Tolerance on threading inserts? How close can you get by measuring top of thread?
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    Default Tolerance on threading inserts? How close can you get by measuring top of thread?

    I got a repeat job here with a 1.75 - 16 TPI external thread in aluminum. I always check the thread with gages when setting up and then use mics on top of threads to keep an eye out for changes. Seems like I always get the same measurement on top when gage is good. Tempting to just specify an OD range in my notes and go with that. Hate the feel of gages on gummy aluminum.

    Just wondering what kind of tolerance I can expect from the threading inserts (sandvik 266)? How close can I get by just measuring crest of threads? Anybody else do this or is it terrible idea?

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    Quote Originally Posted by mmurray70 View Post
    I got a repeat job here with a 1.75 - 16 TPI external thread in aluminum. I always check the thread with gages when setting up and then use mics on top of threads to keep an eye out for changes. Seems like I always get the same measurement on top when gage is good. Tempting to just specify an OD range in my notes and go with that. Hate the feel of gages on gummy aluminum.

    Just wondering what kind of tolerance I can expect from the threading inserts (sandvik 266)? How close can I get by just measuring crest of threads? Anybody else do this or is it terrible idea?
    If they are Sandvik they will be very repeatable in my experience.
    You should always check though, it is part of the job.

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    Seems like tempting fate.
    Sandvick good and great but a crest check?
    Inside one box our more of inserts this may and should work very well with one date code.
    Bob

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    Playing with fire. Sandvik makes a new batch, maybe .0003 different crest. that's .0006 in diameter. I used to make a ton of parts with really oddball threads. Never used a thread gage, never had one. Jobs never had enough money in it or lead time to justify gettin gages. But we always relied on a proper pitch mic with the proper anvils, watched the major diameter, kept the rpms low enough so we didn't worry about pitch error.

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    Quote Originally Posted by fmari --MariTool- View Post
    Playing with fire. Sandvik makes a new batch, maybe .0003 different crest. that's .0006 in diameter. .
    Are not all threading inserts made at sub micron level. Why not?
    That is what I want to buy and how hard can it be. My cutting tools should be just this side of perfect in form and function..

    Bob

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    Hi mmurray70:
    How many parts will you make at a time with the same insert?
    Is the aluminum you will use particularly abrasive or is it bog standard "make a million parts without wearing the insert" aluminum?

    If you're checking parts cut from the same lot of material with the same insert and the same setup on the same day, you can probably safely infer that all threads cut with the same topping insert will be the same if the thread crests all measure good.

    Change anything and you have to gauge again.

    Just how critical are these threads?
    If you have a decent tolerance band to work with you can probably get away with it just fine.
    You did say you're gauging the first thread...how about gauging the last thread too and assuming all in between are good if the crest diameters are all good?

    So the fundamental question really is: how brave are you feeling today??
    If you don't get away with it, will you be graceful about all the scrap you just made?

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Quote Originally Posted by mmurray70 View Post
    I got a repeat job here with a 1.75 - 16 TPI external thread in aluminum. I always check the thread with gages when setting up and then use mics on top of threads to keep an eye out for changes. Seems like I always get the same measurement on top when gage is good. Tempting to just specify an OD range in my notes and go with that. Hate the feel of gages on gummy aluminum.

    Just wondering what kind of tolerance I can expect from the threading inserts (sandvik 266)? How close can I get by just measuring crest of threads? Anybody else do this or is it terrible idea?
    Terrible Idea. and a bad habit to boot.
    you should get into a standard for xx parts check x amount. ie one every x amount of parts. otherwise your running blind and hoping there all good but you have no idea if they are or not.

    BTW if your getting a gummy feeling with gages on threads in alum you may have a few issues.
    your flanks maybe running at the high limit, your finish isnt good on the flanks, you have run out or a few other things. couldnt even be your gages are worn or have alum buildup on them.
    run a little lube on the part before you put a gage on it even coolant is better than running dry.

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    But it would make life so much easier if it could be done this way.

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    Quote Originally Posted by fmari --MariTool- View Post
    Playing with fire. Sandvik makes a new batch, maybe .0003 different crest. that's .0006 in diameter. I used to make a ton of parts with really oddball threads. Never used a thread gage, never had one. Jobs never had enough money in it or lead time to justify gettin gages. But we always relied on a proper pitch mic with the proper anvils, watched the major diameter, kept the rpms low enough so we didn't worry about pitch error.
    That wouldnt be too bad. If it was 0.0006 max I could certainly work with that. Just tighten up the range a little to be safe. But who knows, inserts could vary even more then that I guess. Ive never used pitch mics before but thats not a bad idea, might check into that. thanks.

