Segments of a circle or arc


#1

I have an issue drawing small circles with only 24 segments. I need to how perfectly round circles/arcs even at a small size lets say 2" radius… Even large circles. I really need perfectly round continuous curves. Not tiny segments. When you click on entity info, and increase the segments …its a guessing game as to how many segments to add, why not just have a perfect round option??


#2

Quite simply, you can’t have “perfect round” because the geometric primitives that SketchUp manipulates are edges and faces. Inside SketchUp, under the hood, there are no arcs, and hence no circles.

You can approximate by increasing the number of segments, but at some combination of higher segment counts/smaller radii you come up against another limitation of SketchUp: How it determines if edges share an endpoint. Once the distance between end points become too small, SketchUp can’t determine if they are intended to be coincident - with unpredictable results. This can be overcome using the “Dave Method”:

Why? In almost all use cases, especially at smaller radii, a suitably segmented approximation of a circle is indistinguishable from a true circular arc.


#3

“Why? In almost all use cases, especially at smaller radii, a suitably segmented approximation of a circle is indistinguishable from a true circular arc.”

I have run into issues, exporting segmented arcs into Draft Sight to be used on our CNC machine. In order to cut perfectly smooth arcs/radii one smooth continuous arc is required.


#4

Provided the arc/circle hasn’t been edited in a way that causes SketchUp to abandon its circle metadata, a 3D dwg/dxf export will preserve true arcs and circles. Unfortunately, it isn’t always possible to follow that “provided” :frowning:

Edit: But also, DraftSight appears to be an entirely 2D CAD application? In SketchUp 2D exports are always effectively images showing exactly what is on the view, including the segmentation of circles.


#5

are you using the Draft Sight G-Code Generator to convert from dxf or are you simply using it’s dxf output?

john


#6

We draw our jigs as per customer specs using Sketchup, then I save my work with “Camera-Parallel Projection” and then export “3D model” as an AutoCad DXF file. When we open the file in Draft sight, it doesn’t recognize segmented arcs as true smooth curves…This causes problems running segmented arcs as apposed to smooth curves on our CNC. …maybe I’m just missing something


#7

See this link: Exporting 2d faces for CNC


#8

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