True arcs (no facets) in 3D?

Diving into the world of 3D CNC carving, and would like to make some convex shapes (such as hemi- spheres) and concave shapes (as in bowls).
Can anyone tell me if SU is capable of non-facet-ed (true arcs) outputs to a 3rd party program (like Vcarve), and what types of tricks I should know to make this happen? Below are orig SU model, and CNC toolpath maker import…



By now you should know that SketchUp always approximates circles and arcs with short, straight line segments. You can make curves and curved surfaces look smoother by increasing the number of segments you use.

In this model I made the circles, arcs and curved surfaces look smooth but they are still faceted. No way around that.


I was hoping there was something analogous to how true arcs are achieved in 2D with exporting savvy…
As in this post:

3D exports of 2D is different than 3D geometry.

Still, you should be able to manage pretty smooth geometry. You should certainly be able to mange this sort of thing.

96 segments?

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You must be bored. :slight_smile:


If you are having issues with intersections between arcs and other surfaces then you need to get an extension like TrueTangents - draw the arcs/lines that are intended to intersect, use TrueTangents to obtain guide points for the geometric intersection, then re-draw arcs/lines to meet at the guide point.

If you are trying to intersect curved surfaces then you will probably have to manually complete the line of intersection, and then manually fix any microscopic holes along the edge… and to do that, you may need to scale-up the object several 100% to make those repairs and then shrink it to the required size. You can have a lot of fun with curves in Sketchup :rofl:

As @DaveR showed you can get a much smoother surface by increasing the number of segments [and thereby facets] is the arcs/circles you use…
Your example used 24 segments - the default, which often sufficient in general modeling.
However, BEFORE you create a 3d form with faces linked to the curves, which will effectively hard-bake the segment/facet count - you can either increase the curves’ segmentation as you draw those paths or edit a selected curve afterwards by using Entity Info, so that they then have more segments…
In @DaveR’s example he used 96s…

I believe I found a solution to the segmentation issue for those hoping to CNC true 3D arcs…
There is a Smooth Components feature in Vcarve 3D/Aspire, under the modeling tab, which I set to “maximum” and applied to my Sketchup made bowl…

Here is the result:

What Box said is the best approach. You could have a bowl made from a 6 segment circle, and the export to DXF as 3D, and make sure to turn off faces, will give you infinite segment true arcs.

I edited that, I meant faces. Having them on superimposes segments on top of the true arcs.

Thanks John.

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I did not see a comment from Box, so you are the first person I am hearing this from…

I tried this export method (no faces DXF) and still got the segmentation after importing (below).

Was definitely worth a try though.


The Box comment was in the screen shot that Randyl posted.

It could be that follow me stops things from being true arcs.

That’s a good possibility about follow-me tool…
I’m happy I found the work- around inside of Vcarve, thanks to this group/ having people to bounce ideas off of…

Thanks again!

NURBS can exactly describe curves mathematically, but they’re still represented as polygon meshes. To my knowledge, 3D printers can only read polygon meshes too. Your best bet is probably going super high poly to get a smooth mesh, as was already mentioned. But I figured I’d bring up NURBS.

Quick question: Is the ability to change the number of segments on circles in SketchUp similar to NURBS? While SketchUp isn’t a NURBS program, you can increase segments after drawing circles which seems like a mathematical circle.

if you’re looking for analytic NURBS surfaces/solids and an export of them to e.g. the STEP or SAT format, check the stuff from PunchCAD (an IMSI company)… but be aware of a steeper learning curve.

I guess you mean slicer programs…
3D printers van only Read gcode.