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  • Leaving micrometer damage

    I'm a bit embarrassed to be asking this question after all these years, but whenever I use a micrometer or even dial calipers to measure a diameter, I worry about leaving small marks on the workpiece surface from the hardened micrometer pads. Miking a crankshaft journal is a good example. What's good general advice for this situation ?

  • #2
    +1 for Tiffie

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    • #3
      Bill
      I worked in a automotive machineshop for over 25 years and mic'd a lot of crankshafts. The first thing i always did when measuring a crankshft was to wipe off the faces of the mic and wiped the crank journals to make sure they didn't have any dirt or grit on them. I would assume that one would just naturally do that on any item and that would take care of your concerns.
      Gary

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      • #4
        It's an easy fix. You just go to your local Home Depot or Lowes and get some of those little felt dots meant to put under coasters and the like. You stick one to the barrel and one to the anvil of the mic, and voila! A scratch-proof micrometer.

        That one needs to go in a "shop tips" book somewhere.

        Doc.
        Doc's Machine. (Probably not what you expect.)

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        • #5
          But don't forget to subtract the combined thickness of the dots from your measurements!
          Lynn (Huntsville, AL)

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          • #6
            Micrometer

            Mark one up for Doc... Great.

            JRW

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            • #7
              Originally posted by J. R. Williams
              Mark one up for Doc... Great.

              JRW
              Hmmmm to me it sounds like doc is yanking our chains, To me it would seem that the felt would be too squishy to get an accurate reading, Not at all positive, but it sounds a might strange . . . .

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              • #8
                Originally posted by fredf
                Hmmmm to me it sounds like doc is yanking our chains,

                YA THINK?.......................
                CNC machines only go through the motions

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                • #9
                  In the rare cases where marking or deformation is a problem (typically soft materials), shops use mics with non-rotating spindles. These will sometimes come with larger diameters (to spread the pressure) and sometimes with spring-loaded anvils (which control pressure even better than ratchets or friction thimbles).

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                  • #10
                    Originally posted by Bill736
                    I'm a bit embarrassed to be asking this question after all these years, but whenever I use a micrometer or even dial calipers to measure a diameter, I worry about leaving small marks on the workpiece surface from the hardened micrometer pads. Miking a crankshaft journal is a good example. What's good general advice for this situation ?
                    If you are leaving marks or displacing metal with a micrometer, then there is grit in between the piece and the mic or you are using it as a C-clamp.
                    Amount of experience is in direct proportion to the value of broken equipment.

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                    • #11
                      If you're overly worried, I'd toss a piece of delrin in the mill, mill a channel and tap a hole to clamp it onto the ends of the tool. Subtract the thickness for a mic, or re-zero calipers. Mill flat and re-zero when necessary.

                      99% of my machine work is with aluminum, and I've used my mic and calipers on cast lead to make sure it wasn't out of round, with no ill effects. What are you doing with the poor thing?

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                      • #12
                        Originally posted by fredf
                        Hmmmm to me it sounds like doc is yanking our chains, To me it would seem that the felt would be too squishy to get an accurate reading, Not at all positive, but it sounds a might strange . . . .
                        Not at all. It's a very old trick. In the beginning of the 18th century a soviet machinist suggested duct taping micrometers. Within about ten years use of Home Depot sticky felt was proposed in Eastern Germany. That's how I used my mics until I found a more contemporary approach. I just bought a jar or Plasti Dip and coated all my mic anvils/barrels and caliper jaws. Metric tools received red coat, imperials got blue one. Since this is, virtually, a permanent solution, you'll save a lot of money by not buying the sticky felts.

                        My next weekend project will be coating my edge finders and micrometer standards with Plasti Dip. Then I'll apply a layer to my surface plate to prevent any dings and scratches. And I'm thinking about using it on my lathe tools, drill bits and mills to virtually eliminate their wear.

                        Last edited by MichaelP; 12-18-2011, 05:36 AM.
                        Mike
                        WI/IL border, USA

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                        • #13
                          Doc forgot to say that you need to recalibrate the micrometer by closing it against the felt pads using the thimble, in order to compress the pads, then you adjust the mic to read zero using the pin spanner provided.

                          Phil

                          Originally posted by fredf
                          Hmmmm to me it sounds like doc is yanking our chains, To me it would seem that the felt would be too squishy to get an accurate reading, Not at all positive, but it sounds a might strange . . . .

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                          • #14
                            Plasti-dip! Why didn't I think of that....!

                            The other trick for a micrometer is to slot and drill both the anvil and the ram for rollers, like miniature versions of a roller lifter.

                            That way, you can mic parts in the lathe without stopping the chuck- which, as you might imagine, would be a huge time saver.

                            (pat. pending)

                            Doc.
                            Doc's Machine. (Probably not what you expect.)

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                            • #15
                              It is a little known fact that the first instrument of this kind, invented by Michael R. Ometer, in fact had a balsa wood spindle tip and anvil to keep from marring the surface being measured. The instrument achieved great success its only drawback being that the spindle tip and anvil would have to be replaced after each reading. Needless to say Mr. Ometer's business did fantastic volume in spare parts.

                              Mr. Ometer's chief competitor, Mr. Vernon Eayre's own instrument of a fantastically different design was losing market share to the new instrument and Mr. Eayre secretly invested a small amount of money in a company which produced non-balsatized spindles and anvils to compete with Mr. Ometer. This foray into the world of venture capital was to Mr. Eayre's eventual regret however for the 'Maintainable Instrument of Calibration' (or Mic) soon dominated as the measuring instrument of choice among machinists worldwide.

                              SIDENOTE:
                              Mr. Joseph Blocks, the gentleman whose gages were used to calibrate both instruments was heard to say, "I don't care which of these guys sells the most instruments as long as I get to eat." (He was standing in line to enter a Chinese buffet at the time)
                              Last edited by DATo; 12-18-2011, 08:37 AM.

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