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Thread: DRO Question

  1. #1

    Default DRO Question

    I Have a mill in my unheated garage. I would like to buy a dro for it. Will the cold weather affect the monitor or the scales? Any one have a recomondation for a dro? Thanks.

  2. #2
    Join Date
    Dec 2007
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    northwest wisconsin
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    Default

    you need to add what part of the universe you live in and what kind of temps you encounter plus what kind of mill you have, for better answers.

  3. #3
    Join Date
    Apr 2001
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    Maine
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    Default

    Temperature is certainly going to affect the DRO in terms of accuracy, and possibly in operation. It will shrink when it gets cold; how much depends on how cold it gets and what it's made of. I don't know what the coefficient of expansion for a glass scale is. If the scale is steel, like Newall's, you're talking about 6 millionths of an inch per inch per degree F.
    Some types of displays don't like to get too cold, either, or they stop working.

    I suggest you contact Mike at www.candomachinery.com and ask him. He was really good about responding to my questions, both before and after I bought an Acu-Rite DRO. He sells a bunch of the major brands and could probably recommend one for a cold environment (or tell you it's a bad idea). I also think his prices are pretty good. (Usual disclaimers, your mileage may vary, etc.)
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  4. #4
    Join Date
    Aug 2006
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    Taylorsville Ky
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    I recommend Can Do Machinery as well. I bought my Newall M20 from them.
    It's only ink and paper

  5. #5
    Join Date
    Jul 2001
    Location
    Green Bay, WI
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    Default

    The electronics can only be answered by the manufacturer
    The scales are a different story
    Steel scales, like a Newall or the Shooting Star rack expand and contract
    to match the mill, which is also iron
    That means they reflect the actual dimensions of parts at all times, assuming
    your material is also ferrous and the same temperature. ( .0000063 per inch per Deg F)

    Glass scales (Borosilicate glass) have only 1/4 the expansion rate.
    This means a steel scale 36 inches long will shrink .01134" with a 50 degree decrease in temp,matching the mill table,
    while a glass scale will only shrink.00325 thererby producing an error of .0027 inches per foot of travel

    All DRO's are calibrated for 68 degree temperature F

    Good Question

    Rich
    Last edited by Rich Carlstedt; 02-14-2009 at 11:39 PM.

  6. #6
    Join Date
    Nov 1999
    Location
    SE OZ
    Posts
    2,266

    Default Differentials in measurement

    Following on from Rich Carlstedt's excellent response.

    These are the DRO's I have (had them to over two years and haven't got around to fitting them yet!!).

    https://www.machineryhouse.com.au/Pr...stockCode=D700

    Note that they have two features that are relevant here.
    - linear error compensation; and
    - shrink compensation.

    They have an accuracy of 5 uM (5/1,000,000) metre = 5/1,000mm ~ 0.0002" (2 tenths) which is ample for most jobs and shops. Any better will require stabilised temperatures (everything at ambient), slip guages, test dial indicator (a good one) plus all compensation applied. Really better than that will require the DRO's - and perhaps lead-screws too - to "mapped".

    Its not a bad idea to at least "spot" check your DRO's occasionally as many rely on them pretty well absolutely.

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