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  1. #31
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    I use one of these as a comparator -
    P1010592 (Medium).JPG
    Pretty much good to the resolution of the micrometer you use then.

    Michael

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  3. #32
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    Default wotsitsname then ?

    Quote Originally Posted by Michael G View Post
    I use one of these as a comparator -
    P1010592 (Medium).JPG
    Pretty much good to the resolution of the micrometer you use then.

    Michael
    Nice gadget - wotsitcalled ? it is still going to be +/- x and the micrometer is still going to be +/- y

    if (micrometer+x) is bigger than (hole-y) then sometimes you'd be back to "fitting" together by trial and error by hand ?

    I suppose if you don't try to use the last decimal place on both gadgets, and x and y are in the last decimal place, and you deliberately make the hole slightly bigger than the plug then everything works fine.

    Bill

  4. #33
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    Quote Originally Posted by steamingbill View Post
    Nice gadget - wotsitcalled ?
    Interapid Hole and Groove Checking Comparative Gage IRA2


    Not cheap when new:
    INTERAPID IRA 2 - EuroPac Precision

  5. #34
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    Default Ducks in row

    Hi Chris,

    Quote Originally Posted by cba_melbourne View Post
    Ah, but that is still the wrong question. It still is the question that made you waste money on metrology items that are of no use to you.

    The real question you have to ask yourself is, whether or not you want or need to work to absolute dimensions.

    - If you are into machining to earn money, chances are you have no choice other than work to absolute dimensions. You work from exactly specified drawings, and cannot afford your work to be rejected.
    - If this is a hobby for you, chances are you do not want to work to absolute dimensions. You can fit things together to micron precision, without ever knowing the absolute dimensions.

    There are exceptions of course. If you are into it to earn money, but what you do resembles more blacksmithing work, you may well get away without absolute dimensions. If this is your hobby, and metrology happens to be part of this hobby, you may want to work to absolute dimensions even if it is not necessary for what you do.


    By the way, that elusive 0.001mm micrometer is just about the cheapest bit. It lets you measure shafts. But how do you measure bores, anything capable of truly 0.001mm resolution is going to cost a fortune, many times more than the micrometer. What use is that micrometer, if you can only make a shaft for a ball bearing to tolerance, but not the bore?
    You seem to have made a number of assumptions, based on my post.

    Firstly, I'd already asked myself this absolute versus relative question. I have an answer too. So, for me that was not the wrong question. For me it is one of a series of correct questions asked in the correct order.

    Secondly, I have chosen to adopt industry standard practice. To be able to measure, to one decimal point, more than the accuracy you are aiming for. Thus my 0.001mm micrometer allows me to work to 0.01mm, even if it is a little hard to read. Following an industry standard practice means I don't have to reinvent the wheel. Nor guess.

    The 0.001mm mic (New for $88 including shipping), is the cheapest piece of quality metrology I own. It is not the only piece of measuring gear I own. So when you own measuring equipment, how do you know what it's accuracy is on a day to day basis?? Note, that I am attempting to follow industry standard practice as much as possible/practical. Considerations in the decision to buy Starrett Croblox, were about the cost and disruption of sending everything away for calibration, the unknown shocks the equipment may suffer in the mail after calibration and the levels of accuracy required. I made the decision to buy a set of quality gauge blocks to check the accuracy of the other gear as and when I need to. Because of the heat and humidity I decided on ceramic rather than steel or Tungsten Carbide. The Croblox were available and suitable at the time I was looking.

    You have assumed that I have wasted my money on items that you have further assumed are of no use to me. That might well be an assumption or two, too many!

    It would be far more accurate to say that I wish quality metrology gear was cheaper.

    I don't consider any of the money I've spent on metrology as wasted. Nor do I consider any of the tools I have bought as of no use to me. In the overall context of workshop tooling and construction what I have spent on metrology isn't significant.

    By the way, the micrometer is pretty damn good when you make a shaft to fit the ball bearing you buy from the local shop who also supply you the shaft dimensions! That would be because you are working to absolute dimensions, of course!

