Doubt about drawing Circles - AutoCAD vs SketchUp

Hi everybody.

I’d like to know if AutoCAD works in a different way for drawing circles than SketchUP does.

Circles in Sketchup are made by segments, 24 it’s the default value, I know I can change that.

I run into the following problem, let’s suposse I have all info for drawing two tangent circles, that means:

  • I know where both centers are placed.
  • I know the radius for both circles

The problem is they usually don’t really touch each other, so I cannot delete the part of the circle from the tangent point, because tangent point doesn’t exist.

So far what I’ve been done it’s to draw arcs to make sure they touch each other, but they don’t have the very exact radius they should have, it’s not a real problem to me, but I’d like to know the following things:

  • AutoCAD works in a different way?
  • Is there any workaround different than the one I’m doing?

Thanks in advance.

to draw a true tangent, rotate the circle (made as group) so a vertex point is at the required position, draw a line between vertex points either side, then move the line to the correct point. If required another tangent, then draw an arc with same radius at center from this point to other, then copy rotate the line, then change the circle segments to suit

Hi @spawn ,
Check this plugin: TrueTangents .

I don’t know the differences or logics behind Autocad and SketchUp, so i can’t compare really. But i think it’s just because SketchUp wasn’t designed to be ‘mathematically correct’. %99 of the time increasing segment count suits our needs.
Also take a look at this topic .

Thank you guys.
I use TrueTangents, it tells you where the true tangent points are but they don’t touch the circle because is made by segments, I guess pcmoor recommendation should work but I usually try to make the reference line parallel to some of the axis.

You’ve been using SketchUp long enough now to have figured this out. You know that SketchUp represents circles with polygons. The radius of the circle can only be measured to a vertex on the edge and you need a vertex on each circle positioned at the tangent point if they are to meet. If you are going to use SketchUp for these things you’re drawing, you need to come to terms with that.

I showed you weeks ago how to sort out getting a vertex at a tangent point. You could do the same in this case.

Yeah, it wasn’t my intention to offend the software capabilities nor doubt about your previous answers, I don’t need exact drawings so far, but I’d like to know what things are a limitations and which ones are not.

I’m happy with SketchUP, and of course I remember your demonstration using TrueTangents and connecting the lines from the intersection points.

If someone would ask you if it’s possible to draw something in sketchup with exact measurements, what would your answer? does it depends on the drawing or all kind of drawing it’d be possible?

I would say it depends on what it is you are drawing and to what precision it needs to be drawn. It also depends upon how the drawing will be used after it is created. IT is possible to make drawings in SketchUp at higher resolution than normal people can measure.

Recently there was a guy trying to draw parts for 3D printing and wanted to set precision to more than 6 places right of the decimal for millimeters. Despite the fact that that his 3D printer couldn’t come anywhere close to that kind of precision not could he measure the part to that precision once he’d printed it, he decided SketchUp wasn’t precise enough for his purposes.

You need to have realistic expectations. SketchUp will be more that precise enough for the sorts of things you’ll be making. Time to quit worrying about that and just get on with drawing.


Wise words as usual :slight_smile:

AutoCad, btw, displays circles as polygons, too, but treats them geometrically as true circles. From the Autodesk knowledgebase:

As SketchUp is a polygon modeling application, the segment count of an arc or circle determines the face count of the 3D shape created by push-pulling it.

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