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  • Telescoping gauges findings/questions

    I bought a cheap set of telescoping gauges from amazon a few months back and haven't had much need for them, at least for high accuracy. I've played with them some and have had decent results with what I've been working on, but recently have had the opportunity to explore more. My work (engineering office not machine shop) just bought a set of Mitutoyo ones and I was giving a presentation to a group of young teens on precision measuring so I had a chance to play with both sets side by side. First my experience was that they are nearly identical, I see no need to spend the money on the current Mitutoyo offerings.

    My real issue is with the technique I've come to understand. Both sets of gauges when tilted through the bore will spring back and read large. I happen to have a pinion shaft and bearing out of my old truck as a book end, perfect training aids. Measuring the bearing ID with the TS gauges I consistently got readings larger than the design bore and the shaft. I knew the bore was smaller than the shaft because I had to press it off and it won't go back on by hand.

    What I found with both sets of gauges is that neither hold their size when compressed while locked, lightly or tightly. There is not a good one-way-clutch action as would be required for this technique. After tilting the gage through the bore, you can never re-insert the gauge into the bore straight, it's always too big, as my measurements found.

    With some experimenting I found I can get results within +- a tenth by holding the gauge as straight as possible in the bore, and then locking it. This eliminates the need to push the plungers against the lock and therefore spring back. You can then feel the gauge in the bore to make sure you got it right. The bearing is a used Timken, but has a bore tolerance of -0 +0.0005", and I could very repeatability hit this range with this method. With the standard method as I said I was always over not only this range, but also the shaft size, which was another 0.0004" above the high end bore tolerance.

    Any similar experiences out there, or comments. For my use I'll keeping my cheap gauges and will adjust my technique to suit, just wondering if anyone else has come to a similar understanding.

  • #2
    I have reasonable success with those gauges. I totally collapse then and lock them, insert them into the bore and unlock them. I swing them to the left a little bit, then to the right a little bit, then hold the handle concentric to the bore and lock them, then pull them straight out and measure them with a micrometer. When in doubt I measure 3 times and take the average.
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • #3
      Dan's the man (at 6:45): https://www.youtube.com/watch?v=zv6NUyFbWEQ

      Ken

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      • #4
        Hi,

        When you absolutely need to know the bore diameter, there are far better tools to use than telescoping gages. Their biggest claim to fame is that they are cheap to buy and generally good enough for most accuracy. I can comfortably measure +/- .001 as a rule, but anything less is iffy at best. Give me a good B&S Intermic set for that. But at $1000 a pop, it's kind of hard to justify. Even a dial bore gauge with a setting ring is better.

        They do take a good amount of practice to master. The tilt, snug, and swipe upwards works pretty well and is the accepted proper method of using them. But your method can also work. If you are happy doing it, do it. As Brian mentioned - always, always take multiple readings with telescoping gages and average them.

        Cheap vs expensive telescoping gages? I'm kind of like you. I don't think it matters too much. I've been rocking the same no-name Enco set I bought 30 years ago. They are every bit as good as any big name brand I've used as long as I use them correctly.
        If you think you understand what is going on, you haven't been paying attention.

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        • #5
          I don't know where that 'tilting through the bore' thing came from. I wasn't taught that way 40+ years ago and I'd never do it now. The radius on the ends of the plungers is critical, and dragging the ends regularly with lock pressure has to wear on them.

          I do much as the OP later said: Line them up with the bore as much as possible, wiggle a bit, then lock, withdraw and measure. Easy to get within a tenth or so.

          It takes a gentle touch and a bit of finesse which horsing it through the bore does not provide.
          Southwest Utah

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          • #6
            Thanks for the input guys. For what I do I'm more than happy with the set I have, and really glad I didn't spend more. I did make a replacement bushing for one of my lathe gears last week and it pressed right in with a bench vice. That was a small bore so the technique was more of a pull straight out anyway.

            I was just really curious about the lock then tilt through the bore technique. It just doesn't work on one pass through with either of these gauge sets. I swear I've read that, and seen it in videos, but what you say makes perfect sense to me chipmaker.

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            • #7
              A lot of the cheaper ones arn't very accurate. The extensions wiggle a bit in the bores and give false readings, This may lead to not being able to get repeatability. Better quality ones are more accurate. Accuracy costs.
              The shortest distance between two points is a circle of infinite diameter.

              Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

              Southwestern Ontario. Canada

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              • #8
                do the cheap ones have the same radius on the tips for all sizes? i would think mitutoyo doesnt.

