How to read a vernier scaled bore gage

I've got a new job working for a shop that repairs a certain kind
electro/mechanical unit off of big commercial aircraft. The shop is part of
the company that manufactures these units new. We tear down, inspect and
rebuild these units that come in from all over the world. Today was my
second day on the job. The guy training me is showing me how to use a bore
gage that uses a micrometer type vernier scale and has the three little
anvils that come out to touch the walls of the hole. On one job the guy
tells me one reading, and the next he tells me another. He's going so fast I
hardly have time to realize what he is doing, let alone being able to look
closely enough at the bore gage to check his reading. Besides its been a
while since I've read vernier scales. Got to get the old brain back into
that mode. Break time rolls around and I pick up this bore gage and put it
into the standard as a check. I'm talking to the other worker sitting at the
bench next to me trying to think out loud with him to either confirm or deny
my suspicions that the guy training me is either confused, confusing me or
totally reading it wrong. Making a long story somewhat shorter, soon I've
got a few guys telling me to "do it the way we show you"; basically that I'm
a newbie and don't know jack. But I try to explain to them that the way they
are doing it that by the time you screw the thimble in two full turns to the
next whole unit that they would only be reading a tenth of that. Basically
they were one decimal place off. They were reading the hundredths as
thousandths. Makes you wonder how many aircraft parts get rebuilt that
shouldn't have been because they were out of spec and nobody caught it. The
one who got into my face did apologize later in the day. But I walked out of
there today really wondering what I've gotten myself into.
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That really sucks, being in that position when new at a job.
FWIW the biggest source of scrap parts at my former production job was somebody doing *just* that, reading a micrometer one turn or one division off. So the parts would be all the same size, just the wrong size.
The management there took a great deal of pain to see that folks were trained on the measuring tools, and also to detect if anyone had a handicap in this regard.
One of the easiest ways to do a sanity check was to directly compare one instrument with another one, with the second one being a digital caliper. The caliper of course could not measure as well as some of the other instruments but it could certainly detect when things were off by 0.025 inch!
I think you did a good job of pointing out the error and still keeping your wits about you when the goofup kept insisting 'my way or the highway' - especially when "his" way was flat-out wrong!!
Bonus points for tact and diplomacy go to you.
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jim rozen
Im just guessing but im inclined to think that the vernier scale is reading the tenths. .xxxx
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Basically one guy was totally ignoring the vernier scale part. He thought that it was for the fourth digit in the reading: i.e. .0001 and wasn't important for the reading at hand, even though the vernier scale was marked ".001".
Part of the story that I left out was, that another employee who overheard all of this, but doesn't work on the same equipment came over with a shop "how to" book that explained everything and backed me up. Everyone ended up apologizing to me by the end of the day.
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Thanks, but all the same I wish that it didn't have to happen. After lunch, the guy training me said: "you came back?"
I don't know if there is another bore gage in that range or a digital caliper in the shop to compare it with. That is a good idea however, I'll have to ask about that.
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what is the make & model of the bore guage that you are using?
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All I can tell you right now is that it is a Mitutoyo 10-12mm. I will look at it better on Monday.
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One job I had a few years back I caught one of the old timers doing something wrong. When I corrected him he jumped on me stating "I have been doing this for twenty years, don't tell me how to do my job!" I just looked at him ans said " It's about time you started doing it right!" Needless to say he got a little pissed at me, but in the end he calmed down and corrected himself! Greg
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Greg O
In that case, the gauge was reading in 0.001mm not 0.001". (And 0.001mm on the vernier is about 0.000,003,9 " -- a *lot* finer than 0.000,1".) The 0.01mm on the dial itself is 0.000,39" -- about four ten-thousandths. The range is 0.3930"-0.4724".
That sounds like the Mitutoyo equivalent of the B&S/Tesa Tri-Mike. I have quite a few in various inch sizes, and one in metric. (And one of the ones in the inch sizes happens to be a Mitutoyo.) The dials on the Tri-Mikes are marked in 0.000,2" graduations, without the need for a vernier. Some are even marked in 0.000,1" direct graduations, IIRC.
All are very nice tools.
Enjoy, DoN.
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DoN. Nichols

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