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A cylindrical probe which will take more accurate hits on thread holes.

Bill G
That's the email I got upon entering the shop today. I was using a 1 x 10 styli for a part with 3-48 & 6-32 threaded holes. Just trying to get a decent location within tolerance of +/- .005. Now, the customer (we are the sub-contractor) is "coming in today with a cylindrical probe which will take more accurate hits on thread holes". I checked some of the postings in the forum and it looks like there's a lot involved and the results are sketchy.
  • I appreciate all the great technical advice. I really appreciate it.
  • Unless you use Pitch in the auto circle to follow the threads spiral/helix.
    +1 I use the ruby ball probe and use the pitch function seems to work and if your threads are clean (no burrs ect.) It should not matter where it makes contact in the threaded hole as it should follow that same pitch.
  • I hate to throw a wrench into this thread, but I can give an example for why each and every method has it's inaccuracy's, from why pitch/auto circle is flawed to why threaded posts will be pulled one way or another. The hole must be BORED and the thread fabricated using a THREAD MILL to produce the most accurate location, yet a burr from the thread mill will skew any attempt at using the auto feature to check location of the thread. I could go on and on.
  • Thread locators are the only way I am aware of to measure off of the pitch diameter, which is what is required per ASME Y14.5... It's funny that a shank probe was your customer's best answer to your problem...

    Measuring off of the minor with or without the pitch function turned on still violates the standard. I generally only use our locators if the position tolerance is tight or if it is close to the edge of the tolerance. They are very handy but can tie you down to the CMM when measuring parts with a lot of threaded holes.
  • How about this http://www.trueprecisioncorp.com/MultiBallLocationGage.pdf NUGUY ? Seems to be the most accurate on the market for checking the "actual" thread location.

    There is always going to be measurement uncertainty.
  • A "shank" probe will only give you the location of the minor diameter. I have watched thread locators pulled to one side, for a variety of reasons. How would one check an 0-80 thread using auto-circle/pitch, or similar threads. Engineers truly need to stop attaching unrealistic tolerances to thread locations. My favorite is when they attempt to apply MMC to a threaded hole. Good luck with THAT one.
  • BTW, don't make the typical "rookie mistake" and enter the pitch in backwards. Always remember the Right-Hand Rule: With your right hand thumb pointing in the POSITIVE direction of the Z-axis (or whichever is your axial direction), a POSITIVE rotation follows in the direction that your other 4 fingers are pointing. I've seen more programs with the pitch entered backwards than ANY other common CMM programming error...
  • BTW, don't make the typical "rookie mistake" and enter the pitch in backwards. Always remember the Right-Hand Rule: With your right hand thumb pointing in the POSITIVE direction of the Z-axis (or whichever is your axial direction), a POSITIVE rotation follows in the direction that your other 4 fingers are pointing. I've seen more programs with the pitch entered backwards than ANY other common CMM programming error...

    Like I said - I check visually on the path lines, and watch as it executes just to make sure.
  • A "shank" probe will only give you the location of the minor diameter. I have watched thread locators pulled to one side, for a variety of reasons. How would one check an 0-80 thread using auto-circle/pitch, or similar threads. Engineers truly need to stop attaching unrealistic tolerances to thread locations. My favorite is when they attempt to apply MMC to a threaded hole. Good luck with THAT one.

    and yet it continues to happen, day in, day out. <facepalm>
  • A "shank" probe will only give you the location of the minor diameter. I have watched thread locators pulled to one side, for a variety of reasons. How would one check an 0-80 thread using auto-circle/pitch, or similar threads. Engineers truly need to stop attaching unrealistic tolerances to thread locations. My favorite is when they attempt to apply MMC to a threaded hole. Good luck with THAT one.

    and yet it continues to happen, day in, day out. <facepalm>

    Yes. Discussing this with an engineer on the yahoo Y-14.5 board one day, I was told, 'Engineering design should not be restricted by what manufacturing and inspection are capable of. It is their job to make and inspect what we design.' Rolling eyes

    If you really want to have some fun, look into SYSTEM 21 vs. SYSTEM 22 thread inspection.

    for example:     http://www.johnsongage.com/technical.shtml


    Thanks again for everything Ironhoe.

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