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  1. #1
    Join Date
    Mar 2009
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    Brisbane
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    Default How To Avoid Cross Threading Bolts and Screws

    I was helping someone fix some rattles on his motorhome the other day, and he had to remove a seat belt fitting to get access. On re-assembly, he cross threaded the associated (fine thread) bolt just a little, and luckily recovered without drama.
    This can be a tricky area to repair.

    I reminded him of an hint from my old workshop machinist leading hand in the Brisbane City Council Workshop in Mayne Brisbane (where at the elderly age of fifteen I learned the basics of lathes, bandsaws, drilling machines, arc welding, and how to make "air brake switches" for 110Kv).

    He said that when inserting a bolt or machine screw into a threaded hole by hand, line up the angles, and then always turn it firstly in reverse rotation gently until you feel it "skip over" the thread start point, then tighten in the normal direction.

    After a while, you do it instinctively.

    Works in most situations, and is especially useful for larger fine threads and valuable machine tool attachments.
    Also handy for self tappers and wood screws etc where you don't want to start a new thread.

    Try it also on those situations where there is an interference fit on "one-time-use" bolts, which is possibly a worst case scenario.

    I thought twice about submitting this, as it it such a small hint.
    Anyway ...

    cheerio, mike

  2. #2
    Join Date
    Aug 2004
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    Sunbury, Victoria, Au.
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    Default

    Thanks for that Mike! A handy tip
    Russell (aka Mulgabill)
    "It is as it is"

  3. #3
    Join Date
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    Townsville
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    Default

    When I was in my trade I also did this when screwing the spraygun nozzle back on. I've seen quiet a few people strip the thread on the gun while trying to get the nozzle back on.

    Simo

  4. #4
    Dave J Guest

    Default

    I think it's a good tip.
    It was only a few weeks ago I was having my 13 year old grandson help me with some M5 bolts and taught him to do it the same way as he was having problems. Once he did it he no longer had any problems.

    Dave

  5. #5
    Join Date
    Jul 2010
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    Melbourne
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    Default

    Works when replacing self-tapers also, so you dont cut a second "thread".

    Stuart

  6. #6
    FenceFurniture's Avatar
    FenceFurniture is offline The prize lies beneath - hidden in full view
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    Default

    Mike, it matters not that it may be a small hint, and it's definitely worth posting. For myself I was taught this trick by my Tech Drawing teacher, and he went on to say that you can also count the number of parallel threads by the number of clicks you get in one backwards revolution of the nut (such as in starter motors where the threads are very steep for speed and need multiple threads for strength). I think at the time we were doing a drawing of a starter motor.
    Regards, FenceFurniture

  7. #7
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    Ballina N.S.W.
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    Default

    Mike48,
    That is a good tip, I use it all the time especially on very fine threads made out of aluminium like you find on binoculars,camera's etc. For long bolts threaded rods etc I find if you place the bolt at around 60 degrees to the hole and as you rotate the bolt increase the angle to 90 degrees. This helps in picking up the lead thread, works real well when screwing in to round bar.
    Bob

  8. #8
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    Mar 2009
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    Brisbane
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    Default

    Quote Originally Posted by krisfarm View Post
    Mike48,
    That is a good tip, I use it all the time especially on very fine threads made out of aluminium like you find on binoculars,camera's etc. For long bolts threaded rods etc I find if you place the bolt at around 60 degrees to the hole and as you rotate the bolt increase the angle to 90 degrees. This helps in picking up the lead thread, works real well when screwing in to round bar.
    Bob
    Hi Bob
    Hmmm ... must try that out; sounds good.

    You know I think a lot of technically minded people must carry out the "reverse start" instinctively at times, without even thinking about it, especially on things like cameras with those 40mm (inter alia) threads.
    And even on those 100mm PVC SWV waste screw caps etc.

    I used the technique all the time when I moved into Aviation Radio Engineering, where RF connectors of all types used fine threads (eg 5/8 24tpi UNEF) which is large relative to the size of the device.
    If you cross threaded the things, it was sometimes very difficult and time costly to correct the problem.

    My earlier quote with the seat belt anchor point situation has legal implications (I believe that any "official" repair has to be equivalent to OEM spec, not just a cleanout with a tap), not to mention the lost sleep that one might get when remembering a damaged thread, and the possibility of a subsequent accident.
    I cringed when I saw he had cross threaded it.

    I have actually been in a car accident where the car (Morris Mini) hit a rock wall in a road cutting at about 60 deg, and at about 60 Kph, and the impact pulled the front seat belt anchor out of the floor. Luckily the driver survived unharmed, except for some seat belt bruising and a few welts. I was in the back seat, belted up and unharmed, though quite bruised and shaken.
    Last para added as an edit - old age memory loss!

    mike

  9. #9
    Join Date
    Oct 2009
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    Springfield NSW
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    Default

    great tip.

    After reading this I realised that I do this by instinct. I don't know where, when ,how or why I started doing it.

    Now I at least know why.

    Thanks again.
    ____________________________________________________________
    there are only 10 types of people in the world. Those that understand binary arithmetic and those that don't.

  10. #10
    Join Date
    Aug 2011
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    Thats a good tip. It's a tip I have not heard since my old man (fitter and turner) said the same thing to me many years ago. It's funny how your parents tell you stuff and at the time it's in one ear and out the other, but it gets recalled many years later when you have the maturity to appreciate it.

    I too do this almost instinctively with most threads.

    Simon

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