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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?
  • what kind of material were you cutting nuguy?
    we are in the medical industy and thread milling titanium for an implant with no raised edges , frayed edges, etc
    and as i stated in an earlier thread we are checking the threads with the pitch function to a tolerence of .002" true postion
    prior to trying i would not have believed it myself.
    it has been very successful for about a year checking 32 parts a day
    nothing succeeds quite like happy numbers. extrapolate that .002 out .003, then .004, then..... chances are, that dim is over-toleranced if the part in question still works as intended. In the case of threaded holes, if your downstream customer is happy, then everyone leaves the playing field a winner.... Rolling eyes
    and (as mentioned above) while most places might use a tap? we cannot. We cut some pretty funky (proprietary) 'J' threads and I can tell you that it's no fun inspecting them. Usually split with EDM and handed off to the OGP Sunglasses
  • Sorry. I get jumpy reading thread threads. There is no wrong way. No right way. No best way. I'm going to go inspect a good and proper bore and get my sanity back.
  • Please see my earlier response. The process described would produce the most accuracy on the floor, and in quality. And the least cost effective. We machine all types of material, from exotic plastics to Inconel, as well as titanium. While I may be a putz when it comes to this software (I come to read the posts and try to learn, and you guys are outstanding!), I have a decent handle on process and maximizing quality on the floor.

    same here. i'm just trying to learn all i can and yes this forum has been very helpful.
    just noticed there were a lot of views on this thread and wanted to share what has worked for me.
  • O.K......I will flog a dead mule. I worked as a machinist for 20 years before moving into quality. Anyone who thinks that thread milling produces a thread void of irregularity is wrong. Yes.....wrong. You will still have raised edges , frayed edges, etc. Bottom line: there is no clear cut way to check thread location on a CMM, period. You can be approximate. Never exact. Which is what we strive for.
    I don't think you were getting the point. I never said anything about my method having absolute no error. I was referring to using the pitch function instead of thread locators (which using could have error too) you will never be exact with any measurement if your going put it that way. I was referring to methods that have produced me better results. and if your telling me that a thread that is produced with a tap rather then a thread mill cutter creates a better thread. I would have to disagree.
  • My two cents on this interesting thread on threads is: I only check threads as RFS on any CMM routine regardless of print callout and use the pitch option. I typically adjust the depth setting to get the truest circular size of the minor diameter and cross check with gage pins, as you guys have said impossible to check pitch dia and call that out. Fortunately for me my customers are okay with the practice and one even insists on it. And in reality it was this particular customer which convinced me to use this practice on all of my programs.

    The biggest problem I have with measuring threads in general is on a turned parts with no definite way to square to the machine from part to part. When I get parts like that I usually try to align the part on the table with the start of the thread in the same direction every time. And with these old eyeballs of mine not always consistent. Slight smile
  • Consider this, when the fastener tightens in the thread it is the flanks of the thread that contact. This contact tends to force the fastener into the center of the pitch diameter(like a taper). The minor dia does not contact. Depending on your method for thread cutting...I believe that you can actually machine a thread that is off center to the minor diameter!!
    The minor diameter is basically the tap drill size and depending on what percentage of thread you require...or whether you are using a roll or cut tap...or whether you are machining threads oversize for plating etc., the minor dia is simply the clearance size for your thread cutting tool.
  • Consider this, when the fastener tightens in the thread it is the flanks of the thread that contact. This contact tends to force the fastener into the center of the pitch diameter(like a taper). The minor dia does not contact. Depending on your method for thread cutting...I believe that you can actually machine a thread that is off center to the minor diameter!!
    The minor diameter is basically the tap drill size and depending on what percentage of thread you require...or whether you are using a roll or cut tap...or whether you are machining threads oversize for plating etc., the minor dia is simply the clearance size for your thread cutting tool.


    Nothing like resurrecting a 6.5 year old thread! Rolling eyes
  • in reply to bfire85
    It's a good little rabbit hole of a thread. The oldies are always the best. And I'll bet another 6.5 years will pass and it will be no closer to a solution.
  • in reply to bfire85
    How about a mere 2 1/2 years later? I can't wait for the next 6.5 years anniversary. I will say I'm surprised that no one informed OP that he was searching for something nonexistent. An internal "UNJF" thread for the purposes of "GO" thread gauges and Position Locators does not exist as it is exactly the same as a "UNF" thread when it comes to gauges. The only difference is the larger minor diameter to clear the larger minor diameter of the mating external thread. All internal thread gauges and position locators are manufactured such that their minor diameters would never interfere with either. When he said he understood "J" threads, he clearly did not.
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