Dimensioning Ellipses in 2D drawings

[DDoerschuk]

Forum members,

I apologize, I posted this new topic yesterday evening, but due to early brain death I was calling the curves parabolas, not ellipses. Over 30 people read the post, and must have wondered whether I had lost my mind. I had. Fortunately, it seems to be back again, and so I re-post below using the correct word: "ellipse". I'm sorry for wasting your time. David.


I tried using the dimension tool on an elliptical arc (a chunk of an ellipse) in a drawing, and was surprised to find the tool did not seem to do anything. I just assumed that it would give the lengths of the major and minor axes, and maybe some indication of the center point.

These elliptical arcs are particularly hard to dimension because they are not 90 degree segments, in fact, they neither start or stop on their respective major and minor axes: they span a range of 25 to 37 degrees of arc out in the middle of a quadrant.

So, I have two questions if I may:

1. Does Alibre Design have an automated method of attaching dimensions to an ellipse or ellipse arc, and

2. From a draughting point of view, what is the correct way on the drawing to show the dimensions of these small segments of elliptical arc? I was thinking of showing the 90 degree quadrant of arc that contains the drawing arc, perhaps in a dotted line format, and then the major and minor axes and the center point (intersection of axes). Is there a better or standard way to show these arcs?

Thank you very much for the help!
David

 

[wathavy4]

Hi, David.
I might as well confess that I usually screw up the first reply by answering off the point.
So don't expect my reply to save your awes, as usual.
But I guess, I have the same problem as you do.
I could not dimension it. I could see the points there, but I cannot dimension.
If this is persistent to others, perhaps it's B_G. :roll:

Anyway, to have the ellipse at the first place, you have to have it at certain position which are properly dimensioned anyway. So I put artificial dimensions to 2D drawings from the existing sketch dimensions.
I uploaded an example file also. here.

Please have a look.
Cheers.

 

[DDoerschuk]

Hi Toshi,

Thanks very much for your detailed look at the problem! You have shown it exactly: to properly dimension an ellipse the drawing should show the center point, the major and minor axes, the gross rotation, and in the case of an elliptical arc, the start-point-degrees and the stop-point-degrees. On an elliptical arc (like a circular arc) the drawing does not even show a center point. It would be nice not to have the do the dimensioning manually, maybe this is a good suggestion for an enhancement?

Thank you again for your excellent answer!

David

 

[wathavy4]

Hi, David.
You're welcome.

The enhancement request is adequate, I personally agree much with your opinion.
I have never noticed this issue.
Best Regards.