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Tru-Pos Locators UNJF thread

John Riggins
Need to measure some threaded holes 1/4-28 UNJF.
Anyone know where I can find plugs for this thread to check location?
  • In my instance checking the minor diameter location is what's needed. Besides that, the minor diameter is what is controlled for MMC. We can't change the diameter of the tap that's establishing the thread. I can't get an accurate measure of the minor diameter with a normal probe and utilizing the pitch function. It may be close, but will never be accurate.

    I could use edge and corner points for sheetmetal parts, and make my program cycle time 2-3 times longer than necessary. Supervisors don't like long cycle times when CNC machines are held up because their parts are waiting to be inspected on our single CMM and I'm taking forever to check a part with ±.030 tolerances off the waterjet.

    I'm not telling you how to do your job, please don't tell me how to do mine.

    No one here (including me) is telling you how to do your job.

    I'm just informing you of the requirements of measuring a thread for mmc as well as the limitations of a cylinder probe.
    (as others will and have)

    Grow a thicker skin.
    Everyone on this forum is just trying to help everyone else.
    If you don't want advice don't ask for it.
  • We don't. We do not give mmc bonus on threads.
    Thank Ye !
  • No one here (including me) is telling you how to do your job.

    I'm just informing you of the requirements of measuring a thread for mmc as well as the limitations of a cylinder probe.
    (as others will and have)

    Grow a thicker skin.
    Everyone on this forum is just trying to help everyone else.
    If you don't want advice don't ask for it.

    I think you may have misunderstood my previous post. I wasn't upset or trying to be snarky.

    My skin is plenty thick, working in this industry you really need to have it. I understand the limitations of the cylinder probe, I don't use it in the way that makes it inaccurate or at least how I understand it works. We make parts according to a customers print. If they ask for TP with MMC on a threaded hole, we have to give it to them. There's no other way around it. That situation is not unique to threaded holes, we get prints with requirements that were obviously the product of an "engineer" that's never seen how a part is actually made or what it takes to make that part and inspect it.

    Being a machinist by trade, I've said for years that in order to be an engineer one needs to spend a MINIMUM of two years on the floor and actually making the parts they're attempting to design. This is coming from a guy that went to school to be an engineer.
  • Ok, well, maybe there is something some of your can debate about with me, thats fine, I don't know it all, thats for sure. 99% of the time, those tru pos things are a huge waste of money and time.

    One, there is usually no reason for ridiculously close tp needs on a threaded hole. Thanks to Over-Engineers. Even with a fine thread, the accuracy cannot be too close.

    Measuring a threaded holer properly, with the correct diameter ball and the correct settings and enoughpoints will get you as accurate as using a Tru Pos.

    The cost of a tru-pos, together withthe time consumed screwing and un screwing them, just boggles my mind as to why one would use them...
  • You get no repeatability using the position locators.
    They are produced at max material condition and can be moved every time their screwed into the part.
  • Well, thanks for all of the thoughts on this subject.

    From all of this I have deduced 2 things.

    1. I don't need UN JF position locators. If I am going to use a locator, the UNF version will be adequate.

    2. I would probably be wasting time (and money) using a locator anyway. The value is dubious, depending on the particular thread and application.

    What I will do is go with probing the holes with a spherical stylus and if/when the production folks complain that I should be using TP locators, I will let them buy one and we can then determine if they make any difference.
  • very interesting thread on threads.

    we have a part with a tru pos of .002" to a 10-32 thread. Ridiculously close, yes, but it's on the drawing.
    i am checking it with a 2x20 no ext. using the pitch feature in auto circle.
    at first we had a problem with this repeating part to part. everyone assumed it was the cmm, as usual.
    found out they were only drilling the hole then thread milling.
    once they started using an end mill to bring the minor dia. to size and a more accurate location the cmm has not had any problems with inspecting the .002" tru pos.
    may not need the end mill due to thread milling, because i agree with an earlier statement that unless specified the tru pos is from the pitch. but difficult to check to the pitch.

    point is, using the pitch feature when checking a thread with a Spherical probe has worked very well for us.
  • May I throw a wrench into the fray with respect to BURRS on threads. You can use a spherical probe and the pitch feature and STILL find a burr, raised edge, etc. One may locate the thread by first boring the hole, thread milling, and cleaning any imperfections away by circular interpolation using an endmill after the fact. Then MAYBE you can use the pitch feature with some accuracy. Any engineers out there reading this? All for a threaded hole, that will most likely have play.
  • Just to jump in on the "over-engineering" bandwagon, I wanted to share the craziest print dimension I've ever seen. There is a UNJF threaded hole in a conical surface. Then, there was a true position to the theoretical intersection point of the threaded hole axis and the conical surface. The basics were drawn in a view that was 7.5*° rotated about the x-axis. Diametrical tolerance of .1 mm. We unanimously decided that achieving what the customer wanted amounted to a magic trick. Slight smile
  • Just to jump in on the "over-engineering" bandwagon, I wanted to share the craziest print dimension I've ever seen. There is a UNJF threaded hole in a conical surface. Then, there was a true position to the theoretical intersection point of the threaded hole axis and the conical surface. The basics were drawn in a view that was 7.5*° rotated about the x-axis. Diametrical tolerance of .1 mm. We unanimously decided that achieving what the customer wanted amounted to a magic trick. Slight smile
    Love it !! "Magic trick"
    LOL
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