Ellipses not recognized by CNC machine

Hi. Absolute novice here. I tried to learn to make ellipses as oval sinks to be cut on granite, marble, etc. I finally learned how to do ellipses, however, my cnc cutter does not want to cut. Sent to factory, they said 100s of arcs in ellipse,and open links, simplify , I was told. Well, don't know how to simplify or another way of creating an ellipse in DXF. Everything looks good on a CAD but by machine's CAM will not accept it. Can anyone shine a light on this, please? Thank you.

hm... actually, that's quite a wide question, as different CNCs may support a different set of commands.
In some cases, a complex shapes (like ellipses, splines, arcs etc) should be interporlated - either by lines, or by arcs (where possible).

Right now LibreCAD does not include a tool to interpolate the ellipse via lines, however.

However (yet I'm not sure) - if they mentioned arc, probably they refer to the elliptic arc?

If it is so, you may try to replace the single ellipse by one or two elliptic arcs (they are supported by LibreCAD) - and probably that will help.  

Welcome huchipila!

Basically CNC's don't like complex curves, because the calculation of X/Y coordinates along the curve, in an acceptable resolution, is too expensive in the sense of computing time.
A circle or circular arc is much cheaper to compute using sine/cosine tables. An ellipse has different radii in each point of its circumference, that's probably what the shop meant.

You can try a simple trick and save the drawing in R12 format. On file save find the format drop down and select R12.
DXF R12 has no ELLIPSE entities and on save it is converted by libdxfrw into a bunch of small straight line segments.
As I have some expertise in stone machining, this method might be not sufficient, because the line segments are not tangent. It possibly works when the cutout is ground/polished by hand afterwards.  

Some post processors do the conversion on the fly by creating an approximation with circular arcs. The advantage with circular arcs is, that the result has a G¹ Geometric Continuity like the ellipse.
An approximation for a quarter of the ellipse is sufficient and can be applied to the other quadrants too. A good approximation with acceptable deviation starts with 4 or 5 circular arcs per quarter. More arcs can reduce the deviation but also makes it more complex.

This avoids any angles because the contour is tangent overall, and it works fine for stone machining.
Sadly I don't know any simple method to draw this approximation by hand, with a reasonable level of deviation.

Armin