# Why are holes not completly round?

**Hello. I have a really annoying problem. I make wooden cabinets for kitchens and I make holes in the cabinets for wooden dowels. However my CNC machine cannot read the exported file because the holes are not completely round. I you create a hole and zoom in the circle has small edges all the way around.

Yes, this is how Sketchup works.

You may need to increase the number of segments (sides) e.g. to 96 or more when you about to start create a circle. (The default number of sides is 24)

https://help.sketchup.com/en/sketchup/drawing-basic-shapes#draw-circle

Thatâs because SketchUpâs circles and arcs are âsegmentedâ.
As @dezmo suggests increasing the numbers of segments in a circle side step the isue, otherwise exporting the object as a 3d DXF [with suitable settings to avoid âface-perimetersâ etc] should avoid the issue and generate true circles ?

1 Like

Interestingly, Layout for 2D line work does support circular and curved edges.

And these curved geometries are maintained when exporting to DWG/DXF.

yeah, because layout is a 2d drawing software. drawing curves in 2d is easy, a circle is defined by a centre point and a radius, and Ď, or you can use beziers curves like you did.

the issue in 3D is that weâre working with faces and volumes.
so your cylindre of radius 1 has a perimeter of 2Ď meaning the side face (curved one) has a length of 2Ď.

as an equation itâs simple, thatâs why entity info gives you the proper perimeter using maths.
as geometry itâs more problematic, to model with precision using faces, itâs simpler if the faces have rational sides.

many 3d drawing software will do what sketchup does, but they wonât always tell you. theyâll often visually smoothen the circle / cylindre when you zoom in and out so it always looks perfect.
pretty sure that even in autocad you can change the arc resolution so they appear as segmented (faster) or smooth.

In some 3D modelers, there is a distinction between an objectâs representation in the appâs database and its presentation on the computer display. For example, a sphere might be represented by center and radius but presented as a faceted polyhedron. The user can choose the level of detail in the presentation, with a performance impact as it is increased.

SketchUp does not work that way. The only geometric primitives in its database are straight edges and planar polygonal faces. Aside from shader tricks such as softening and smoothing, there is no conversion to a different form for presentation.

A few object types in SketchUp, notably circles and arcs, have attached metadata that preserves their true parameters. But these are consulted only if you change them via entity info, in which case the old polygon is discarded and a new one created for the change, or during 3D dwg export. The metadata is not used while presenting the model on the display.

I suspect SketchUp was designed that way because the conversion from representation to presentation requires much more computation than the âflatâ way that SketchUp works. At the time it was designed, these conversions would have produced much slower performance. Todayâs CPU and GPU hardware is much faster and could probably handle the conversions better so long as the user doesnât demand great presentation detail on complex models. But that would require a total rework of SketchUp, which is not likely to happen.

2 Likes

You might get some ideas from this search from the SketchUp YouTube site.