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Thread: Metric thread dimensions :-?

  1. #51
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    Putting a thread on a piece of rod, was never so complicated when l was at school

  2. #52
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    Quote Originally Posted by Bigtrev8xl View Post
    Putting a thread on a piece of rod, was never so complicated when l was at school
    LOL... It Isn't

    Start at about the right OD.

    Thread several passes

    when you are close to correct size, try your part, nut, gauge, etc. (You probably need to knock off the burrs first)

    When it fits, you are done. If it does not fit yet, repeat threading passes until it does.

    Wsn't that easy?
    1601

    Keep eye on ball.
    Hashim Khan

  3. #53
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    Like Plunger and others who read all this with a sinking heart. Thread wires? Never used them or seen them used even in a toolroom of 20-30 guys. We had Go/No Go thread gauges for critical stuff, otherwise cut you thread until the nut fits etc.

    I have one 60 degree HSS tool ground for external screw cutting (and another for working up to shoulders) and will cut any metric or unified thread, forget about having the correct end flat for different pitches.

    Given the OP's original post it is obvious he needs to start with basics. If you want to cut an M6 thread, turn the material to 6.0mm and start screw cutting.

    Oh and it sounds like he found the only possible acceptable use for a carbon M7 tap - fixing something unimportant in plastic. In the metric world, M7 is never used.
    Last edited by Peter S; 01-15-2018 at 07:55 PM.

  4. #54
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    How can you have one tool for "any" pitches when the helix angle changes? Sure.. you can get a lot with one, but at some point you need to change angle to hold an accurate thread form.

  5. #55
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    While it is of little use for metric threads, I simply refer to Table V under the Threading tab in the Atlas lathe handbook. It gives depth of feed single depth for a given thread depth either N.F tool or Vee form tool with the compound set at 29*.

    As far as ID threading in a blind hole, I use the same procedure as boring a blind hole. Thread to just before a hard stop and allow a revolution or two before retracting the tool. I feel all the reverse spindle, inside out, upside down dodges just add to the confusion. If you are unable to slow the spindle speed to a rate you are comfortable with, it is a simple matter to make a hand crank for the outboard end of the spindle and turn by hand. I have, on occasion, used an adjustable wrench on the chuck jaw to turn a critical thread to a shoulder.
    Jim H.

  6. #56
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    The word Nominal means (Named) so it is not designed to be accurate so we say 25 mm nominal mm per inch when it is actually 25.4. So nominal is a term we used at university to reflect something (near to, or accepted generally) for talking sake but not exact. Alistair
    Please excuse my typing as I have a form of parkinsons disease

  7. #57
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    Quote Originally Posted by Peter S View Post
    Like Plunger and others who read all this with a sinking heart. Thread wires? Never used them or seen them used even in a toolroom of 20-30 guys. We had Go/No Go thread gauges for critical stuff, otherwise cut you thread until the nut fits etc.

    .....
    Why the "sinking heart"? You used the BEST POSSIBLE test, a gauge. Just a couple gauges may cost more than our lathes. Hardly any of us will have those, WE should have the "sinking heart" when we think about that, we cannot afford such things for all sizes.

    So, lacking the gauges, we use wires if it has to be precise, or check it with the nut if it is just for "general purpose".
    Last edited by J Tiers; Yesterday at 09:50 AM.
    1601

    Keep eye on ball.
    Hashim Khan

  8. #58
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    Quote Originally Posted by J Tiers View Post
    LOL... It Isn't

    Start at about the right OD.

    Thread several passes

    when you are close to correct size, try your part, nut, gauge, etc. (You probably need to knock off the burrs first)

    When it fits, you are done. If it does not fit yet, repeat threading passes until it does.

    Wsn't that easy?
    It should be borne in mind that the internal thread has a rounded trough so continuing to repeat passes will eventually produce a thread that will still not go together but is actually too small. Obviously will never be an issue if the OD is correct.

  9. #59
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    Quote Originally Posted by J Tiers View Post
    Why the "sinking heart"? You used the BEST POSSIBLE test, a gauge. Just a couple gauges may cost more than our lathes. Hardly any of us will have those, WE should have the "sinking heart" when we think about that, we cannot afford such things for all sizes.

    So, lacking the gauges, we use wires if it has to be precise, or check it with the nut if it is just for "general purpose".
    J,
    I shouldn't have mentioned gauges at all. I meant to say I have got by without special gauges or wires and I thought a usually simple job was being made to sound complicated. I thought it might put readers off metric screw cutting, hence my despondent thoughts....I'm over it now

    I do think it is good to understand thread theory e,g, pitch diameter and how to use wires etc.

  10. #60
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    OK. I happen to have a fair number of thread gauges, for common english threads, so it jumped out at me. I've also used wires, and "triangles", which seemed to work very well also.

    But usually the gauge is a nut.....
    1601

    Keep eye on ball.
    Hashim Khan

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