    Quote Originally Posted by implmex View Post
    If you're checking parts cut from the same lot of material with the same insert and the same setup on the same day, you can probably safely infer that all threads cut with the same topping insert will be the same if the thread crests all measure good.
    Yes exactly thats what ive been doing. Checking with gage, then mic over the top to check for variation and taper. But seems like I always get the same so just curious if this might be good enough. Ive heard tooling rep tell me once before that inserts from the same pack should be very close in size. But thats a very broad term when you think about it. How close is close?

    This application isnt super critical. Its a loooong thread for an adjustment nut so needs to be checked in several places. Ranges from 4-8 inches long. And there are several different length parts so that means moving tailstock around, and sometimes fiddling with program to remove tapers. Just measuring OD sure is a lot faster. This is part of a product we manufacture so not like I risk sending parts out to a customer that dont meet a drawing, and loosing that customer. But still want to avoid scrap in the mean time.

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    Hi again mmurray70:
    Do you get a whole run out of one edge of one insert?
    Is there typically any variability from part to part when you DO gauge them?

    I'd be pretty confident if I was using the same edge of the same insert for all parts.
    I'd be a whole lot less confident as soon as I needed to swap out inserts or even edges of inserts.
    I wouldn't be confident at all about just running to the crest diameter half a year from now using the crest diameter notes from today.

    Yeah, it's considered bad practice, but if you're making gas can caps instead of Mars Rover parts you get to apply some slack depending on how brave you are and how graceful you are about a possible fuckup.
    I would't kill myself over it one way or the other.

    Our world is FULL of assumptions and we accept many of them without much thought.
    We've all seen parts that gauged good with the fancy CMM, but then the plug gauge wouldn't go in the hole, so you could check yourself silly and still never be 100% confident all was perfect.
    At some point you have to let go...the art is to know when a cavalier attitude is going to bite you in the ass...the drawing will usually tell you that.

    As assumptions go, this isn't a bad one so yeah, I don't think I'd sweat it overmuch, especially since, as you say, they're for in-house use.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Think that this crest is on top of a triangle and not a CNMG cut.
    Stuff adds up fast here tool to tool.
    Standard make tolerance is one thou for ground. This means way, way more on the thread form.
    Some buy much tighter but this is not catalog and expensive.
    Most catalog or standards from any decent will be many miles inside the tolerance but there are times and as a maker one has room and sometimes one uses it.
    Bob

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    I do this all the time, but only with Sandvik inserts. They have never let me down, but I have been bitten by others (Vardex in particular, have proven to not be reliable for this).

    Especially on internal threads, gauging the pitch diameter is difficult. Measure the ID on every part, full check every x parts. With Sandvik 266, make the ID/OD exactly on the mean tolerance, and you can be confident the PD will be in tolerance, usually slightly on the tight side of nominal.

    As others have said, you should not use this as a replacement for full gauging, but for a quick check on the machine and instead of fully gauging every part, it's pretty safe, with Sandvik, IME.

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    Just turn the diameter to nominal, chase the thread, then measure the pitch diameter over wires using outside Mics. Whenever we do not have a gage, we always measure the thread over wires

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    Hi gregormarwick:
    You wrote:
    "I do this all the time, but only with Sandvik inserts."
    Are you confident enough using the Sandvik inserts to just go for it and trust that the thread will be good just from the OD measurement or do you still gauge the first article just to be sure?
    How much variability do you actually encounter when you change inserts from one box to another?​

    I'd have guessed they're pretty close to identical, but it sounds like you're saying they're REALLY close...like microns close, even from box to box.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Once you verify your OD pitch diameter with thread mics, thread wires/triangles and mics, or gaging, you can use the thin end of standard calipers to measure this known pitch diameter. The resulting caliper measurement value itself means nothing, it will depend on your calipers and the thread pitch. What you are doing is establishing a gaging/measurement reference.

    Using calipers to spot check the pitch diameter — verifying the known “master measurement”, between more in-depth checks, can save you time.

