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Ellipse length
Deepak Gupta Jan 23, 2008 6:51 AM (in response to 16TXHTM)Hi Lorne,
Are you trying get the flat pattern of the elipse.. 
Ellipse length
Kelvin Lamport Jan 23, 2008 12:38 PM (in response to 16TXHTM)Given the perimeter and size of one axis, you could use a DT to calculate the other axis.
http://www.efunda.com/math/areas/EllipseGen.cfm 
Ellipse length
Pedro Nunes Jan 23, 2008 1:19 PM (in response to 16TXHTM)yeah kelvin, you are right... but i try to use that formula and the result becomes with ~10% of error, wich i think in cad/cam is a very bad approximation
Ellipse length
16TXHTM Jan 23, 2008 3:13 PM (in response to Pedro Nunes)What I am looking for is to be able to call up the length in a cutlist or BOM and to be able to drive the shape of the ellipse based on length (like the dimension around arc function). We have a number of different head sizes but the bottom sheet is always the same length (84"). Right now I have to model the ellispe, dimension the X and Y axises and then trim the partial ellispe to length by trial and error and dimension the end points (which change if the head size changes). What I would like is to be able to dimension the axises and the length of the partial ellipse.
I hope that made sense. I don't need a flat pattern for this application.


Ellipse length
Roland Schwarz Jan 24, 2008 6:42 PM (in response to 16TXHTM)Believe it or not, modern mathematics has not come up with a way to calculate the exact perimeter of an ellipse or partial ellipse. Any formulae you find are approximate.
Ellipse length
16TXHTM Jan 24, 2008 6:51 PM (in response to Roland Schwarz)I guess my frustration with this is that I can measure the length of a partial ellipse (aproximate as it may be) but I can't drive the length with a dimension.
Lorne


Ellipse length
Mahir Abrahim Jan 24, 2008 9:31 PM (in response to 16TXHTM)If you try Google, many other more exact approximations can be found.
Ellipse length
16TXHTM Jan 30, 2008 3:15 PM (in response to Mahir Abrahim)Just an update. I have figured out a work around that seems to work for my application.
What I did was first sketch a full ellipse to the dimensions I want.
Second I added arcs to the bottom of the ellipse (where I needed the partial ellipse) I added references of coincident of both end points of the arcs to the ellipse and created a point at the midpoint of each arc. I also added a reference from this point to be coincident to the ellipse.
I then added length dimensions to the arcs (all of them adding up to the value I need), and sketched a line that crossed the ellipse and was coincident with the two outermost points of the arcs.
I then trimed the ellipse with this line making a partial ellipse with a driveable length (it won't be 100% accurate but close enough for my application), and a driveable ellipse size.
Lorne
Ellipse length
1GU3IT0 Jan 30, 2008 3:51 PM (in response to 16TXHTM)Would this work for you ? see pic
elipse length.JPG 56.0 KB

Ellipse length
16TXHTM Jan 30, 2008 4:07 PM (in response to 1GU3IT0)I have posted a couple of screen shots to show what I am doing.
The one picture shows the sketch of the partial ellipse that I need to drive the length of (the sheet is 84")
The other picture shows the top and bottom welded together.
The whole issue with this is that I can drive the elliptical shape but not the length of the partial ellipse. My work around does accomplish the length issue but is cumbersome.
Lorne
ellipse2.JPG 84.9 KB

Tank Shell.JPG 104.4 KB



