Springfield Slim SASS #24733 Posted February 3 Share Posted February 3 My son is taking some auto maintenance/engine rebuilding classes at the local City College. He came home yesterday and wanted me to help him do the micrometer reading worksheet. When I picked up my mike and put my pinkie through the middle to hold it, he told me the teacher said that was an unacceptable way to hold it. Said you have to hold it with one hand on the bottom of the U frame on the plastic panels, otherwise body heat will change the reading, and use the other hand to work the spindle. Now, I am not a master machinist, but my father was, and that is how he said to hold a mike. Is this really a thing? Seems to me there is more error to be made by just not being consistent with tightening the spindle, hard to believe body heat will change the reading enough to matter. Just to be informed I looked on the internet, and found a video tutorial by Starrett about the use and maintenance of a micrometer, and the first thing the guy did was to put his pinkie through the U frame to hold it. So, anybody hear about the body heat problem, or is his teacher mis-informed? Quote Link to comment Share on other sites More sharing options...
Alpo Posted February 3 Share Posted February 3 I hold the bottom of the loop of the U between my left thumb and my left index finger. Put it up to what I'm measuring and turn the other thing with my right thumb and index finger. As the general rule, whatever I have had to measure sits on a base. I don't have to hold it while I am measuring it. Quote Link to comment Share on other sites More sharing options...
Springfield Slim SASS #24733 Posted February 3 Author Share Posted February 3 I'm the opposite, usually whatever I'm measuring I hold in my left hand, mostly motorcycle parts of some kind. If the piece in on my lathe I might use two hands to measure. Never worried about body heat. Quote Link to comment Share on other sites More sharing options...
Sedalia Dave Posted February 3 Share Posted February 3 From Mitutoyo As can be seen the larger the micrometer the greater the heat induced error. Although not stated I believe the above changes assume that the starting temp of the micrometer was 20C or 68F. For reference 0.0001" is 2.54 microns. Below is the complete manual from Mitutoyo E110033.pdf Quote Link to comment Share on other sites More sharing options...
sassnetguy50 Posted February 3 Share Posted February 3 Seems like the micrometer should be made of a more heat tolerant material if it experiences that much expansion over a 15° change. Quote Link to comment Share on other sites More sharing options...
Subdeacon Joe Posted February 3 Share Posted February 3 15 minutes ago, Sedalia Dave said: From Mitutoyo As can be seen the larger the micrometer the greater the heat induced error. Although not stated I believe the above changes assume that the starting temp of the micrometer was 20C or 68F. For reference 0.0001" is 2.54 microns. Below is the complete manual from Mitutoyo E110033.pdf 15.44 MB · 0 downloads Who on God's green Earth will be holding a mic for 10 minutes? And half an hour? Yeah, if you have a whole raft of parts to check you put the mic in a stand just to prevent hand fatigue. But one or two places on a part? Unless your tolerance is +/- 0.0001 you aren't going to notice. And if you are having to hold that tight you need an atmosphere controlled shop. 3 1 Quote Link to comment Share on other sites More sharing options...
Wild Eagle Posted February 3 Share Posted February 3 Expansion is possible of course, but as noted above you rarely hold the mic long enough for enough heat transfer to occur. OD mics usually have a flange to help mitigate the heat, and/or are thick enough to help. ID mics have given me more problems than OD mics. Probably due to it taking two hands and usually more time to make the measurement. 1 Quote Link to comment Share on other sites More sharing options...
Marshal Mo Hare, SASS #45984 Posted February 3 Share Posted February 3 (edited) You want to remove Murphy from the game. If the word ‘rarely’ is in your figuring, get it out of there and do as told. better yet, design a better tool or method. Edited February 3 by Marshal Mo Hare, SASS #45984 Quote Link to comment Share on other sites More sharing options...
Rye Miles #13621 Posted February 3 Share Posted February 3 11 hours ago, Alpo said: I hold the bottom of the loop of the U between my left thumb and my left index finger. Put it up to what I'm measuring and turn the other thing with my right thumb and index finger. As the general rule, whatever I have had to measure sits on a base. I don't have to hold it while I am measuring it. I’ve occasionally used a micrometer to measure the thickness of a piano string. I hold it like Alpo described above. The piece of string I’m measuring will be held in a vise. Quote Link to comment Share on other sites More sharing options...
Imis Twohofon,SASS # 46646 Posted February 3 Share Posted February 3 I worked in a factory making tungsten cores for anti-tank rounds. We worked to 50 -millions or half a ten thousandth. We were told that heat transfer was a non-issue due to the limited time in contact with the hand. And mics were held with the pinky and ring finger on the frame and the thimble turned with the thumb and index finger. For the ballisticians, it was a 4.85 pound core going 5025 FPS, that'll make major power factor. Imis 3 3 Quote Link to comment Share on other sites More sharing options...
Subdeacon Joe Posted February 3 Share Posted February 3 24 minutes ago, Imis Twohofon,SASS # 46646 said: I worked in a factory making tungsten cores for anti-tank rounds. We worked to 50 -millions or half a ten thousandth. We were told that heat transfer was a non-issue due to the limited time in contact with the hand. And mics were held with the pinky and ring finger on the frame and the thimble turned with the thumb and index finger. For the ballisticians, it was a 4.85 pound core going 5025 FPS, that'll make major power factor. Imis Yep. Plus if it's that much of an issue you are in a climate controlled shop and using a CMM. 3 2 Quote Link to comment Share on other sites More sharing options...
