Inventor General Discussion

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*Hoder, Dave
Message 1 of 12 (78 Views)

Offset Ellipse

78 Views, 11 Replies
07-17-2003 01:47 AM
I posted a file to the CF w same subject. I have offset an ellipse & now
want to offset that ellipse, but it's not selectable with the offset tool.
Has anyone else seen this? The workaround (again) is to offset the original
& dim it where I want it but why can I not select the one I want? I also
just found out that when you break the link to a derived sketch, no
constraints are retained.

--
Dave Hoder
Product Design Engineer
idX Seattle
www.idxcorporation.com
*Berry, Patrick
Message 2 of 12 (78 Views)

Re: Offset Ellipse

07-17-2003 02:02 AM in reply to: *Hoder, Dave
A line offset from an ellipse is not an ellipse anymore, it's a splined
curve. RMB on it and select "convert to spline" then you can offset.

Pat

"Dave Hoder" wrote in message
news:6C10899D43E667577E2A2F6D46D11BD3@in.WebX.maYIadrTaRb...
> I posted a file to the CF w same subject. I have offset an ellipse & now
> want to offset that ellipse, but it's not selectable with the offset tool.
> Has anyone else seen this? The workaround (again) is to offset the
original
> & dim it where I want it but why can I not select the one I want? I also
> just found out that when you break the link to a derived sketch, no
> constraints are retained.
>
> --
> Dave Hoder
> Product Design Engineer
> idX Seattle
> www.idxcorporation.com
>
>
*Hoder, Dave
Message 3 of 12 (78 Views)

Re:

07-17-2003 02:08 AM in reply to: *Hoder, Dave
Thanks Pat, where can I find more info on this? More & more customers are
requesting elliptical and organic shaped products. Why isn't an offset
ellipse just a smaller ellipse?

--
Dave Hoder
Product Design Engineer
idX Seattle
www.idxcorporation.com
*Berry, Patrick
Message 4 of 12 (78 Views)

Re:

07-17-2003 02:49 AM in reply to: *Hoder, Dave
See iCF.

Mathematically, an offset of an ellipse cannot be an ellipse. Draw an
ellipse and then draw a second ellipse, centered on the first, with both
major and minor axis increased by the same amount. Now compare this with an
offset from the first ellipse. Notice how the true ellipse is different
between the axis.

I get the same push to design with elliptical section. I try to avoid true
ellipses whenever possible. Instead use an ellipsoid constructed out of 2
pairs of arc sections. You can get this as close to an ellipse as anyone
will require, but the geometry is very simple so the models don't get nearly
as complicated.

Pat

"Dave Hoder" wrote in message
news:C99AD326DF8434935838DAEF8322C000@in.WebX.maYIadrTaRb...
> Thanks Pat, where can I find more info on this? More & more customers are
> requesting elliptical and organic shaped products. Why isn't an offset
> ellipse just a smaller ellipse?
>
> --
> Dave Hoder
> Product Design Engineer
> idX Seattle
> www.idxcorporation.com
>
>
*Fulford, Drew
Message 5 of 12 (78 Views)

Re:

07-17-2003 02:52 AM in reply to: *Hoder, Dave
Inventor actually provides 2 solutions to an ellipse offset scenario.

1. If you pick the parent ellipse at or near a quadrant, the result is an
ellipse.This has no limit on offset-ability but the fact remains that 2
ellipses cannot be considered true equidistant offsets at all distances. To
see this, drag the offset to its minimum (flat) and see that its visually
not a true offset. These results cannot be converted to splines with a RMB
option after creation.

2. If you pick the parent ellipse approximately midway between quadrants
(like north east), the result is a true offset which is not truly elliptical
(will have sharp points). This offset has a minimum limitation where the
offset would become invalid. These can be converted to splines with a RMB
option aftercreation.

- drew

--
Drew Fulford B.A.Sc. Systems Engineer
Solid Caddgroup Inc. Burlington, Ontario
Tel: (905)331-9670, Toll Free: 1-(866) 698-2831, Fax: (905)331-7280
Corporate: http://www.solidcadcam.com/

Member of the Autodesk Discussion Forum Moderator Program
Visit my MCAD website @ http://www.mymcad.com/
"Dave Hoder" wrote in message
news:C99AD326DF8434935838DAEF8322C000@in.WebX.maYIadrTaRb...
> Thanks Pat, where can I find more info on this? More & more customers are
> requesting elliptical and organic shaped products. Why isn't an offset
> ellipse just a smaller ellipse?
>
> --
> Dave Hoder
> Product Design Engineer
> idX Seattle
> www.idxcorporation.com
>
>
*Berry, Patrick
Message 6 of 12 (78 Views)

Re:

07-17-2003 02:58 AM in reply to: *Hoder, Dave
Thanks Drew, I didn't know about picking near a quadrant. Good tip.

Pat

"Drew Fulford" wrote in message
news:smileyvery-happy:11F452C0736DB6D14388C91A6419EC0@in.WebX.maYIadrTaRb...
> Inventor actually provides 2 solutions to an ellipse offset scenario.
>
> 1. If you pick the parent ellipse at or near a quadrant, the result is an
> ellipse.
*Hoder, Dave
Message 7 of 12 (78 Views)

Re:

07-17-2003 03:07 AM in reply to: *Hoder, Dave
Thanks Drew. Think I should check the Help File first before I ask?:smileyhappy:
By the way, haven't seen your name in the IVP fiasco. Too much of a
political hot potato?

--
Dave Hoder
Product Design Engineer
idX Seattle
www.idxcorporation.com
*Keller, Kent
Message 8 of 12 (78 Views)

Re:

07-17-2003 03:27 AM in reply to: *Hoder, Dave
Patrick

You get the honors of being the third one to lock me up because the file wasn't zipped.
8^)

I have downloaded it from the web and posted it back to customer files as a Zip file.

--
Kent
Assistant Moderator
Autodesk Discussion Forum Moderator Program


"Patrick Berry" wrote in message
news:10B4826759167ADDAE0C5102681BBAA1@in.WebX.maYIadrTaRb...
> Thanks Drew, I didn't know about picking near a quadrant. Good tip.
>
*Berry, Patrick
Message 9 of 12 (78 Views)

Re:

07-17-2003 03:28 AM in reply to: *Hoder, Dave
Sorry Kent. It was so small (<200k) I didn't think it would cause a
problem.

Pat

"Kent Keller" wrote in message
news:3CD188E0FA703F0CFB77FCC9D92FA21E@in.WebX.maYIadrTaRb...
> Patrick
>
> You get the honors of being the third one to lock me up because the file
wasn't zipped.
> 8^)
>
> I have downloaded it from the web and posted it back to customer files as
a Zip file.
>
> --
> Kent
> Assistant Moderator
> Autodesk Discussion Forum Moderator Program
>
>
> "Patrick Berry" wrote in message
> news:10B4826759167ADDAE0C5102681BBAA1@in.WebX.maYIadrTaRb...
> > Thanks Drew, I didn't know about picking near a quadrant. Good tip.
> >
>
>
*Gwin, Hal
Message 10 of 12 (78 Views)

Re:

07-17-2003 04:12 AM in reply to: *Hoder, Dave
Dave Hoder wrote:
> Thanks Pat, where can I find more info on this? More & more customers are
> requesting elliptical and organic shaped products. Why isn't an offset
> ellipse just a smaller ellipse?
>

Check out the thread, Offset Eliptical Conundrum, posted 7/12, in the R6
NG. Loren Jahraus provides a good technical explanation of the offset
ellipse issue.

--
Hal Gwin
Mechanical Designer
Xenogen

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