Arcs created as individual segments

I would like to know why in some instances, when I draw an arc, the arc that is created can be picked by a single mouse click and in other instances, the arc requires that I select each segment individually? There seems to be no pattern to when one result occurs instead of the other. The one possible exception is when I delete a segmented-type arch and connect the two points by a new arc, the arc can be selected with one click. I normally create my arcs for fillet type corners, but do not use any special tools to do it, just pick the two points and double-click which completes the arc and deletes the former sharp corner.

Please help!

If the edges are very small, sometimes the arc gets exploded.

There are various manipulations that can have the consequence of breaking an arc apart into individual segments. To make it back into a single entity, use a weld extension. You can find examples on both the Extension Warehouse and sketchUcation plugin store if you search for weld.

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Thanks for your reply.

Is there a way to anticipate when this might occur AND does the setting the segments 12, 24, 100, etc. have an impact on whether the arc will be exploded?

Thanks for your help. I will try a weld extension.

To be on the safe side, you should work at a bigger scale.

Do you mean draw it oversized then scale it down? These are technical drawings and I am using the output for CNC cutting equipment.

I am developing a Ruby script that flattens a steel bent plate and considers the thickness of the steel plate and bending radius to get proper developed length. While testing the script, the segmented arc issue developed.

Yes, it’s an common technique to to circumvent problems with small geometries in SketchUp.

Yes. SketchUp has an internal tolerance of about 0.001". When an operation generates two or more vertices that are closer together than this, SketchUp concludes that they were meant to be the same and differ only due to imprecise computer arithmetic. So, it “cleans up” the model by merging them and eliminating any faces they bordered. Gaps and holes in surfaces result. To avoid this, you must temporarily increase the size of your model (or the affected parts), do the critical operation, and then shrink it back down to the real size. Shrinking does not trigger cleanup, so this workaround successfully avoids the threshold.

Edit: there are also situations in which the tolerance causes SketchUp to decide that a new edge that passes close to an existing vertex was meant to go through that vertex, even though both ends of the new edge are far away from the vertex. It will break the new edge and warp it over to the existing vertex. This can even happen when a new edge passes close to a vertex of an arc while on its way to an adjacent vertex of the arc. The former “steals” the edge.

Thanks very much for your very detailed comments. I will continue to experiment as we are regular users of SU for our technical CNC work here. As long as we understand the limitations, we will know what to watch out for.

One thing to note, it’s helpful if you can keep them from exploding because if you Export as 3d any SU Arcs, Circles etc will be exported as true curves rather than segments.

Thanks to everyone for your replies. I think I have a basic understanding of the difference between arcs and curves - which was causing most of my confusion.