NX6: Basic Dual Dimensions Not Correct Between Inches and Millimeters

[gruenhir]

Hello,

On one of our drawings, it seems that all the dual dimensions are off. By 'off' I mean that the inches would be correct, but the mm would not. For the ones that were set up as 'limit', we were able to correct the issue by changing the +/- values on the mm. However with the 'basic' dimensions, we are unsure why the mm would not convert correctly from inches. Again we're in NX6, so the options to resolve this for newer versions do not seem to be available.

Thanks!

 

[cowski]

For the dimensions with tolerance, make sure the drafting preference "convert tolerance when changing units" is turned on. It has been a while, but I'm fairly sure that this option exists in NX 6. For the basic dimensions, how far off were the values? You might need to increase the number of displayed decimal places for the secondary dimension.

www.nxjournaling.com

 

[jerry1423]

It is also possible that one of the two dimensions was added as appended text.

Jerry J.
UGV5-NX11

 

[gruenhir]

Cowski -- Thank you for the recommendation. I checked Preference > Drafting, but none of the four tabs (Edit: tabs named 'General', 'Preview', 'View' and 'Annotation') had any option like 'convert tolerance...' As for the dimensions, they ARE very close, however when I increase the displayed decimals, it does not resolve the issue. For example, one of them is 3.480" / 88.40mm, and increasing the visible decimals makes it 88.405mm. I would have expected to see 88.392mm. Another is 2.554" / 64.86mm (or, 64.863mm) when I would've expected to see 64.87mm or 64.872mm.

Jerry -- Since the displayed text of the in and mm dimensions does change when I play with the visible decimals, and the text box contains nothing unexpected, I'm not sure that it's an appended text issue, though that's a good suggestion!

 

[ewh]

Is your inch dimension rounded? 64.863mm = 2.55366 inches (which rounds to 2.554). If the dimension is 2.5440000 then I would expect NX to return a mm dimension of 64.8716.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[gruenhir]

ewh -- That would be the issue, I think! It's 2.553671 in / 64.86324 mm.

 

[looslib]

A couple of things to take into account that could be causing this.
1) The rounding or truncating of the inch dimension and/or the metric conversion.
2) Rounding rules where a value is rounded to an even number to 'average' out the rounding.
3) If dealing with tolerances, the conversion should always be within the original dimensions. For a limit dimension, the converted displayed values should be numbers between the original numbers after rounding. This way if using the converted numbers, the part can never fail inspection outside the original values.
4) Converted dimensions in a dual dimensioned drawing are usually considered reference dimensions.

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[ewh]

looslib is correct in that converted dimensions should be considered reference, otherwise the drawing would ultimately define two different parts.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV