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π tape question for gurus

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  • π tape question for gurus

    Standard outside π tape. Can they be used for inside diameters. Question came up at work. Diameter around 29.5"
    Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

  • #2
    Hi,

    Nope. They make separate ID tapes. I assume they need to account for tape thickness and then adjust the scale accordingly.

    Dalee
    If you think you understand what is going on, you haven't been paying attention.

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    • #3
      What's an n tape?
      Bill
      I cut it off twice and it's still too short!

      Comment


      • #4
        Originally posted by Seastar View Post
        What's an n tape?
        Bill
        That's Pi, not N. It's a tape that is marked to read diameter when wrapped around the circumference of something.

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        • #5
          Yes. ID and OD Pi tapes and rules. The Pi tapes/rules I have used looked like long SS shim stock and stored flat in a case like a rule. The set had 3 lengths of ID and OD. 6 total. I can't remember the maker. But it was something like Fitters Magic or something like that.

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          • #6
            OK, pi makes sense. n did not.
            Damned keyboards!
            Bill
            I cut it off twice and it's still too short!

            Comment


            • #7
              Absolutely !
              Did it all the time . Some of our steel dies were 8 feet in diameter and mikes are REALLY difficult to use on that diameter. We had multiple ways to measure parts and pi tapes play a big part when pieces get bigger than 40 " OD
              The tapes were .010 thick, so you deduct .020 from the reading. If you can lay the tape on an edge (inside shoulder) it is a snap.
              If not, then use masking tape to hold it. Our VTL machinists would first use a felt tip marker either inside or out side and hold it in touch with the part for one revolution so you had a good "level" reference for tape location.
              Be aware that Pi tapes have one horrendous advantage over ALL other measuring instruments. Thermal changes !
              A Pi Tape will quickly become the same temp as the part, and thus you do not have to be concerned with part temperature expansion during machining and having a temperature controlled environment is not a requirement. Size is immediately apparent

              Rich

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              • #8
                Eer iz wot a pi tape iz:

                https://www.google.com.au/search?q=p...HSnaDLkQsAQIPQ

                https://www.google.com.au/search?q=g...=ssl#q=pi+tape

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                • #9
                  To answer my own question yes you can . While ID tapes are recomended an outside tape can be used. Measure and add .020". But when we went and checked against calipers with long jaws (8") wegot different readings. While I suspect some jaw flex. We had the caliper's beam resting on a 2-4-6 block, a 1-2-3 block and a 1/2 ground tool bit so the jaws should of been parallel to the axis of the bore. Maybe an indicator on the beam to detect flex. It would be an interesting experiment. Oh, an OD π tape only needs 5 lbs(2.2 kg ?) tension. An inside one zero.
                  Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

                  Comment

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