OK, so imagine a ball end mill, 2 inch radius. (I know that's pretty big, but bear along with me a moment.)

So if I plunge this spherical cutter into a piece of material, say .750 deep, I get a circular depression. The diameter of the edge is 3.1225". Simple enough.

Now if I were to take this same cutter and allow it to swing on a 4 inch radius, coming down into the material, swinging down to the same .750 depth, and continuing to swing it around, back up and out of the material, I get an oval looking depression in the stock, with a short axis and a long axis, 3.1225" X 4.6637".

My question is: Is this a true ellipse? Or is it something else? If it is not an ellipse, how do I draw it?

So if I plunge this spherical cutter into a piece of material, say .750 deep, I get a circular depression. The diameter of the edge is 3.1225". Simple enough.

Now if I were to take this same cutter and allow it to swing on a 4 inch radius, coming down into the material, swinging down to the same .750 depth, and continuing to swing it around, back up and out of the material, I get an oval looking depression in the stock, with a short axis and a long axis, 3.1225" X 4.6637".

My question is: Is this a true ellipse? Or is it something else? If it is not an ellipse, how do I draw it?

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