    One day we might talk about my bore gauge, although, not today.


    Regards

    The Beryl Bloke
    Equipment er.... Projects I own

    Lathes - Sherline 4410 CNC
    Mills - Deckel FP2LB, Hardinge TM-UM, Sherline 2000 CNC.

  6. #35
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    Default

    For what it's worth, using calipers to gauge a bore then measuring the calipers with a micrometer, sub thou measurements can be made.
    Using ordinary calipers, it is written, is apparently a skill that people either have or don't have and takes a lot of practise.
    The set of calipers I have are certainly not cheapies but neither are they the most expensive.
    I won't go into repeatability though as temperature variations are going to be an inherent problem with them.
    The longer you hang onto them the more they will change at the sub thou level, but then if you were measuring at that level you would use the suitable tools.
    For what I do though they are fine, at home and at work.
    As I say guys, "for what it's worth"

    Phil
    Starrett calipers(1).jpg

  7. #36
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    Quote Originally Posted by steamingbill View Post
    It is still going to be +/- x and the micrometer is still going to be +/- y
    Yes... and no.
    Using one of these is a bit like using a telescopic gauge. You set it on the part by moving the legs until the dial reads zero then remove it, position a micrometer across the legs and wind until the dial reads the same. It can be done the other way too - set the comparator with the micrometer and then check the part for deviation. The smallest graduation on the dial is 5/10th of a thou, so getting it to read "the same as" is relatively easy.

    The advantage this (and for that matter a standard bore gauge) has over a telescopic gauge is that with these you are reading against spring tension so there is always the same pressure taking the measurement. With a telescopic gauge it relies much more on user technique. I used to find that I was usually a thou or 2 under the real diameter - not necessarily helpful when trying to get a good fit, as "usually" was not always. Here the spring force takes out the "usually" in a measurement.

    They can be found second hand (where this one came from). The important thing is to make sure you have the accessories with it - I had to make up the screwdriver / wrench for mine but fortunately it came with all the feet (mounted on the black plastic pad). Without those feet it is not much use.

    Michael

  8. #37
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    > The 0.001mm mic (New for $88 including shipping), is the cheapest piece of quality metrology I own. It is not the only piece of measuring gear I own.

    Hi Beryl Bloke, please pardon me, but after reading that price I have a suspicion.

    You said before this is a new Mitutoyo 0-25mm with with 0.001mm graduation, and that you have trouble reading the small graduations. And then you say it cost only $88 new.

    I begin thinking that what you have, is really a 0.01 graduation micrometer. I just had a look on ebay, and there are plenty micrometers in that price range on offer, advertised as with 0.001 graduation, that really only have plain basic 0.01mm graduation. This is such an example, but there are many more:
    NEW Mitutoyo 102 707 Ratchet Thimble Micrometer 0 25mm Range 0 001mm Graduation | eBay.
    or this
    Mitutoyo Japan Micrometer Scale 103 130 25 50 X 0 001 | eBay
    If you read the title it says 0.001 graduation, but if you read the print on the instrument handle itself it states very clearly 0.01mm. This is deceptive selling.

    A real 0.001 resolution micrometer looks very different to that. Nowdays most will have a digital LCD display. And he older mechanical ones were looking something like this, have a look and carefully compare the barrels to yours:
    External Micrometer - ETALON MICRORAPID 226 - EuroPac Precision
    or this
    Precision Micrometers TESAMASTER - EuroPac Precision
    or this
    Mitutoyo NON Rotating Spindle Micrometer 0 25mm Precision Toolmakers Tool NEW | eBay





    > So when you own measuring equipment, how do you know what it's accuracy is on a day to day basis??

    If you buy a good brand name 0-25mm mic (and it is genuine, not a cheaper fake) then you simply close the anvil and use the little spanner that came with the instrument to zero the reading. In industry you would regularly have the metrology department check its function and if it is worn out. In a home shop, if handled with the due care, it is likely to outlast its owner without ever wearing out. Certainly no need to have it calibrated. Chris

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