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  1. #1
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    Default Change Units inch to metric in the middle

    Hi guys,

    I'm picking up autocad using autocad 2010 version.

    Lets say a drawing's unit is mm, and now I change the unit to inch.
    I know if we just change the unit at beginning, all the lines of the drawing will be base on that unit.

    How bout if we change the unit to another along the way?
    will the drawing's measurements such as angle and annotation dimension be affected too?

    I know it's sound silly to ask this. But I was curious about it will it create huge changes or some changes we can't notice it easily?

    Thanks in advance!
    chewy

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    I would think that changing units midstream, an inherently bad idea, would cause changes that might not be easily noticed and could result in unintended errors re: accuracy.

    Just my personal opinion. I've actually never changed units (imperial to Metric or vice-versa) mid-course although I have done a drawing displaying alternate units (see Dimension Styles).
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    I tend to not use Imperial units at all, but I switch between using meters and millimeters once in a while. So, I'm adding a caveat to what I am about to say, since it might be different with imperial units.

    Agreed with Remark that it should really not be done, decided on a unit from the start and go with that. If you for some reason need a drawing (the actual drawing, for dimensioning it's different) in two systems, I would have two dwgs.

    That said, if you do change the units, as far as I know, nothing big will happen, as in the stuff that you have drawn will not change. What will change is the measurements of the lines, the dimensioning and ofc when you do a new line, you'll have to enter the lenght differently.

    Note though, that the lines will not scale to fit the new units. As for me, if I first draw in millimeters and then switch to meters, a line drawn as 15mm will now be 15meters.
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    I do the layout of an Agricultural Show, and all the trade stands are in multiples of 10 feet. Apparently, the canvas tents only come in Imperial dimensions. One year, the organisers tried to metricate the stands making a 6m stand instead of 20 foot as previously, and every one noticed. They were complaining about the missing 4 inches.

    So now I draw up the stands in Imperial measurement, but take off the setting out coordinates in metric. To help me swiftly change from one system to the other, I have set up a scaling line, based on 0,0, so I can scale everything by reference. Works a treat.
    Attached Images

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    Looks like accuracy is something to be concerned about when between Imperial and Metric. Very good example.
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  6. #6
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    Inches to Millimeters
    1 25.4
    2 50.8
    3 76.2
    4 101.6
    5 127.0
    6 152.4
    7 177.8
    8 203.2
    9 228.6
    10 254.0
    11 279.4
    12 304.8
    13 330.2
    14 355.6
    15 381.0
    16 406.4
    17 431.8
    18 457.2
    19 482.6
    20 508.0
    21 533.4
    22 558.8
    23 584.2
    24 609.6
    25 635.0
    26 660.4
    27 685.8
    28 711.2
    29 736.6
    30 762.0
    31 787.4
    32 812.8
    33 838.2
    34 863.6
    35 889.0
    36 914.4
    37 939.8
    38 965.2
    39 990.6
    40 1016.0
    41 1041.4
    42 1066.8
    43 1092.2
    44 1117.6
    45 1143.0
    46 1168.4
    47 1193.8
    48 1219.2
    49 1244.6
    50 1270.0

    All the above are correct you should never change units mid job etc, but if you have to, scale away chart above helps as does the cool image posted above by eldon (very smart).

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    How about fractions of inches to millimeters?
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  8. #8
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    Quote Originally Posted by ReMark View Post
    How about fractions of inches to millimeters?
    Maths not my strong point strangely enough ...

    There's a nice Units Converter on the Autodesk website under Services & Support/Units Converter (cannot post link as am new here)

    How about using quickcalc ?

    To convert fractions of an inch to mm

    Using AutoCAD’s QCALC, enter the as a sum dividing the bottom into the top.
    i.e. 3/32” = 3 divided by 32 = 0.09375”
    press enter


    This converts the fraction to a decimal.

    Now go down to Units conversion and complete the from and to values to inch and mm (as required)
    As you complete these to sum is calculated
    2.38125

    Hows that ?

  9. #9
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    Well my point wasn't to have you produce another conversion chart. Sorry if I mislead you. But thank you just the same for the additional information.
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  10. #10
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    Quote Originally Posted by ReMark View Post
    Well my point wasn't to have you produce another conversion chart. Sorry if I mislead you. But thank you just the same for the additional information.
    Your welcome but I haven't my man, its just an example of how to use AutoCAD’s QCALC to do just what you wanted fractions of inches to millimeters.

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