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what kind of thread is 1/2 - 12 tpi

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  • what kind of thread is 1/2 - 12 tpi

    Somehow the nut holding the wheel on my bench grinder got welded to the shaft and I had to cut the nut off. Now I have to buy a new nut and probably get a rethreading die to fix the boogered threads.

    The major dia. of the thread on the shaft mics at .493. But, it's not a 1/2 - 13 thread. The threads are 12 tpi. Obviously not a UNC thread form.

    Any idea what kind of threads these could be? This one is on the right hand end of the shaft so they are right hand threads.

  • #2
    Could it be a Metric thread??

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    • #3
      1/2" x 12 is British Standard Whitworth.
      The first standardised thread in the world and produced years before the abortive 1/2" x 13 UNC came out.

      Many American lathes can't even screwcut 13 tpi.
      .

      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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      • #4
        From the size you mention it could be 1/2" BSW.

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        • #5
          It's a 1/2" -12. You might be able to press the shaft out of the armature and replace it with whatever you want. Or thread a new nut on a lathe.

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          • #6
            1/2-12 used to be a fairly common thread in the US, but it was many years ago. I've seen old tap & die sets that contained that thread. The antique planer at Buckley has some threaded parts that are 1/2-12 also. I'd bet that you can buy both taps and dies for 1/2-12 today.

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            • #7
              Originally posted by John Stevenson
              1/2" x 12 is British Standard Whitworth.
              The first standardised thread in the world and produced years before the abortive 1/2" x 13 UNC came out.
              And is still used in printing equipment

              Originally posted by John Stevenson
              Many American lathes can't even screwcut 13 tpi.
              Hum, have never seen an American made lathe that could not cut 13 TPI.

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              • #8
                Well this is a chinese bench grinder that looks just like all the other chinese bench grinders you can find with 25 different labels on them. It can't be more than 10 years old.

                I'm positive it is 12 tpi. I have a thread pitch gauge that fits it perfectly.

                So, anyone know where I can buy a 1/2 - 12 BSW nut?

                It would be nice to be able to turn my own but, sadly, I don't own a lathe.

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                • #9
                  Triskidecaphobia

                  John is right.

                  The original imperial/inch thread: 1/2"-13-BSW.

                  They are still in good supply here in OZ - BSW, BSF, SAE, UNC, UNF and metric (of course) etc.

                  I liked the story that John Stevenson told here that the Chinese being the superstitious lot that they are and who regard 13 as bad luck only use 12tpi.

                  It seems that the crafty buggers passed it onto the Yanks.

                  I suspect that the USA being what it is used a 12tpi as it is easily cut with a thread-cutting dial on a standard 2, 4, 6, 8 tpi lead-screw. It also made it much easier for gear trains and quick-change gear-boxes.

                  13tpi had a lead of 1/13" = 0.0769" x 25.4 = 1.954mm so cutting a 2mm thread will or may do the job, but if it is in fact a whitworth thread you will need a 55* thread form and not the normal 60* form.

                  Short and easy answer - get John S to post you one from the UK. He always seems only too willing to help his 'merican cuzzins.

                  And one for the "come in handy later" file - and to use Wikipedia - as regards fear of 13:
                  http://en.wikipedia.org/wiki/Triskidecaphobia

                  I've waited years to use it!!!!

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                  • #10
                    Originally posted by John Stevenson
                    1/2" x 12 is British Standard Whitworth.
                    The first standardised thread in the world and produced years before the abortive 1/2" x 13 UNC came out.
                    True, but the first is rarely the best, that's why UNC and Metric have 60 Deg threadform.

                    Measure the threadform angle, if it is 55 then it's Whitworth, if it's 60 then your machining a new nut and/or a spindle, or just go out and buy a new grinder.
                    The shortest distance between two points is a circle of infinite diameter.

                    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                    Southwestern Ontario. Canada

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                    • #11
                      By the way, Victor Machinery sells 1/2-12 taps and dies. (Plus more special thread taps and dies than you could imagine).

                      http://www.victornet.com

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                      • #12
                        Originally posted by John Stevenson
                        1/2" x 12 is British Standard Whitworth.
                        The first standardised thread in the world and produced years before the abortive 1/2" x 13 UNC came out.

                        Many American lathes can't even screwcut 13 tpi.
                        Abortive? you're referring to Whitworth threads there, of course - so you may want to rearrange your adjectives a bit, sir.

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                        • #13
                          find someone with a triumph or bsa. motorcycle and steal one from the bike.

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                          • #14
                            If only you knew someone who was a machinist who could make you one....
                            Location: Saskatoon, Saskatchewan, Canada

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                            • #15
                              I think I may have a couple laying around, I will look tommorow, actualy later today.

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