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Measuring tool accuracy

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Peter G. Shaw04/07/2010 12:15:51
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Well, I started this thread just over 12 months ago, and never thought it would engender (now that's a word I've never used before, and don't really know where it came from!) such a correspondance.
 
Since then I've bought the 25mm, 50mm & 75mm micrometer standards from Mitutoyo and repeated the tests a number of times. Same conclusions as before which suggests that my measurement technique must be about right.
 
I've also come to the conclusion that digital verniers are a p-in-the-b in respect of batteries because I discovered somewhere that despite the On/Off button, they don't actually switch off: they only blank the display. Which means that as long as the battery is in them, they are consuming power. Same source did state that the Mitutoyo devices have the lowest current usage, but one can buy a lot of batteries for the price of a Mitutoyo!
 
Staying with digitals and batteries, I also discovered that SR44 batteries are a slightly different composition to LR44 batteries, hence have a slightly higher voltage, and hence last longer before the display starts blinking. Interestingly, the more consistent of the two electronic verniers is specified for use with SR44 batteries whilst the other one is specified with LR44! Which means that when I stop using the digital vernier, I end up taking out the battery.
 
However, I've also come to realise that the micrometer is much easier to use on external surfaces due to it's wider measuring surfaces. Also that I think that dial verniers are possibly slightly easier to use than the digitals. Certainly there is less confusion caused by the uncertainty of the last digit. Against that the digitals are more flexible with their resettable zero.
 
So, I've spent yet more money! And ok, as someone said, maybe I do have too much money, but so what, I can't take it with me. Anyway, I've now bought a S/H Starrett 25-50 micrometer, cleaned it, lubricated it (drop of 3-in-1) reassembled, readjusted and tested it. Accurate at 25mm. About ½div (0.005mm) high at 50mm. Also bought a Starrett 150mm dial vernier with a .01mm resolution. As far as I can tell seems to be accurate.
 
If nothing else, at least the vernier and the mic's are all to the same resolution.
 
I've decided to keep the good electronic vernier, & sell the poor one, but at £7.99 new, it isn't exactly going to break the bank if no-one buys it. I'm going to experiment with the old dial vernier to see if I can get the depth guage part of it to match the jaws: there's about 0.3mm difference, and if I can, then present it to my grandson who has expressed a liking for it. I'm also going to keep the slide vernier (0.05mm resolution) as for a lot of purposes it's more than adequate, and is unlikely to go faulty: the only problem is that of reading the scale - magnifying glass here I come.
 
So there we are, the end of my quest for a better comparable readings in my instruments. Does that make sense? What I mean is that I want them to all read the same, and I think I've now achieved that.
 
Regards,
 
Peter G. Shaw
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