Three Wire Thread Measurement
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    Default Three Wire Thread Measurement

    Hi: I am very interested to learn the correct way to measure 60 degree threads using the three wire system. My first question is concerning the quality of thread wires; who makes the highest quality wire? My second question is the correct formula for calculating MOW Max./Min. Any input on this subject would be greatly appreciated.

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    Here is a link.
    http://www.threadcheck.com/html/3wir...FRJdxwodXSv7xg
    Not only is the size of the wire critical, but the measuring tool and proceedure as well. You need to be adept at using mirometers. Tough for a novice. RJT

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    I bought some thread measuring wires from Van Keuren. I had a bigger acme thread that was left hand and double start. Don't know if there the best wires, but they had excellent customer service. I called a few times and got a bunch of information, they even figured out the math for me with their computer program.

    www.vankeuren.com

    http://www.vankeuren.com/tmo.aspx

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    van Keuren makes the best ones I've found.

    My set has about 40 different thread pitches, and the wires are spec'd to 10 microinch resolution.

    For example, the 20-pitch wires are 0.02887" diameter. The pitch diameter is given as the measurement over the wires minus 0.04331".

    Of course this assumes that you have the ability to make the measurement with 10 microinch accuracy.

    There are some bench micrometers with this resolution, but they're quite large, not hand-held units. This style is quite a bit easier to use than the smaller ones when doing thread measurements.

    - Leigh

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    Default Three Wire Thread Measurement

    Thank you for the information. The sources you have supplied will be very valuable. I appreciate it!

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    Also check out Michael Rainey's "ME ThreadPal" here:

    http://closetolerancesoftware.com/METhreadPal.html

    It calculates the most obscure thread criteria, including best wire size and measurement tolerances.

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    Also check out Michael Rainey's "ME ThreadPal" here:

    New version out - described here:

    http://www.practicalmachinist.com/vb...02#post1039002

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    Default 3 wire trick

    Here is a trick I came up with for using 3 wires. I tape the 2 bottom wires together with a small gap between them. It makes it a lot easier to hold it all together. Also I always lay a rag or piece of paper over the lathe bed when I do it, its much better than picking through a big pile of chips looking for a little wire. JC

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    I've seen a couple of pieces of wide rubber band material used to hold the wires - keeps all three together as a unit and out of the chip pan, plus the elastic pulls the wires against the thread flanks while you measure.

    Truly a crap sketch, but you can see the idea.


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    I found a small piece or plado or any kind of puddy type material will do. Stick the wires in the puddy on one side that will free up a hand to measure. Same thing as the tape idea.

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    If the part is big or hard to hold the wires and mic at the same time I just stick the 2 wires to the part with a little dab of grease, works great.

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    Quote Originally Posted by Cuda View Post
    If the part is big or hard to hold the wires and mic at the same time I just stick the 2 wires to the part with a little dab of grease, works great.
    A+ on the grease, works everytime.

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    The wire holders that have a hole in the base that slip-fits on the mic anvil are the schizzle!
    The Etalon indicating mic that has the push button anvil retraction feature is also the schizzle for three-wire work! The fact it can be easily converted for use with a probe and amplifier to get you down to 0.0000001" is also kinda groovy!

    Look Ma... just two hands!

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    Google PEE DEE THREAD MEASURING WIRE SET, They come in a complete set with a chart for all the calculations explained. Very reasonable.

    Lord Byron

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    It's true, the 3-wire thread system is difficult to manipulate with a micrometer, but being a good machinist is developing skills to overcome this difficulty. I used to teach my students to do this manually by holding the wires in one hand, and the micrometer in the other while the workpiece was held between centers.

    The charts in the PEE DEE set give you the reading over the wires equivalent to the maximum allowed pitch diameter; you can get the minimum allowed pitch diameter for any class of fit from the Machinerys Handbook. The difference between the maximum and minimum is the tolerance. There is no hocus-pocus about it.

    If that doesn't fit your definition for a "precision screw thread", what does?

    It's true, a thread plug gage does seem the only option for measuring internal threads. Machining a thread plug gage is a very real possibility if the part that you are threading internally has critical dimensions, or if you have a lot of them to do. I have seen a low melting point metal that can be used to pour in the internal thread, then screw the plug out and measure it with thread wires, or a thread micrometer. I don't know the name of the metal, or where to obtain it. I have never had any experience with it.

    Don't get me started on threading, I could blander on and on.


    Lord Byron

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    Silly putty helps me.

    img_20160403_154427_1.jpgimg_20160403_154458_1.jpgimg_20160403_154510_1.jpg

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    Quote Originally Posted by complete loser View Post
    Silly putty helps me.

    img_20160403_154427_1.jpgimg_20160403_154458_1.jpgimg_20160403_154510_1.jpg
    That is a pretty good idea. Measuring over wires has always been kinda a bitch. What do you do it the thread is 4 or 6 inch in diameter? Grease is what I do.

    Didn't read the whole thread...


    Brent

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    I have mostly Van Kueren wires. They are inspection quality. I also have a couple sets from SPI that include holders that snap over the mike anvils. SPI also gave the constant you subtracted from the mike reading to get pd. Don't know if SPI still offers them.

    If you are measuring work in the lathe put a towel over the ways. Finding a small wire in the chip pan is no fun.

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