Marshal Mo Hare, SASS #45984 Posted February 3 Share Posted February 3 I see where The whole thing is a non issue. But I think you need to pass the course. Get some felt pads (Amazon) put them where your fingers touch the tool, BINGO, a better mousetrap. there are also many ways that one could pick apart the chart for its methodology but why waste your time. For example some folks have warm hands or cold hands (ask girl friend). Quote Link to comment Share on other sites More sharing options...
Pat Riot Posted February 3 Share Posted February 3 Wear a glove. Sounds like the teacher thinks building an engine is similar to building spacecraft. 3 Quote Link to comment Share on other sites More sharing options...
Springfield Slim SASS #24733 Posted February 3 Author Share Posted February 3 Thanks folks, I learned two things today. One, The teacher is right, heat CAN affect measurements on a micrometer. Two, it won't matter for the use I and my son will be using it for so he really needs to moderate his teaching a bit, IMHO. Quote Link to comment Share on other sites More sharing options...
irish ike, SASS #43615 Posted February 3 Share Posted February 3 Unless the shop temp. is maintained then cold and hot weather will have the same affect as your hand. I worked in an auto machine shop for 11 years. .0005 was as tight a measurement we ever worried about. Most of the time just .001 1 1 Quote Link to comment Share on other sites More sharing options...
Subdeacon Joe Posted February 3 Share Posted February 3 2 hours ago, Springfield Slim SASS #24733 said: Thanks folks, I learned two things today. One, The teacher is right, heat CAN affect measurements on a micrometer. Two, it won't matter for the use I and my son will be using it for so he really needs to moderate his teaching a bit, IMHO. Yes. And no. If he is teaching them to work in 99 44/100% of auto and machine shops, yes. He needs to get a reality check. You rarely have to hold a tolerance that close. If he's teaching the to work in that tiny portion of a percent of elite shops that specialize in optical, aerospace, and very high performance engines, then, no, he's doing it right. But, again, if that couple of microns is going to be the difference in a part passing, he needs to be teaching them how to use portable CMMs and working in a controlled environment. 1 Quote Link to comment Share on other sites More sharing options...
Cypress Sun Posted February 3 Share Posted February 3 Seems like it'd be easiest just to put it in a vise and measure at will. 1 Quote Link to comment Share on other sites More sharing options...
Subdeacon Joe Posted February 3 Share Posted February 3 Another thing to consider is the accuracy of the instrument. Going on memory here, most 1" micrometers in a shop have a book accuracy of 0.0001", unless you are getting into the $600+ range. 6" mics could be 0.0005" depending on the brand and price. The most insane thing I ever had to check was Three-wiring M395×0.5 threads while in the lathe. The range of the pitch diameter allowance was 0.004" if I recall, the 40" calipers I was using had a book accuracy of ..... you got it! 0.004". That got me looking through catalogs and the best I could find for 40" calipers was 0.002", at a price of around $6000. Which the boss didn't want to buy. 2 Quote Link to comment Share on other sites More sharing options...
Subdeacon Joe Posted February 3 Share Posted February 3 23 minutes ago, Cypress Sun said: Seems like it'd be easiest just to put it in a vise and measure at will. That's hard to do if you're trying to check dimensions in the mill or lathe before removing the part. 1 1 Quote Link to comment Share on other sites More sharing options...
Marshal Mo Hare, SASS #45984 Posted February 3 Share Posted February 3 OMG, a flashback 60 years, my toolkit in the army had a micrometer for nuclear weapons. 1 Quote Link to comment Share on other sites More sharing options...
Chickasaw Bill SASS #70001 Posted February 3 Share Posted February 3 measure with a mic. mark with sidewalk chalk cut with an axe or cutting torch good enough for Government work 3 Quote Link to comment Share on other sites More sharing options...
Marshal Mo Hare, SASS #45984 Posted February 4 Share Posted February 4 Adding a wee bit of info about the micrometer in my tool kit. First, we never used it. Sometimes took it off the board just to see how to use it if needed. It was used for rejection criteria. We inspected components for dents, nicks, or gouges, scrapes, cuts or abrasions while presumably assembling a tactical nuke in combat conditions not far from the presumed front lines. why we never used it? Do you honestly think that something that came from the factory, was only ever looked at to be inspected and have its case sanded down and repainted every two years, could possibly have damage requiring a depth check? 1 Quote Link to comment Share on other sites More sharing options...
Sedalia Dave Posted February 4 Share Posted February 4 Unfortunately this teacher is going to perpetuate less than accurate information that will be regurgitated over and over as hard fact when it is not entirely accurate. How to load shoot and clean black powder firearms is riddled with similar inaccuracies. Quote Link to comment Share on other sites More sharing options...
Wallaby Jack, SASS #44062 Posted February 4 Share Posted February 4 5 hours ago, Sedalia Dave said: ............. How to load shoot and clean black powder firearms is riddled with similar inaccuracies. There you go, ........ now you're talking "whiteman magic" ........ Quote Link to comment Share on other sites More sharing options...
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