Sketch DXF export - arcs vs. polylines

[kristofpucejdl]

Hello,

I am often using Fusion to create files for laser cutting. I have recently experienced a weird issue when exporting sketches to DXF. Some arcs export as arcs or as polylines, solely based on the surrounding geometries or even constraints, even though in fusion sketch, they are identical. Here is an example. First sketch is this:

Fully constrained, contains four arc, manually drawn and constrained (dimensions, coincidences and  horizontal/vertical alignments of points, tangencies of arcs). This sketch exports as the attached file 'arc.dxf'. In the file, clearly, there are four arcs and no polyline.

Now I connect the two loose points to complete the 'slot'. Nothing changes about the dimensions of the preexisting arcs.

This updated sketch now exports as polyline and just one arc that represents the construction line in the middle, see the 'polyline.dxf' attached. And this is not the only instance when this ambiguity occurres for me. The same happens for instance when I project a face onto a coplanar sketch. The edge of the face only consists of straight line and arc segments, however, the projected sketch exports as a polyline in dxf. Meanwhile when I project the individual segments of the edge of that face (manually click on all of them instead of on the face), it exports as lines and arcs. Why is this happening? Is there any way to avoid this? By the way I would swear I used the same workflow before and I didn't have this problem, arcs always remained arcs and only different curves converted to polylines. This feels to me like a recent change of the behavior.

Thanks for any explanation or hint!

[HughesTooling]

I suspect the problem is the software you're opening the DXF with. Have you tried opening the polyline file with Fusion, I get all the arcs using insertDXF.

Also works fine with Rhino3d.

I suspect the problem is your program can not read polycurves and is ignoring them. You might be able to use another program like QCad or NonoCAD (both free) to explode the polycurve.

[kristofpucejdl]

Hi Mark @HughesTooling 

Thanks for having a look, and you are right about that some software can handle the polylines better and even re-interpret them as arcs, but that does not change the fact that in the fusion exported DXF code, the geometry is simply represented differently, despite being identical in the sketch. I am using some old version of AI with the laser cutter and it simply imports polylines what they are - a segmented line. And for larger diameters that means very poor approximation of the arc. Maybe there are workarounds, but I would rather know whether there is a way to avoid this arc-to-polyline export thing in fusion. 

[laughingcreek]

so it seems like it's happening on closed profiles? is that correct?

are you exporting from the file menu or from a right-click on the sketch?

[HughesTooling]

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@kristofpucejdl wrote:

Hi Mark @HughesTooling 

 is a way to avoid this arc-to-polyline export thing in fusion. 

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This is not a Fusion problem. The 4 arcs are joined into a closed polycurve, they are still arcs. There was a change in Fusion to export profiles as joined polylines or polycurves but this was done about 6 or 8 years ago. If you are getting segmentation in AI it's because AI is doing the segmenting not anything to do with Fusion and Fusion has no export options so you'll need to use another program to explode the polycurve or update AI.

[HughesTooling · Accepted solution]

It looks like if you create a 2d drawing then export the drawing as a DXF you get unjoined curves. The attached DXF is an export from the 2d drawing workspace, I hid the border and title block so only the outline of the part is in the drawing.

[kristofpucejdl]

..I replied here to different comment, sorry.

[MichaelT_123]

Hi Mr KristofPucejdl,

Consider exporting the sketch with the show profiles options turned off.

Some time ago, while facing "some programming" challenges, I have had to convert a closed path into a closed spline/closed polyline.

It would be worth... checking.

Regards

MichaelT 

[kristofpucejdl]

Hey Michael, interesting thought, was worth checking. But it made no difference on the exported file.

[kristofpucejdl]

Thanks, I replicated your result and this works! And thanks for clarification/explanation. Since I am unable to change the AI based workflow for the time being, this will be an applicable workaround.

[kristofpucejdl]

Hello, it seems like the polyline conversion does not happen to open ended
curves, but I do have examples of closed profiles that export acrs as
proper arcs as well. Now that I am thinking about it, though, the other
profiles may have contained straight line segments and not been
continuously tangent like this one… so maybe that can make a difference?
And yes, I export from the dropdown menu, save as DXF.