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  • #46
    Originally posted by tomato coupe View Post
    The 3 pin method can give you the diameter for some pretty big holes, but the uncertainty is so large for big holes that it is basically useless. It's a real pain to calculate it, but you can get a rough idea by looking at the following results:

    .500 .435 .125 => calculated diameter = 5.282
    .500 .435 .126 => calculated diameter = 4.785

    So, a .001 uncertainty in the smallest pin size results in about a 10% uncertainty in the hole size. You'd be much better off using a caliper on a hole that big.
    The software written here has adjustable precision and can produce more accurate results than .001, default imperial setting was .00001". I haven't done the math to what kind of uncertainty that results in, because I don't know how!

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    • #47
      Originally posted by tomato coupe View Post
      The 3 pin method can give you the diameter for some pretty big holes, but the uncertainty is so large for big holes that it is basically useless. It's a real pain to calculate it, but you can get a rough idea by looking at the following results:

      .500 .435 .125 => calculated diameter = 5.282
      .500 .435 .126 => calculated diameter = 4.785

      So, a .001 uncertainty in the smallest pin size results in about a 10% uncertainty in the hole size. You'd be much better off using a caliper on a hole that big.



      Well you certainly aren’t wrong. But that was just a random example. Most of us would have other means to measure a hole that large.

      on the other hand, one of the nice things about measuring with pins i find is that it doesn’t take a lot of “feel” to tell the difference between the largest pin that fits and the next larger one that doesn’t. And in the example cited above, if you pick a pin that’s under by 0.001 the error is pretty obvious. You are not likely to mistake a 5.28” hole for a 4.78” one.

      but as mentioned that was just a random example. Doing a three pin measurement like this not something I need to do often it is just one more thing to have in in your toolbox.

      in my case I typically only do this when I need a specific hole in a size larger than my largest pin but smaller than I can measure closely with other means. I’ve used this for stuff like bores that I’m making for a shrink fit and need a very specific ID.
      Last edited by alanganes; 03-13-2023, 06:33 AM.

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      • #48
        I've had at least ten people request permission to rewrite my programs into more "modern" forms. I always give them my permission; after all, I'm not earning anything from them and the source code is already out there. Not one of those folks has ever returned a converted program. So, if you're wondering why I don't update the code, their reluctance may offer some explanation. I've got more interesting things to work on now. They run fine on DosBox and it's free.

        In post No. 33, Video Man says he got a 404 error while trying to access my page. If I use Firefox to access it with the unsecured "http://www.myvirtualnetwork.com/mklotz" that used to be in my sig, it works fine. I only recently learned that the secured form, "https://www.myvirtualnetwork.com/mklotz" is needed in some browsers. My sig has now been changed to reflect that fact.​
        Regards, Marv

        Home Shop Freeware - Tools for People Who Build Things
        http://www.myvirtualnetwork.com/mklotz

        Location: LA, CA, USA

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        • #49
          I can send you back the source code if you like to look at it. I'm new to C programming so don't expect anything brilliant however.

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          • #50
            Originally posted by luthor View Post

            Much easier said than done.
            Originally posted by J Tiers View Post

            Why do you think it is so difficult?

            Think about it as I suggested.....

            I think that it would work very well. Two accurate pins would fit with NO movement around possible. But undersize would be able move. Not AS accurate as 3, because of need to judge movement, but close enough for me. If I had gauge pins.

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            • #51
              Originally posted by DennisCA
              The software written here has adjustable precision and can produce more accurate results than .001, default imperial setting was .00001". I haven't done the math to what kind of uncertainty that results in, because I don't know how!
              Changing the "precision" to .00001 in the program doesn't do anything for you, unless you have pin gages in increments of .00001 and you can tell whether .12500 or .12501 (for example) is the correct pin.

              Originally posted by alanganes View Post
              Well you certainly aren’t wrong. But that was just a random example. Most of us would have other means to measure a hole that large.

              on the other hand, one of the nice things about measuring with pins i find is that it doesn’t take a lot of “feel” to tell the difference between the largest pin that fits and the next larger one that doesn’t. And in the example cited above, if you pick a pin that’s under by 0.001 the error is pretty obvious. You are not likely to mistake a 5.28” hole for a 4.78” one.
              You're missing the big picture. The number generated by the program when measuring a very large hole is essentially meaningless, because any uncertainty in determining the correct pin size leads to a huge uncertainty in the hole size. Again, for that 5" hole, even if you had a set of pins in .0001 increments and you could determine the correct pin at the .0001 level, the uncertainty in the hole size would still be about .05". You could do better with a steel rule.

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              • #52
                Originally posted by Bob Engelhardt View Post




                I think that it would work very well. Two accurate pins would fit with NO movement around possible. But undersize would be able move. Not AS accurate as 3, because of need to judge movement, but close enough for me. If I had gauge pins.
                Well, ONE person got it correct. Good for you!

                Yes, the use of three pins on a hole much larger than the pins fit closely in, is inaccurate in practice, no matter how accurate it might theoretically be per geometry.

                It's a reversed version of the "difference of large numbers" issue, where the pin fit is the "difference" Since the "difference" is only known to a certain accuracy, the two large numbers (two diameters near the true diameter) can differ by a multiple of the pin accuracy.
                CNC machines only go through the motions.

                Ideas expressed may be mine, or from anyone else in the universe.
                Not responsible for clerical errors. Or those made by lay people either.
                Number formats and units may be chosen at random depending on what day it is.
                I reserve the right to use a number system with any integer base without prior notice.
                Generalizations are understood to be "often" true, but not true in every case.

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                • #53
                  [deleted]
                  Last edited by thin-woodsman; 03-25-2023, 11:45 AM.

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                  • #54
                    Back to the subject of gage pins & how useful, I have pins from 0.060 up to 0.749 (set is missing the 0.750). I purchased mine at auction, focusing on sets where a few pins were missing - the sets tend to sell for much cheaper (I have bought partial sets for as little as $ 5 to $10 for 1/4 to 1/2 dia pin set with say 10 pins missing). I am not to worried about missing a singular pin - I can interpolate between a missing pin for my needs as a hobbyest - if two or more adjacent pins are missing I tend to fill in every other pin as a minimum. Since I refuse to pay for Amazon Prime, I will typically add a missing gage pin or a x/64 5c collet to my purchase to bring the total order above the $25 threshold for free shipping when making a small Amazon purchase.

                    I bought a 0.7 to 1.4 inch bore gage. I am still learning to use it. Not nearly as fast as opening a gage pin set and pulling out a pin or two. One of the sets of pins had been (shop) engraved with the size on the ends of the pins - I have now done so with the remaining sets for dia over about 5/16 inch. Easier to pick a pin out of the set. Some of my sets have the size below the pin, others have it above the pin - don't have to look closely if the pin has the size engraved on the end.
                    Last edited by aribert; 03-14-2023, 01:56 PM. Reason: typo
                    Metro Detroit

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                    • #55
                      Out of all the tools posted here, these are a best buy.
                      I have .011 - .500 SPI . 3 boxes made of metal. Endless usage, sine plates, hole pickup, odd size dowel pin ( yes they are cheaper than making one ) and more. Congrats on your new tool.

                      Click image for larger version

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                      • #56
                        Originally posted by Fasturn View Post
                        ..... Endless usage, sine plates, hole pickup, odd size dowel pin ( yes they are cheaper than making one ) and more.....
                        Your posting reminded me of an example where I harvested a couple of gage pins to use as dowel pins. New Years Eve morning I pick up a flywheel that I had resurfaced at the local automotive machine shop. I forgot to make sure the (3) 6 mm dowel pins for the pressure plate to flywheel alignment were picked up with the flywheel. By the time I noticed that the pins had been left behind, the machine shop was closed and I wanted to finish the clutch replacement that afternoon. I cut the two closest inch gage pins in half and used 3 pcs for the alignment pins. I just did another clutch replacement on the same vehicle this past fall and the gage pins are still there aligning the pressure plate. Yes, I could have turned 3 pins but it was faster to chop up some gage pins and order new ones later.
                        Metro Detroit

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