Buying mics on a budget

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    Default Buying mics on a budget

    I'm a hobbiest that does some side work now and then so buying a set of new mitutoyo/starret mics is more than I want to spend. I've found that certain cheap import things are ok, others not so much. I do have a 0-1 digital mic that I bought from harbour freight about a year ago and it has been fantastic. Believe it or not, but it will nail single microns all day long. I do have a decent set of gauge blocks for qualifying. I tried again with a 60 dollar set of 4 vernier mics (0-4") and they are garbage. The surfaces were ground out of parallel so it's not possible to get consistent measuring better than a thou or so. Luckily harbour freight has a no questions asked return policy so I dont mind trying out their stuff, sometimes you get lucky.
    Im currently rebuilding/modifying part of my machine and I need some precise measuring greater than an inch. Right now I really only need to add a 1-2 mic and can get more later. I think I would pay probably 75 bucks for one. Question is, should I try some other higher quality imports, or go with a used mitutoyo or starret? Ive already found a couple on ebay in the price range I'm willing to spend. I would really like the ability to measure within 1 micron consistently (roughly half a tenth) Any advice on this subject?

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  2. #2
    Community Moderator Jim Dawson's Avatar
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    Default Re: Buying mics on a budget

    When you start trying to measure +/- 1um, you need to ask at what temperature. Just because the instrument displays 4 or 5 digits to the right of the decimal point does not mean that the measurement is anywhere close to that. In the home shop or even on the factory floor, the best you can realistically measure is about +/- 0.0002'' ~0.005mm To get closer than that requires a metrology lab and closer than that is just not needed in most applications.

    As you stated, parallelism of the anvals is what is the most important for accuracy.

    I have a set of SPI digital mics that seem to work OK, and seem to match my cheap gauge blocks, but I'm not doing work for NASA. The most critical thing I normally do is getting shaft fits in bearings and have had no problems.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Buying mics on a budget

    My basis for stating my 0-1 mic can hit microns all day is not an assumption based on the amount of digits it reads, rather what I'm reading when I put it on my gauge blocks. I have a metric set of blocks that I can ring together in various combinations under 25mm and my mic consistently reads them within a micron of what they are supposed to be. I'm sure things change drastically at larger distances and it's much more difficult to get readings that consistent. I also have my mic and gauge blocks stored on the same shelf, so temp variance applies to both. I'm also keeping temp in mind when trying to get a good measurement, I try to avoid wrapping my warm hand around the body of the mic for too long.
    But anyway, fully understood that temp plays a big role and maybe expecting micron accuracy on larger mic sizes is asking alot in anything short of a lab setting with temp control. I guess what I'm mostly wondering is if I will have better luck buying an excellent quality mic that is used, or a less popular mic that is new. I'm still a bit fresh as a machinest, 2 or 3 years now, so I'm not sure what to expect with used mics. Does a good mic typically hold accuracy? Does the screw wear and read differently at more common measurements? Will a mic that gets dropped on the floor lose parallelism of the anvals?

    Edit: did the math since I was curious. A 1 inch steel block with change 1 micron per 6 degrees F, so as long as the Mic and the object being measured are within a few degrees, it shouldn't be hard to get micron consistency in these smaller sizes.
    One more thing to add, I'm also not looking to make parts better than 5 micron accuracy, even 10 or 20 in most cases, but the one thing I need to be more accurate than that to do so is my machine. I really want to get this thing as dialed as I possibly can, and In a few cases I can run into tolerance stack so I really need to be able to measure as good as possible.

    Last edited by QuinnSjoblom; 10-21-2020 at 03:10 PM.


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    Community Moderator Jim Dawson's Avatar
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    Default Re: Buying mics on a budget

    I do have a 0-1 Mitutoyo mic that I have been using for the last 40 years. Been dropped more than once, but still seems to be accurate. I also have a set of old Taiwan mics about the same age, and they seem to be accurate. But neither is electronic digital. It is possible to read them to 0.00005'' by interpolating the vernier. But can they repeat that accuracy? That is really a matter of how sensitive your fingers are when you turn the barrel. That just takes practice to do it the same way each time. I normally just drag my finger across the barrel as I wiggle the mic a bit. I get pretty consistent readings that way.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Buying mics on a budget

    Ok, I might give a used mic a try. I found a lightly used mitutoyo 1-2 for 55 bucks. Who knows what "lightly used" actually means, but it at least looks new in pics



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    Default Re: Buying mics on a budget

    Used mitutoyo 1-2 showed up yesterday. Definitely a good buy for 50 bucks shipped. Looks and operates like brand new. I think ill continue to watch for high quality brands that are used, no more super cheap import stuff. I need endless metrology gear. 4 more mics at least, height gage, indicators, gauge pins, surface plate, squares, big straight edge. Just goes on and on. Kinda need it all if you want to build accurate machines.



  7. #7
    Community Moderator Jim Dawson's Avatar
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    Default Re: Buying mics on a budget

    It's never ending, you always ''need'' that one more thing. I have purchased all of the stuff you listed above, in multiples. If I had room for one I would have a CMM. Do I need one, or even effectively use one? No, but they're cool.

    I keep my eye on the local Craigslist and buy good deals when I find them.

    Jim Dawson
    Sandy, Oregon, USA


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