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  1. #1
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    Default Questions on thread measurement

    I've got a need for measurement of exterior threads to class 3 sizes.

    The parts would need to be measured for class 3 limits while still held in a lathe chuck. As I see it, I have three choices:

    1. Thread mic.
    2. Go/no-go ring gages.
    3. Thread wires and a mic.

    The jobs where I have to measure to class 3 spec would be about once every other week, perhaps once/week, and most of the threads I will check will be of two specifications, 1/2-28 and 5/8-24.

    Any opinions which is the best way to go for a job that has to stay in the lathe while being measured? Right now, I'm using thread wires and a vernier mic (down to tenths), and trying to juggle the wires and the mic at the same time gets annoying.

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    The cheap route is...
    Use rubber bands to hold the wires or thread triangles that attach to a micrometer.

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    Your obviously threading suppressor / barrels . Why class three ? Most suppressors/ barrels are 2a.

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    If you are going to use the measurements to inform your next cut, the easiest method is to just get a B & S (or Starrett) 0-1 thread mic with 22-30 pitch (or 22 - 32, some had slightly different ranges). One mic to do both your threads. Depending on the actual requirements for the work, have it calibrated or calibrate it yourself to known standards. Then print out a chart to correlate the readings on the mic to the standard(s) you want to hit.

    A thread mic won't correct for thread form; but if you are confident of that, a mic is easier than go/nogo gage to see where things actually are and how far is left.

    Here's an example, no suggestions about condition

    Vintage Brown and Sharpe Thread Micrometer Mic Mike Machinist Tool | eBay

    In searching for thread mics, i see there are now chinese imports for around $60 with a complete set of interchangeable anvils. Your call, setting one up & qualifying it for the narrow range you expect to work in might still be viable. I like old single range B & S mics for easy convenient use, already set up. Mitutoyo for interchangeable anvils.



    smt

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    Wires work

    Use plasticine to hold them. No need for frustration. Or do the calc on a bent up paper clip. Do it once, and you are done for ever.

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    hold the wires in place with a dab of grease...works every time

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    Quote Originally Posted by akajun View Post
    Your obviously threading suppressor / barrels . Why class three ? Most suppressors/ barrels are 2a.
    That's what several suppressor manufactures are now calling for. Some of the new thread drawings have no alignment shoulder behind the threads, they're depending on the pitch diameter holding the suppressor co-axial to the bore. eg, Thunderbeast is one such manufacture.

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    that just makes no sense to me. The reason that a class 2a is used is to prevent seizure / galling. Why don't they just use an internal thread.
    Granted my thunderbeast is an older model I have had no problems with 2a threads, even when it has come unscrewed during firing.

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    The other replies are correct, but I prefer ring gages. A pair of Go and NoGo ring gages will cost in the neighborhood of $500. I have wires, a thread mike and ring gages. For me, rings gages pay for themselves in time savings. Plus the added benefit of ease of use and greater confidence in gaging accuracy. This is just my opinion.
    Joe

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    Quote Originally Posted by jcoehlo View Post
    The other replies are correct, but I prefer ring gages. A pair of Go and NoGo ring gages will cost in the neighborhood of $500. I have wires, a thread mike and ring gages. For me, rings gages pay for themselves in time savings. Plus the added benefit of ease of use and greater confidence in gaging accuracy. This is just my opinion.
    Joe
    The gages don't exclude the need to measure as you approach the limits, so you still need a measuring method.

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    I hate using wires, and I hate paying for thread gages.

    I've got a couple of Ovee spring gages.. I like 'em. They are basically thread wires in spring form, squeeze them, they
    clip right on to your thread, and then you measure over the spring/wires.. Really quick and easy, no futzing around with
    grease or tape or sponges like with standard wires, clip it on and go.. I think they are a little over $100 each.


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    Quote Originally Posted by akajun View Post
    that just makes no sense to me. The reason that a class 2a is used is to prevent seizure / galling. Why don't they just use an internal thread.
    Granted my thunderbeast is an older model I have had no problems with 2a threads, even when it has come unscrewed during firing.
    That's my opinion as well - IMO, I'd rather have a class 2 thread with a concentric shoulder behind the thread for axial alignment, because, y'know, muzzles tend to be dirtier places on a gun.

    But I'm not making those decisions, and I'm not the SOT selling the suppressors. I'm just the gunsmith/machinist/FFL-01 threading the barrel.

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    Thanks guys, I appreciate your input on this. I'm going to use your suggestions to become better with wires and get a better mic for the job as well. I might get a set of go/no-go ring gages in the future as well. For the work I have on my plate now, I'm going to get better wire technology into my shop.

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    i've all kinds of thread mics and they are very handy, but you still need thread wires (unless you have an anvil for every thread ever made. Grease, Plastercine or silly putty all work as the extra hand....here's another idea i made out of a small piece of inner tube with a couple of slits and a 1/4" punched oil


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    One more thing to make using thread wires easier. Using a non rotating spindle mike. It is the rotating spindle on top that knocks the top wire off. I bought one from a coworker back when Mitutoya mikes were sold out of the back of someones trunk for $15.00 or $25.00. It has an 8mm spindle that makes it easy to catch the bottom wires even if you skip a thread or 2 between the wires. When ever I misplace this mike it is hard to go back to a regular one. In case they still sell these, the model number is 106-102 for a 1 inch mike.

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    I find it easier to put 2 wires on the top of the thread, run your mics to about +.010 of the pitch dia. and slide the third one in the bottom.

    I can't measure threads worth a damn on the bench.

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    The ovee wires are nice and easy to use but are not versatile.

    The best are Marlco thread measuring parallels. You only need one set for each specific thread profile. The best thing about them is that the pitch diameter offset is built into them. Hold the pair hard together and zero your digital caliper or mic on them, then you get a direct pitch diameter measurement of your thread, no calculation required.



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    Mitutoyo has some quite nice (and expensive) three wire units that clip to end of micrometer anvils. I think the product number is 313-101 for full metric set.

    Also Martin + Tschopp has similar units (Guide to 3-wire thread measuring)

    Sent from my D5803 using Tapatalk

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    A good thread mic will pay for itself in the amount of time it takes to fish dropped wires out of the chip pan.

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    Quote Originally Posted by wyop View Post
    I've got a need for measurement of exterior threads to class 3 sizes.

    The parts would need to be measured for class 3 limits while still held in a lathe chuck. As I see it, I have three choices:

    1. Thread mic.
    2. Go/no-go ring gages.
    3. Thread wires and a mic.

    The jobs where I have to measure to class 3 spec would be about once every other week, perhaps once/week, and most of the threads I will check will be of two specifications, 1/2-28 and 5/8-24.

    Any opinions which is the best way to go for a job that has to stay in the lathe while being measured? Right now, I'm using thread wires and a vernier mic (down to tenths), and trying to juggle the wires and the mic at the same time gets annoying.
    You've got the methods right... if your going to be repeating this often, get the thread mic... have a CERTIFIED INSPECTION LAB check the mic and cerrtify it...

    one more thing, to hold the wires on first clean the thread, then use a dab of Vasoline Petroleum Jelly (available at the Drug Store) to hold the wires. and put a sheet of cardboard under all this while you get used to doing it.


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