If you’ve ever 3D printed some sort of circular shape, you will notice the faceted look you get if not enough points are used. A larger radius will require more points than a smaller radius, but how do you determine how many are good enough? The answer is pretty straightforward, but the calculations…

Hi Jim, first of all thank you for your trouble! So in the example you gave those 71 sides for a radius of 1, but what unit is this radius, cms, inches? And the tolerance, how does that relate to radius? Why did you use 0.001 and not 0.1 or 0.000001 for instance?

@jimhami42 would it not be a good idea to keep the cardinal points for circles… e.g. n = (scale * Math::PI / Math.acos((radius - error) / radius)).to_i for i in -6..6 do n = i + n if (i + n).modulo(12).zero? end UI.messagebox("N = " + n.to_s) john

I probably could have made things a little clearer … The tolerance is the amount you’re willing to deviate from the true radius. While the calculations don’t depend on the actual units, the numbers should be meaningful in the units you are using. My example would be suitable if you’re using inch…

I think that’s a good idea, depending on what you’re going to do with the circle. Perhaps it should round up to the next multiple of 12 instead of -/+? I typically will mentally adjust the number I need to make it more readily divisible at the node points. I would note that the cardinal points are h…

I see now! Tolerance in mechanical terms for me is an entirely different thing and I’m sure you know what I’m talking about. Here you use the term for “tolerance to bumpiness” or words to that effect :smile: I don’t have the time right now but I’ll come back to you later, that “e” parameter must ha…

Nailed it! The term for your “e” dimension is the Sagitta, which means Arrow in Latin. I should know this, because “arrow” is the exact term in my native language, and I should have it hammered in to my had for the amount of times I heard in the Boy Scouts: “Your tent is 'orribly floppy again! Now g…

I was thinking it was the “chordal height” or “chord height” or some-such … now I know :smile: Here’s a better diagram for the equation:

I’m a bit dense today…why 12 not 8? Or for that matter, 4?

@slbaumgartner , that’s just me, I use multiples of twelve when doing them manually by eye for some unknown reason… in code I would probably use 4, or more likely ± 2 to make the jump more gradual… john

[image] slbaumgartner: why 12 not 8? Or for that matter, 4? Depending on why you are calculating the number of points to use in the first place will determine whether you want to use the number calculated or modify it to an even number, odd number, multiple of 4, 8, 12, 16, etc. Using 12 al…

How many points for a smooth curve?

SketchUp 3D Printing

jimhami42 January 24, 2020, 6:41pm 20

The picture got deleted in “the purge” … here’s a reasonable facsimile:

There’s a plugin for this … see this thread:

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How many points for a smooth curve?

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