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Thread: Rethreading screws (the search for replacement screws)

  1. #1
    Between here and there
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    Replacement screw for Sinar Norma

    I am in a pinch ...

    I think I need to replace a shoulder screw. It all looked like the sunny side of the street, that it would be a regular M5 screw. A slotted screw, but still ... no problem. Off to the local store, bought a box.

    At home I tried it, and well ... no luck. Remeasured, still looks like it should be M5.

    Waffling around on the internet, I happened to see references to M5 having a finer pitch (0.75 mm) earlier on (pre-1970). Short of trying to build a time-machine and go back in time ... what are the options?

    Can one rethread a standard M5 screw? Would a machinist be able to make a bunch of replacement screws from an original one?

    EDIT:

    I am adding a photo of the screw, this should be in the swing mechanism of a Sinar Norma. I measure it as 17 mm long, with a diameter of 5,19 mm.

    Click image for larger version. 

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    Last edited by Jimi; 16-Sep-2020 at 12:52.
    "Be still and allow the mud to settle."

  2. #2
    Tin Can's Avatar
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    Re: Rethreading screws (the search for replacement screws)

    Seems McMaster Carr has special 5mm screws that don't fit normal pitch

    "Fine-Thread Metric 316 Stainless Steel Button Head Hex Drive Screws

    Closely spaced threads on these screws fit in holes with a fine pitch. They're not compatible with standard metric threads. Made from 316 stainless steel, they are more corrosion resistant to chemicals and salt water than 18-8 stainless steel screws. Screws may be mildly magnetic. Length is measured from under the head.

    3D CAD models availableFor technical drawings and 3-D models, click on a part number.

    Lg.,
    mm Threading Head
    Dia., mm Head
    Ht., mm Drive
    Size, mm Tensile
    Strength, psi Each
    316 Stainless Steel
    M5 0.5 mm
    10 Fully Threaded 9.50 2.75 3 80,000 90943A117 $4.45
    12 Fully Threaded 9.50 2.75 3 80,000 90943A118 4.96
    16 Fully Threaded 9.50 2.75 3 80,000 90943A119 5.50"
    where is the monolith

  3. #3

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    Re: Rethreading screws (the search for replacement screws)

    A machinist should be able to cut threads of any kind either with single point threading or with a thread cutting die after turning a blank.
    How badly mangled is the screw ? if the screw is damaged there may damage to the threads in the screw hole.

  4. #4
    Between here and there
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    Re: Rethreading screws (the search for replacement screws)

    Thanks Tin Can and Jim,

    good to know where to start at least, and that it might be possible to get out of the bad situation. The screw is partly mangled - I guess it was galling. There was a large amount of lubrication residue, and traces of some dry, white powder. I may need to soak the parts and clean it out much better next time. The threads of the steel part are fine, as far as I can see, and I am able to thread a clean screw all the way through, with no obvious resistance.

    A good few lessons learnt.
    "Be still and allow the mud to settle."

  5. #5
    Tin Can's Avatar
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    Re: Rethreading screws (the search for replacement screws)

    I always try my Thread Files on damaged screws first

    Even if the thread and file mismatch, I use the closest possible

    For small screws put file on bench or in vise and rub screw over the cutting edges

    Here is one that has 0.75 mm pitch, I have at least 4 thread files, each with 8 different pitch

    https://www.amazon.com/General-Tools.../dp/B0017R1DOM
    where is the monolith

  6. #6

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    Re: Rethreading screws (the search for replacement screws)

    are you sure its metric? a 10-32 is very close to that size.

  7. #7

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    Re: Rethreading screws (the search for replacement screws)

    What is the screw off?
    This might help id the thread [ie whitworth, BA, unified, or metric]
    The pitches of the various thread forms are:
    Whitworth 1/4 - 20 - 0.0500 inch
    1/4 - 26 - 0.03846 inch
    Unified #10-24 - 0.04167 inch
    #10-32 - 0.03125 inch
    Metric 6mm 1mm OR 0.75mm
    BA 0BA 0.03937 inch


    Regards
    Tony
    Last edited by tonyowen; 14-Sep-2020 at 07:56. Reason: incomplete

  8. #8

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    Re: Rethreading screws (the search for replacement screws)

    [QUOTE=Jimi;156821M5 having a finer pitch (0.75 mm) earlier on (pre-1970).?[/QUOTE]

    Assuming it is 5mm x 0.75 pitch then machine screws of this size are available from Amazon and others

    regards
    Tony

  9. #9
    Drew Wiley
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    Re: Rethreading screws (the search for replacement screws)

    Metric pitch standards never changed, but in certain diameters there are both standard and finer thread options. Then you've got the oddballs like Whitworth, "British metric", or custom wholly nonstandard. I've never encountered a use for the strange ones except on certain Brit cars. Ironically, willy-nilly wholly nonstandard screws are more apt to be current Chinese or Indian junk screws, as are many of the hardware screws screws on the market now which are improperly made. Here in the US, I'd try McMaster first since they have actual specs for each item and are straight shooters. I have no idea about EU sources. Really specialized dealers without an internet profile are going to be tricky at the moment due to the virus issue. Normally, there's a superb nut n' bolt house here; but they aren't even open at the moment.

  10. #10
    Between here and there
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    Re: Rethreading screws (the search for replacement screws)

    Thanks for your answers - I have been assuming that it has metric threads, but assumptions only go so far ...

    I bought some tools to get a more exact measure, since a loupe and a ruler is too rudimentary in this case. I am going to see if I can make a photo of the screw too, just to show the damage.
    "Be still and allow the mud to settle."

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