. They'll have a way to clamp the fount in place to prevent any unwanted movements. They're much steadier than the usual stand-drill as well. Its less likely to slip or break off this way. Note that its much harder to drill out a steel bolt compared to a brass one. You'll need extremely steady hands if you're doing it with a hand drill and some speed control as well. Those guys in the workshop are usually quite adept in the removal of broken bolts and studs. They might do you a favour. Otherwise, you'll have to DIY with some risks involved.
     
  10. Alex Smith

    Alex Smith United Kingdom Subscriber

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    Gentlemen, thank you for helping me out, your sage advice is very much appreciated. For the time being it may get parked in a box and I'll come back to it later. I need a decent workshop and some thought before I tackle this one.
     
  11. JonD

    JonD Subscriber

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    Is this a case for using an Easy-out maybe?

    They have left handed threads so if you drill the remains to the correct diameter you might get one to engage the core which is left behind and unscrew it.
    It's true that in the crown of a fount you don't have much depth to work with so go very carefully and best of luck.

    If it does not go well there is brazing or soldering to fix it. Better that than a tank with a parting bottom disc!
     
  12. bp4willi

    bp4willi Germany Subscriber

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    If nothing else works, saw off the nut.
    Replace with one, soldered in place.
     
  13. podbros

    podbros United Kingdom Subscriber

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    Easy-outs are fine when the stud is bigger and not so seized?...Hum..M4..i don't know :-k

    ...you don't want to shear one of those off in there as well? ](*,)...;)
     

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