Defining an ellipse

[panfield]

Hi All

 

I use all my knowledge of technical drawing from school many years ago to produce drawings in AutoCAD 2002, but I can't remember how you would define the dimensions of an ellipse in a drawing so that someone could produce it from the plotted output.

 

Any thoughts.

 

Mike

[architecture68-raff]

An ellipse is defined by a major and a minor axis. That's the way they are usually dimensioned. Is this what you are looking for?

[panfield]

Thanks for the reply.

 

I realise from AutoCAD help that an elipse is defined by the major and minor axis. But if you are given this and nothing else in a drawing could you reproduce the elipse accurately?

 

Mike

[architecture68-raff]

I'm pretty confused as to what you're asking....

 

If you know the major and minor axis dimensions of the ellipse, then to recreate it in autocad use the ._ellipse command and define its center and two axis.

 

If you are asking how to find the dimensions of an already-drawn elispse in autocad, you could select the elipse and have a peek at its properties. Or if you wanted to put actual dimension strings on it, start use the "Quadrant" osnap to snap to the ends of the axis.

[SEANT]

I assume the plotted output is scaled down from the actual part. CNC notwithstanding, the best way to produce the object would be to provide the focal points.

 

This can be determined in Autocad by creating lines for the Major and Minor axis. Draw a circle at the center to the end of the Major axis (i.e., a circle with a diameter the same as the major axis. Now move the circle's center to the end of the minor axis. Where the circle now intersects the Major axis are the focal points.

 

If a person in the shop were to connect a string - the length of the Major axis - to nails at these focal points axis, a pencil could be constrained by the string and generate the Ellipse.

FocalPoints.dwg

[SEANT]

Sorry, here's a ACAD 2000 file.

FocalPoints2000.dwg

[panfield]

Thanks for the feedback. It has helped. But just to make things clearer what I am trying to get cut is a piece of ellipitical glass 800x500mm. Now these guys don't use any sort of software and only work from a scaled drawing. What I'm trying to do is give them all the information required to produce the correct ellipse.

[Guest Alan Cullen]

Draw your major axis, then divide it into a convenient number of parts and draw lines square to the major axis at each of these parts. Dimension these parts and give an offset at each of them to the elipse........

 

[ATTACH]1051[/ATTACH]

[SEANT]

Glass rules out nails I guess.

 

The size you require could be printed out 1:1 on a wide format printer, if one were available. If not, maybe you could generate 25 mm offsets for the Major axis and list the perpendicular distance. Interpolating from point to point should create a pretty accurate ellipse.

 

It looks like I'm a few minutes too late.

[panfield]

Thanks for all your help guys.

 

I'm off to the glass shop!!

[Prophecy99]

Just wanted to say this is the best thread for Ellipse Dimensioning & Defining. I read all the others, this one had the most info & attachments.

Thanks Cadtutor & SEANT

[SEANT]

Hey, that's cool to hear.