With so many people doing CNC projects and 3d printing these days, the need for true arcs & circles, instead of line segments, has never been more needed. That begs this user community to either motivate Trimble to add this functionality, or to move to a different paid tool (abandoning Sketchup most likely).
Thoughts, folks?
Adding NURBS support to SketchUp would, according to what has been said by the developers over the years, requite SketchUp to be rewritten from the ground up. So it is not likely to happen in the near future. Some more expensive and less intuitive competitors do support several kinds of 3D geometry (faces, NURBS, quads) in a single application.
never because SketchUp is a polygon modeler.
If you need analytic geometric entitites, use a CAD system.
I’m 3d printing a lot, never missed true arcs.
Not what you are asking, but have you tried increasing the sides?
When we need more accurate arcs or circles we increase the sides and seems to do the job fine, still not perfect arcs but works for us.
Also haven’t had issues 3d printing.
Someone, (was it @slbaumgartner ?) produced a nifty calculator to calculate the ideal number of arc segments for a given printer layer thickness/resolution. Overdoing it just, again, makes SketchUp slower without showing in print quality.
Not me. Maybe @jimhami42 ?
The fun part is that Nurbs get tessellated when ported to gcode or slicer software eventually, it kind of looks like the neverending discussion of light rays, partikels or waves?
In real world, we can describe mathematical arcs, but we can never touch or create them.
As I move Sketchup DXF files to Vectric Vcarve (for CNC cutting) lines and arcs seldom meet and require a fair amount of cleanup both on circles & arcs as well as simple arc-to-line transitions. I find I often have to do some redesign after the export->import process.
Use 3D dxf export instead of 2D.
If you are just outputting toolpaths of a CNC table in 2D you can output true curves. I do it all the time. Set the camera to PP, set the view to TOP, export 3D, choose dwg, in the options set the checkboxes to export only edges, export. The resulting file will be a 2D dwg with true curves.
Search the forum, I’m on my phone now but we have discussed this many times here and you should be able to find detailed instructions.
Ik believe if a segment is not longer than 1mm it should be nearly invisible in a 3d print.
Ik never had problems with printing…
Like @tweenulzen I used to use a ballpark method of making the segment length fixed and approx. equal to the nozzle diameter. But also suspecting that was a little overkill. It does makes a difference tho if you are making round shafts that rotate in bushings and you want them to rotate smoothly without oversize clearance. Also 3d printed threads and nuts. For example, threaded bolts and nuts, they can be 8mm diameter for bolts, and 80mm diameter for jar lids.
But now, I’ve just installed jimhami’s above mentioned extension. I can see now that the segment length must vary with the diameter of the part. By jimhami’s reckoning, I come up with 0.6 segment length for 8mm diameter part and 2mm segment length for 80 mm diameter part.
So I think this will work just fine, just have to try printing some parts now.
Ik also think this is overkill, but it can also cause problems while printing!
Every segment is a change in direction for a specified length. So every segment is a few lines in the G-code and that means the more segments, the longer the G-code.
A long G-code an sich is not a problem unless that code had to be executed in a very short time!
Older printers can hiccup on such a code (pauze every second or so) or it could mess up the whole print…
There is simply to much information to be transfered in to little time.
The only wat to tell if it works is to test it!
Every print requires specific values for specific settings.
One of the things that makes 3D printing fun and an adventure!!
I understand that in all 3D printing the STL format is used to transfer a model to the actual slicing software that creates the layers and paths for the printer. STL consists of triangulated flat faces, so the facetting will happen anyway.
I have done both CNC and 3D printing and have never had a problem with SketchUp and arcs and circles. It is a matter of proper modeling to begin with. You can control the number of line segments to a point where the human eye cannot tell there is a line segment so what is the point of complaining about it 
It all starts with the first line you draw. Go back to basics
