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leeminardi
en respuesta a: Anonymous

@Anonymous When you say "...for me the big issue was relying on the 4 decimals displayed ..." I think you are missing the point. Most of the problems that you are having is due to poor technique not examining distances.   As noted by @j.palmeL29YX , it is much better to use align than to rotate an object to make two planes flush.   The precision of an angle is a function of how big the reference geometry is and where it is located.   All coordinates in AutoCAD are stored as double precision floating point numbers as noted by @Alfred.NESWADBA .  Essentially this means that all coordinates carry 15 to 17 significant figures.  15 significant figures is a safe value to work with. 15 significant figures does not mean 15 decimal places.  The number of decimal places of precision varies with the distance the vertex is from 0,0,0 WCS. 

To simplify the concept of significant figures let's assume we had a CAD system with 3 significant figures.  A real floating point number is of the form 1.23 x 10^4  = 12300. Here, 1.23 is the mantissa and 4 is the exponent. The next number after 1.23 x 10^4 for our system with 3 significant figures is 1.24 x 10^4 = 12400 a difference of 100!  As we go further away from 0,0,0 the step from one coordinate to the next becomes larger and conversely, as we go closer to 0,0,0 the step becomes much smaller.  For example, 1.23 x 10^-3 = 0.00123 and the next coordinate is 0.00001 away. 

Now think about drawing a line at an angle. Both ends of the line are limited to the precision of the database, 15 significant figures for AutoCAD, 3 for our simple CAD system. Let's say we have a line from 0,0 to 4.12, 3.56 in our simple CAD system. The angle of that line is atan(3.56/4.12) = 40.82956...°  Now we would like to make a line at a slightly larger angle but with the same y coordinate. That line would have its end at 4.11,3.56 forming an angle of 40.89845...°  a difference of 0.06889...°.  Using a longer line would enable making more precise angle rotations.  The angle you cite of 269.9999xxxx is extremely precise and a couple of orders of magnitude better than you could fabricate.  If you build a box orthogonal to the world then rotate is slightly you can get similar errors but they are usually well within requirements.  Note that 3ds Max has a single precision database of 7 significant figures.  This is usually not a problem because the  primary output is renderings or animation.  Not CNC machining instructions. 

 

When using align it is best to use points as far apart as possible.  For your model I would use the align command and the 3 sets of vertices as noted below to get the best alignment. 

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lee.minardi