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                • #9
                  My cheap ones appear to have different tip radii yes. The fit and finish on them seems pretty decent, and the lock feel was very similar to mitutoyo. Neither has a setting where you can move the plungers after you lock it and have it stay at the new position, which is what the method I had understood to be proper would require. Both are easy to lock up tight if you are on size to start with.

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                  • #10
                    Telescoping gauges are just plain tricky and for all kinds of reasons mentioned,

                    plus keep this in mind - also depends on the material your measuring against and it's surface finish,,, those light duty springs may not seem like much but they are actually exerting some very high unit pressures on those little ball ends,

                    so the results when measuring things like aluminum or even cast iron after say something like a cylinder bore was honed or the like will most likely almost always read a little large, not really the gauges fault as it's being pretty accurate in fact in a honed type situation look at the bore after checking and you will see little "drag marks" of the balls flattening out the hone, aluminum is way worse esp. if the finish is a little coarse, iv gone as far as taking .003" feeler gauge material and placing it in internal surfaces on both sides and then adding the tolerance after the measure, to me there is no other measuring device that takes more fumbling around with to come up with a fairly accurate conclusion, but the more you play with them the better you will get and the more it all makes sense.

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                    • #11
                      Originally posted by chipmaker4130 View Post
                      I don't know where that 'tilting through the bore' thing came from. I wasn't taught that way 40+ years ago and I'd never do it now. The radius on the ends of the plungers is critical, and dragging the ends regularly with lock pressure has to wear on them.

                      I do much as the OP later said: Line them up with the bore as much as possible, wiggle a bit, then lock, withdraw and measure. Easy to get within a tenth or so.

                      It takes a gentle touch and a bit of finesse which horsing it through the bore does not provide.
                      Hi,

                      The ends are supposed to be hardened and ground. It will take a lifetime or maybe two to incur measurable error in the radii on the ends. Even if not real hard, you simply won't use them enough to need to worry about it.

                      The tilt and sweep thing is something found in textbooks and I think I even read it in a Starrett pamphlet too. I've used both techniques and find them to be about as easy and accurate as can be expected. The tilt and sweep method is generally faster as less "fiddling around" to get the right feel is needed. Speed can matter when money is on the line.
                      If you think you understand what is going on, you haven't been paying attention.

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                      • #12
                        Forrest advocates the tilt through technique.

                        I had a heck of a time getting a measurement within 5 thou for a long time. I was ALWAYS about 5 thou 'off".

                        THEN eventually the penny dropped..... I took a good look and found small flats on the ends of several of them. NOT wear, they were obviously just a bad manufacturing issue.

                        I replaced the bad units, and can get under a thou with them now.

                        If you want, you can do several measurements, and take an average. That will probably get closer to the true value than any single measurement does. Throw out any obviously wrong values before averaging.
                        CNC machines only go through the motions

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                        • #13
                          I have a set of Starrett telescoping gages that I've had and used for over 20 years. I've never found anything to complain about with them.
                          It doe's take a little bit of practice to get the feel for what your doing with them, but I get accurate and repeated measurements to .0005 every time.
                          The surface finish of the hole your measuring has a lot to do with the accuracy and repeatability of your reading. Rough turned holes in material that has poor machining qualities tends to give less accurate readings for various reasons.2
                          As far as trying to insert the gage back into the hole...... awful tricky as you have to hit the center lone of the hole just right and that's not likely to happen.
                          When I take a measurement with one I wiggle it from side to side a bit so it'll center and then try to eyeball the stem as straight as possible before locking it. That takes a bit of feel too as it's easy to tilt the stem out of line or apply pressure to one side of the gage resulting in an inaccurate measurement. I always take a couple readings just to make sure.

                          JL...................

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                          • #14
                            Take several readings and average them? I'm not so sure that's good technique.

                            Consider: any tilt error in measuring the bore will result in error on the plus side. So I take several readings and select the smallest one - no way alignment error can make the measurement too small, is there?

                            BTW, I have a set of Starrett gauges and a set of no-name imports. Both work well.

                            -js
                            Last edited by Jim Stewart; 04-27-2018, 04:09 PM.
                            There are no stupid questions. But there are lots of stupid answers. This is the internet.

                            Location: SF Bay Area

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                            • #15
                              Hi,

                              Averaging isn't perhaps the best term. It's more of looking for repeatability than anything. If you get a couple two or three measurements that are within a few tenths, you can be pretty sure you've got a decently accurate measurement.
                              If you think you understand what is going on, you haven't been paying attention.

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