Thread cutting, making your own sizes?

  1. cocker

    cocker Member

    Messages:
    494
    Location:
    lincs , England
    You will need a tool to cut the external thread and a very similar ( but different ) tool to cut the internal thread . To do this you'll need to either grind them your self or buy expensive tooling .
    Ooorrr get a tap and die in the nearest size you want . Don't forget to look at all the imperial sizes - something will be close .
     
  2. earthman Member

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    1,401
    I bought a set of lathe tools some time ago, that has the internal and external thread holders/tips.
     
  3. Hood

    Hood If it walks like a duck....

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    Location:
    Carnoustie, Scotland
    Chances are the inserts will just be partial profile rather than full profile. That will mean that they are capable of cutting various pitches but they will not produce the correct root or crest.
    As mentioned before that is not really a concern for what you are wanting to do as you are doing a one off thread and doing both the male/female parts of it so you can make it to suit.
     
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  4. earthman Member

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    1,401
    lathetool.jpg

    I've just had a closer look at what is suppose to be the internal threading tool holder in my kit,.....maybe someone can correct me if I'm wrong but surely that cutting tip is wrong for that operation??
     
  5. Spark plug

    Spark plug Member

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    3,663
    Location:
    Durham, England
    That looks to be an external insert in a internal holder.
     
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  6. Hood

    Hood If it walks like a duck....

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    11,804
    Location:
    Carnoustie, Scotland
    Aye, as above, external insert in the internal holder.
     
  7. earthman Member

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    1,401
    Thanks chaps,...can anyone post a picture/link of what the correct insert should like then?
     
  8. Hood

    Hood If it walks like a duck....

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    11,804
    Location:
    Carnoustie, Scotland
    External Right hand

    ScreenHunter_3399 Dec. 10 20.28.jpg


    Internal Right Hand

    ScreenHunter_3400 Dec. 10 20.29.jpg
     
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  9. Hood

    Hood If it walks like a duck....

    Messages:
    11,804
    Location:
    Carnoustie, Scotland
    BTW for left hand tools they would look the opposite, so the top would be what an internal left hand would look like and the bottom an external left hand.

    Your tool however is right hand so go with the post with the picture :)
     
  10. Spark plug

    Spark plug Member

    Messages:
    3,663
    Location:
    Durham, England
    This is what the internal tool /insert should look like:

    upload_2019-12-10_20-32-7.jpeg
     
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  11. RichardM Member

  12. Pete.

    Pete. Member

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    9,472
    Location:
    Kent, UK
    Make it easy on yourself. Take a piece of silver steel about 1/2" diameter and turn a length of the shank down to 10mm leaving the very end at 1/2". Now turn a 60 degree vee in the end and grind it down one side to the centre line. Harden it and you have a tool that will cut both internal and external threads.

    threading tool.jpg
     
  13. Screwdriver

    Screwdriver Member

    Messages:
    6,476
    UK London
    Nice tip.

    If I was going to "make one up" I'd still probably pick the nearest standard and aim at that (though not necessarily aim for it). I'd do the internal first then just keep cutting the external thread until it fits.
     
  14. Dr.Al

    Dr.Al Forum Supporter

    Messages:
    682
    Location:
    Gloucestershire, UK
    If you're ever find yourself needing to screw-cut a small thread of a relatively standard pitch (e.g. 1 mm), or even a bigger one of something like 1.5 mm pitch, one option is to buy a pair of HSS taps of the right pitch (i.e. M6 for 1 mm or M10 for 1.5 mm). Get one for a normal right-hand thread and one for a left-hand thread (i.e. anticlockwise to tighten). Then grind off all but one tooth on one of the flutes. The left-hand thread tap can then be used either as an outside full-pitch single-point threading tool or (if your lathe has a suitable chuck mount) as an internal threading tool with the lathe running backwards. The right-hand one can be used as an inside tool or an outside one with the lathe running backwards. Running the lathe backwards makes for a much easier threading experience.

    Taps are cheap and if you break the tip, you can rotate it to offer up the next flute and carry on using it. You can use things like M10 fine or M10 extra fine to get a more robust tool with different pitches (1.25 mm and 1 mm in these cases), but the taps tend to be a bit more expensive than coarse pitch taps.

    The only major disadvantage is they don't tend to be very long, so you can't use this if you need to cut a thread fairly deep in the body. At a push I've used this once to cut an internal thread without grinding the extra teeth off; the disadvantage of this is you have to coordinate your hand movement a lot more and wind the cross-slide until the tap disengages before you disengage the half-nuts.
     
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  15. earthman Member

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    You 'hit the nail on the head' there, I've just checked the other holder, inserts had just been switched.:doh:
     
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  16. 123hotchef Member

    Messages:
    9,658
    Location:
    Kent
    I am in the same boat not had the balls to try screw cutting inside or outside yet just use taps and dies
     
  17. earthman Member

    Messages:
    1,401
    Great tip that, just need some fine grinding skills I guess,.....not sure I have, I've shy'd away from shaping the tiny HSS lathe tools I have.:whistle:
     
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  18. earthman Member

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    1,401
    There's a first time for everything hey.:)
     
  19. Screwdriver

    Screwdriver Member

    Messages:
    6,476
    UK London
    I struggled for a long time before I discovered my Colchester had an idler gear in place of the correct thread cutting gear. All my threads up to that point had been almost exactly wrong.
     
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  20. 123hotchef Member

    Messages:
    9,658
    Location:
    Kent
    u tried yet?
     
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