    ToolCat

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    Quote Originally Posted by implmex View Post
    I'd have guessed they're pretty close to identical, but it sounds like you're saying they're REALLY close...like microns close, even from box to box.
    If the boxes consecutive very likely microns.
    If a wheel or batch change there may be a bump.
    Problem being not knowing what may be in any box or even if it split across runs.
    Bob

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    This is a fantastic post !

    Are the sandvik inserts "perfect" or do you get variation in root crests, top crests, or pd ?
    How much pd variation is acceptable ?

    How on earth do you measure pd variation ?


    Quote Originally Posted by implmex View Post
    Hi gregormarwick:
    You wrote:
    "I do this all the time, but only with Sandvik inserts."
    Are you confident enough using the Sandvik inserts to just go for it and trust that the thread will be good just from the OD measurement or do you still gauge the first article just to be sure?
    How much variability do you actually encounter when you change inserts from one box to another?​

    I'd have guessed they're pretty close to identical, but it sounds like you're saying they're REALLY close...like microns close, even from box to box.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    If the thread is cut clean then a thread micrometer is just as easy to use as a normal micrometer and will keep track of variations just fine.

    Which in my view is what they are for. Relying on a thread micrometer to verify first cut thread is chancy unless the tolerances are wide enough that "nut screws on" is a good enough test. But those get done straight off the dials anyway.

    I find cut one, measure properly and use as a standard to set the thread micrometer works fine for all normal tolerance jobs. You'd still hafta do the verification measurement at each change of tooling tho'.

    The $64,000 question is how clean the cut is. Takes very little to upset measurement accuracy. Cruddy aluminium is cruddy aluminium after all so really clean cuts can be challenging.

    Frankly I suspect that the thread micrometer is more likely to be picking up variations in cut quality than any underlying geometric errors.

    Clive

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    First of all, you have to be cutting VERY small threads to be worrying about single digit microns. As in, way below the application range of laydown threading inserts.

    For a typical thread that you'd cut with even a size 11 laydown insert, if you hold crest diameter close to mean sizes, then even a 10µm variation in insert geometry is unlikely to push you out of tolerance on PD.

    I have never done any kind of statistical study to determine the limits of variation, beyond stating that, in my experience, cutting the crest diameter to mean with a Sandvik insert has always produced an in-tolerance pitch diameter, and I have done this a lot, for years.

    Marcus, yes I do have the confidence to measure a thread this way in the machine, and prove it offline. I don't tend to do that as a matter of course, but I have done it plenty of times and, touch wood, it has not bit me yet. Like I said before, it has bit me when using other manufacturers inserts, and consequently I will only ever use non-Sandvik threading inserts if I absolutely have no other option (which is almost never).

    For actual pitch diameter gauging, balls on the inside, wires on the outside, although I much prefer Marlco parallels over wires as they are less susceptible to false measurements due to form error, and the PD can be read directly without calculation. Gagemaker rolls are a functional equivalent for internal threads, although you need deep pockets for those, and they are not explicitly measuring pitch diameter.

    In many cases measuring the internal PD can be done with a single ball and a micrometer from a known concentric OD. Where that is not possible, three balls, a small grooved parallel from my gauge block accessory kit, and a stick mic. I have only ever once cut a very small internal thread where I absolutely had to measure the PD directly in order to satisfy the customer, and I used about a dozen balls, some grease to hold in them in the thread, and gauge pins. That was a huge pain in the arse, impossible to do in machine so it took two or three attempts. Thankfully most customers are satisfied with go/nogo gauges.

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    Quote Originally Posted by mmurray70 View Post
    I got a repeat job here with a 1.75 - 16 TPI external thread in aluminum. I always check the thread with gages when setting up and then use mics on top of threads to keep an eye out for changes. Seems like I always get the same measurement on top when gage is good. Tempting to just specify an OD range in my notes and go with that. Hate the feel of gages on gummy aluminum.

    Just wondering what kind of tolerance I can expect from the threading inserts (sandvik 266)? How close can I get by just measuring crest of threads? Anybody else do this or is it terrible idea?

    If your pre-turn size dropped below your cresting size, you would not get the same results.

    If you want a real cheat, always use the same calipers and stuff it down in the thread roots.
    That will not be a real size, but if you know where you are at, you can monitor "changes" that way.

    You would actually be likely to pick up slight tip wear in the root with the caliper quicker than with 3 wires as well as the wires don't set down in the root very far.



    edit:

    Looks like brother Gregory beat me to it.



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