【转帖】ellipses

yang686526

ellipses
what is the proper way to dimension a true ellipse.
wes c.
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when they broke open molecules, they found they were only stuffed with atoms. but when they broke open atoms, they found them stuffed with explosions...
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i usually draw vert & horiz cl's thru the middle of the ellipse, then dim the side arc and the top arc stating "2x" on each dim. use position tol if needed.
chris
systems analyst, i.s.
solidworks/pdmworks 05
autocad 06
i would dimension the two radii, minor axis, major axis and foci distance.  then you just have to locate it and add your favorite gd&t
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heckler
sr. mechanical engineer
sw2005 sp 5.0 & pro/e 2001
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never argue with an idiot. they'll bring you down to their level and beat you with experience every time.
i draw & dimension both axes and clearly call out the fact that it is an ellipse.  seeing as how an ellipse has a precise geometric definition that should be sufficient.  add whatever tolerances and/or gd&t controls you think are necessary.
a true ellipse does not have radii to define it's shape. the only way to accurately define/measure one is to give x-y co-ordinate points.
some nc programs can interpolate the true path required from the major & minor axes lengths, others will need multiple co-ordinates to interploate between.
cbl... that's what i'm looking for, since the radi is constantly changing as you follow the chord of the elipse, what is the "standard" for drafting this....
i usually dim the major axis, and minor axis and i'll call out the degree to which the elipse lies as a reference, but today i was tasked to find the convention, and i can't find it in any of my books...   
wes c.
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when they broke open molecules, they found they were only stuffed with atoms. but when they broke open atoms, they found them stuffed with explosions...
i draw a line to the midpoints of the major radii and also the minor radii, and then dimension the length of the lines.  some cad software, such as solidworks, will not let you dimension the arcs because they are spline entities (which is why i do it this way).
flores