ellipse segment radius

[tails]

In the attached image there is an ellipse broken into segments. How do I work out the radius of each segment as when I split up the ellipse the radius tool does not work. Tracing over it with an arc is not accurate.

 

Any ideas?

[JD Mather]

Tracing over it with an arc is not accurate.

 

Doesn't the definition of Radius involve a (circular) arc?

What are you going to do with this number that you are after?

Are you familiar with the ellipse mathematical formula?

 

Also, equidistant offset of an ellipse is not an ellipse.

[eldon]

I always thought that an ellipse has a constantly varying radius, which is given by the appropriate equation.

 

I think there is no exact solution to your problem.

[tails]

Yeah, I understand that an ellipse does not have a radius.

 

Basically its going to be a bar for a show I'm designing. It was going to be CNC'd but now they want it built in house.

 

Each segment holds a particular food section. I need to provide some measurements to build it from and to be honest I'm stumped.

[eldon]

Perhaps you will have to make do with an arc which approximates the ellipse shape.

 

Unless you can feed an equation into the CNC device.

[eldon]

Or plot it out to natural size and make a template.

[rkent]

Look up on the internet, ellipse with string, use that to dimension where the pins will go, they can draw it there in the shop.

[Quik&Easy]

I've provided a sample ellipse for you in the attached file. Its 96" long x 48" wide and the inner is another ellipse (not an offset) 80 x 32, giving an 8" wide surface. The center of the circle is the center point of the ellipse for reference.

 

Does this layout help?

 

This is drawn on a white background, by the way. I guess I do things backward from most everybody else.

forum ellipse.dwg

[JD Mather]

.... now they want it built in house.

 

What is your manufacturing tolerance?

I think arc approximations will be well within your manufacturing tolerance.

 

I like the two center foci with string idea - as long as the differences in the two ellipse is not too noticeable.

[tails]

Hi guys, So I'm still working on this project. In the attached image are some nodes where I have divided the ellipse. The vertical line at the top "should" go through the 2 offset lines but it doesn't. Why would it not?

 

I've drawn the ellipse once and offset it and another time using the same method as quick&easy describes. I can't figure out why it would not work.

[JD Mather]

Did you attach the correct image file?

All I see is a circle and a vertical line?

[tails]

I've deleted the ellipse but left the nodes. I can see them but they are faint

[Quik&Easy]

When I zoomed in on the picture the nodes became clearer. If my sample helped you at all, give me the dimensions of your outer ellipse and the dimensions of your inner ellipse and I'll plot them out for you to work with.

[eldon]

I think that you should start at the beginning, and itemise each step that you are taking, and what you want the end result to be.

 

Your first picture does not seem to give the same information as your second picture (can you alter the appearance of nodes in DraftSight), and I cannot see what offset lines the vertical line should be going through.

[rkent]

I approximated an ellipse using 4 arcs per quadrant. I divided the quadrant as shown so the arcs will follow the ellipse closely. Using the arc command start at the top, then move to the left using the nearest osnap to the approximate center of the first arc (12 o'clock to 10 o'clock), start the arc command and hit enter, pick the next endpoint, this will create an arc tangent to the first arc. Do that for the next two arcs. Pedit to combine them, etc. Now you can place dims for the arcs to locate center lines and, of course, the radii.

ellipse with arcs.dwg

[tails]

Hi, okay so rkent's solution might work, I'll have a play later. The ellipse is 10000mm east to west and 6000mm north to south it's then offset 800mm to the inside of the first ellipse and broken into 16 segment. If I can follow rkent's instruction I can make an arc in 4 segments.

[Quik&Easy]

Please forgive the crudeness of my drawing but here it is; I hope it helps you a bit somehow. It was originally drawn in MM in another program but got converted when I opened it up here to attach. I'm a novice so I don't know how to get it to the proper units easily for you. It was drawn at 10,000mm e/w and 6,000mm n/s.

forum ovals MM.dwg

[tails]

Hi, Thanks I'll see if it works for me.

[steven-g]

Do a search for 'ellipse jig' there are loads of videos out there, I've done similar things in the past (large circular bars) with a router fixed onto a long 'stick' 25m was the biggest I think