Does anybody already have a sketch setup to to generate a 4 arc ellipse from a the major and minor diameter?

If you do, could you post it?

Does anybody already have a sketch setup to to generate a 4 arc ellipse from a the major and minor diameter?

If you do, could you post it?

Hello,

You could start with a regular ellipse and add offset geometry trimmed to the ellipse (coradials are added):

Then use Split Entities to break apart the ellipse (coradials are added now) (I added this command to my sketch CM tab):

Things remain elliptical, but you may need to adjust your offset dim too:

Kevin

Kevin Chandler wrote:

Hello,

You could start with a regular ellipse and add offset geometry trimmed to the ellipse (coradials are added):

Then use Split Entities to break apart the ellipse (coradials are added now) (I added this command to my sketch CM tab):

Things remain elliptical, but you may need to adjust your offset dim too:

Kevin

Just so I can understand, what are you trying to show here? The goal is an approximated ellipse that's actually four true arcs. I gather that the purpose is for manufacturability because it's easier to machine arcs than surfaces of continuously changing curvature. However, here you're just breaking a true ellipse into 4 separate sketch segments that remain ellipses, right?

Josh Brady wrote:

Kevin Chandler wrote:

Hello,

You could start with a regular ellipse and add offset geometry trimmed to the ellipse (coradials are added):

Then use Split Entities to break apart the ellipse (coradials are added now) (I added this command to my sketch CM tab):

Things remain elliptical, but you may need to adjust your offset dim too:

Kevin

Just so I can understand, what are you trying to show here? The goal is an approximated ellipse that's actually four true arcs. I gather that the purpose is for manufacturability because it's easier to machine arcs than surfaces of continuously changing curvature. However, here you're just breaking a true ellipse into 4 separate sketch segments that remain ellipses, right?

It appears that I did misinterpret the OP. I read more ellipse than arc. Two different trig entities, though, so at what sizes and at what error level is acceptable?

Kevin

The issue is an older plasma machine. Can only feed it arcs, no spirals.

Have to use the old 4 arcs approximation of an ellipse.

I found plenty of "how to" instruction on how to set this up. Tried to follow a few for an hour, failed, ran out of time.

Figured it was worth asking of other have already set up the sketch to do exactly what I needed.

Turn the major and Minor Diameter into a 4 arc ellipse.

Attache is the how to, that I failed to accomplish in the given time.

Jep S: How to Draw an Ellipse by Four-Center Method

https://cadsetterout.com/autocad-tutorials/converting-ellipses-to-arcs/

S. Leacox wrote:

The issue is an older plasma machine. Can only feed it arcs, no spirals.

Have to use the old 4 arcs approximation of an ellipse.

I found plenty of "how to" instruction on how to set this up. Tried to follow a few for an hour, failed, ran out of time.

Figured it was worth asking of other have already set up the sketch to do exactly what I needed.

Turn the major and Minor Diameter into a 4 arc ellipse.

Attache is the how to, that I failed to accomplish in the given time.

Jep S: How to Draw an Ellipse by Four-Center Method

https://cadsetterout.com/autocad-tutorials/converting-ellipses-to-arcs/

The instructions I posted above achieve the geometry you're looking for, except it's easier because you make SW constraints do some of the work for you instead of having to measure distances.

Hello,

Trim an ellipse to a quadrant:

Use the sketch segment tool to break the quadrant into lines (by selecting "segments"):

The segments are still ellipses, but perhaps your machine won't choke on these if you crank up the number of segments.

Mirror sketch entities twice for a complete ellipse.

BTW: The segmented ellipse saved as a DXF becomes one ellipse again in the DXF.

Kevin

Kevin Chandler wrote:

Hello,

Trim an ellipse to a quadrant:

Use the sketch segment tool to break the quadrant into lines (by selecting "segments"):

The segments are still ellipses, but perhaps your machine won't choke on these if you crank up the number of segments.

Mirror sketch entities twice for a complete ellipse.

BTW: The segmented ellipse saved as a DXF becomes one ellipse again in the DXF.

Kevin

I don't know how this is supposed to help? The machine cannot recognize that entity type, no matter what its length is.

"I don't understand Russian at all."

"OK, let me feed you the Russian sentence one letter at a time. Maybe that will help."

I don't know if it is possible, but if the machine recognizes end points of segment (whether they be arcs, splines, whatever), then if you segment it enough times, then have the machine just jump from endpoint to endpoint, it would look like an ellipse, even though it is tiny little straight lines.

I once had a guy that I was hiring to do some laser cutting do something similar with one of my CAD models.

If you create your true ellipse in draftsight and then save out DXF AutoCad R12 or older it converts it to radius. True ellipse were not supported at R12 and previous so were converted to polylines which come out as multiple radius if I remember correctly

There are other ways in AutoCad but as I don't use draftsight often I don't know if they have the same function but the above should work fine if draftsight follows the correct protocol for R12 DXF.

Richard Gergely wrote:

If you create your true ellipse in draftsight and then save out DXF AutoCad R12 or older it converts it to radius. True ellipse were not supported at R12 and previous so were converted to polylines which come out as multiple radius if I remember correctly

There are other ways in AutoCad but as I don't use draftsight often I don't know if they have the same function but the above should work fine if draftsight follows the correct protocol for R12 DXF.

Richard Gergely is correct.

My segmented ellipse above is converted to a pline, but for some reason, there's a gap at the upper left.

The pline explodes to lines.

Do you mean something like this?