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3 wire thread measuring

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  • lazlo
    replied
    Originally posted by oldtiffie
    Frankly, I'd opt for a thread micrometer with a set of changeable anvils if the job was that important and there was no other alternative.
    I bought a thread micrometer from CDCO for $50. Works great -- way quicker than thread wires. It's limited to 0 - 1", so in the rare cases where I'm doing threads bigger than that, I use thread wires.

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  • oldtiffie
    replied
    3-wire measurement

    There might be a re-think needed here.

    If I had the need for a 3-wire set (I've got one), I'd look for other options first - such a nut with a hole tapped with a good HSS tap. I'd make nuts and cut a radial slot (hack-saw) through one side and about half-way through the other (sort of like a common button die) on two of them and leave the other/third "as is". I'd spread those nuts with a screw-driver/wedge in the slot so that I had three nuts to be used progressively as regards "fit" as I was working my way through the thread cutting in this order:
    - "like a dick in a shirt-sleeve" (loosest fit);
    - "getting close"; and
    - "that's it".

    Using the 3-wire method, keeping the 3 wires under control is not all that is needed. Measuring accurately to the order of accuracy suggested by the need for the 3-wire method is pretty well an art in itself.

    The number of points that must remain in contact simultaneously is very large.

    Each of the three wires will have three simultaneous points of contact: the two flanks of the thread and the face of either the spindle or anvil of the micrometer.

    The micrometer axis must not only be normal to the thread axis but pass through it while keeping all 3 wires in place.

    The order of accuracy is to be better than 0.001" and usually much better.

    Use of the 3-wire method pre-supposes and requires a thread form (and tool) that is very accurate indeed - which is or may be very difficult in a HSM environment.

    I'd practice pretty extensively first on a known good (read: precision ground) thread first to get consistent good measurements as there is quite some practice and skill needed.

    There is quite a market for tools/"gadgets"? to hold the 3 wires.

    Frankly, I'd opt for a thread micrometer with a set of changeable anvils if the job was that important and there was no other alternative.

    http://www.machineryhouse.com.au/Pro...stockCode=Q138

    http://www.google.com.au/search?hl=e...e+Search&meta=

    The "3-wire method" has been "talked-up" as a sort of highly necessary/essential skill that is absolutely needed as a "right of passage" and a "holy grail" for someone to be called a "Machinist". I have three responses to that:
    - maybe so;
    - maybe no; and
    - BS.

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  • lazlo
    replied
    Cool -- thanks McRuff!

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  • Mcruff
    replied
    To check the cavity for texture, appearance, engraving and such, if it shows up in silly putty it will show up in the plastic part. Silly putty is basically silicone based. Silicone flashes in a mold at around .0002-.0003 air gap.

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  • lazlo
    replied
    What do mold makers use Silly Putty for?

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  • Mcruff
    replied
    I use modeling clay or Silly putty. Being a mold maker Silly putty is standard fair and in all moldmakers boxes anyway.

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  • lazlo
    replied
    Originally posted by torchroadster
    With all due respect I've read this forum several times a day for the past 18 months and don't recall seeing this one before.
    Holding thread wires w/only 2 hands

    Thread Wires...

    Originally posted by lazlo
    Holding thread wires w/only 2 hands

    In that thread we talked about grease, scotch tape, silly putty, sticky tack, and my favorite -- sticking the ends of the wires in the black electrostatic foam that chips are shipped in.

    But Airhead's post #15 is a classic:

    http://bbs.homeshopmachinist.net/sho...2&postcount=15

    Leave a comment:


  • torchroadster
    replied
    Originally posted by lazlo
    We really need a sticky FAQ. This question comes up every couple of weeks. Same as "how to center square stock", ...
    With all due respect I've read this forum several times a day for the past 18 months and don't recall seeing this one before. Not that it shouldn't being a sticky - especially with the search feature not working well right now.

    Thanks for all the ideas guys - I can't wait to try them out!

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  • lazlo
    replied
    We really need a sticky FAQ. This question comes up every couple of weeks. Same as "how to center square stock", ...

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  • juergenwt
    Guest replied
    Just put a little grease on the thread top and bottom or all around if you want. Put the wires in the thread and measure bringing your mike up against the bottom wire first. Just like bobw53 said. The small amount of grease will not effect your measurement.

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  • kvom
    replied
    My machining textbook shows the wires being held with rubber bands.

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  • hornluv
    replied
    I had to do this not too long ago and I used a chunk of green floral foam from the craft department at Walmart. It's made to have stuff stuck into it. Works great and really cheap.

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  • SGW
    replied
    Re: clay. You wouldn't put it on the threads; you'd stick the 3 wires into it, like with lazlo's foam idea (which sounds handier than modeling clay....)

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  • lazlo
    replied
    Get a small piece of soft foam, like the black electrostatic foam that chips are shipped in. Poke two of the thread wires into the foam along the bottom, and snug it up under the thread. The poke the remaining thread wire into the foam over the top, and use the micrometer jaws to clamp the three wires, held by the foam, together.

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  • torchroadster
    replied
    I guess the thickness of the grease, clay, etc. in the root doesn't affect the measurement much?

    Forrest: I understand your tape method - I'll give it a try!
    Last edited by torchroadster; 06-13-2008, 10:15 AM.

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