Precision - Changing Angle and Radii

At my company we're encouraged to use the highest precision CAD can muster in our drawings. For some reason, my radii and angles are changing very slightly. You can see in the screenshot below whats happening to radii and the same is happening to angles on parallel lines that I offset. I think this might be happening when I fillet the end of lines or break them or trim them, but I am definitely not using a tool to change the angle or radii, because I've been monitoring it for days now and being careful. Does anyone know if this is a setting or precision issue in CAD? is this just CAD being CAD? Any help would be appreciated. Thanks!

Welcome to CADTutor Pringle.

How is it that a LINE has a radius?

If you think about it, wouldn't offsetting a CURVE change the radius?

It seems to make sense that the radius of an offset curve would differ from the radius of the original, by the CURRENT OFFSET DISTANCE displayed or newly specified at the commandline.

Maybe it wasnt obvious, but I'm not offsetting curves. I'm using whole number radii and they are changing for no obvious reason.

This is happening to angles of seemingly parallel lines as well. I'm offsetting lines and when I first offset the line, the angles are the same, but later on I check back and the angle has changed ever so slightly.

Is it possible to use this high of a precision? Is there a setting I have that is off?

That certainly does sound strange, albeit at a precision which is otherworldly.

The worst case shown in your screenshot is off by less than 1/600,000th of a unit.

Remind me not to borrow a tape measure from your guys in the field.

Don't take that to mean I don't sympathize, I understand the aspiration of perfection.

I am unable to replicate this problem, even with dimension precision set to the maximum 8 decimal places.

So, I would deduce that the level of precision is not the real issue.

I suspect that, as slight as the discrepancies are, that you may be correct and they are being caused by trimming or filleting.

Are your objects a long distance from 0,0

On your images the start X and Y aren't visible, close to the UCS origin everything is usually fine but once you start working at large distances from the UCS origin then things can start getting a little odd.

This was a line drawn with keyboard entry and was exactly 100 units long, then rotated by 45°

the same procedure drawn at the UCS origin behaves without the error.

Are your objects a long distance from 0,0

On your images the start X and Y aren't visible, close to the UCS origin everything is usually fine but once you start working at large distances from the UCS origin then things can start getting a little odd.

This was a line drawn with keyboard entry and was exactly 100 units long, then rotated by 45°

the same procedure drawn at the UCS origin behaves without the error.

+1 steven-g, seems like a very sound hypothesis!

Interesting. Thanks for testing guys. I really appreciate it.

Yes our coordinates are on NAD 83 and I'm working in Michigan.

I realize the precision is kind of insane but AutoCAD should not display that type of precision if its not able to support it?

I"m not sure why you assume we dont have CAD standards.

I did some testing and I can get the angle of a line to change almost every time when I fillet the line to a radii larger than 30.

I trimmed and extended a bunch of offset lines and nothing. I also joined a bunch of lines as polylines and exploded them and nothing.

Is anyone willing to test this on their end?

Testing won't alter anything, I haven't got the faintest clue about mathematics I get lost adding up above 20 (because I run out of fingers and toes) but I do understand that Autocad will show numbers to a precision of up to 8 decimal places but even if you have it set to only show integers, in the background everything is still worked out and registered to 64 bits. If you want some light reading material try http://autodesk.blogs.com/between_the_lines/2004/01/more_on_64bit_p.html or http://core.ecu.edu/ITEC/chinr/59thmidyearproceedings/189.pdf

And many more like it.

Testing won't alter anything, I haven't got the faintest clue about mathematics I get lost adding up above 20 (because I run out of fingers and toes) but I do understand that Autocad will show numbers to a precision of up to 8 decimal places but even if you have it set to only show integers, in the background everything is still worked out and registered to 64 bits. If you want some light reading material try http://autodesk.blogs.com/between_the_lines/2004/01/more_on_64bit_p.html or http://core.ecu.edu/ITEC/chinr/59thmidyearproceedings/189.pdf

And many more like it.

Thanks! This place rocks.