Difficulty creating globes

mac
#1

I have been trying to create spheres or parts of spheres but there always seems to be missing facets or other extraneous matter. To create a hemisphere (for example) I start with a circle. I give it a good number of segments (say, 50). I then draw a quadrant at right angles to the circle with its base centred on the circle. Then I select the circle and use Follow Me on the quadrant.

I may be trying to do this at too small a scale. Most recently I tried to create the head of a dome headed nut with a diameter of 20mm. If that causes problem, a workaround might be to model it very much larger and then scale it down. But should that be necessary?

Here’s a typical result without scaling:

Am I doing anything wrong?

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#2

Generally that sort of result is due to working at too small a scale. Use the “Dave Method”.

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#3

I generally do, Dave, but not sure what it is in this instance! Presumably, drawing large and scaling down? I still get a few anomalies but they are easier to deal with, admittedly. Do you have a failsafe method?

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#4

The "“Dave Method”…

SketchUp cannot create edges less than 1/1000" long and you’ll get these near to the top of a tiny dome with many facets.
I suggest you draw the path circle and profile face at the size required and make it a component.
Then copy that to one side and Scale the copy x1000.
Edit the giant copy.
Do the FollowMe and the now larger faces with be created.
Exit the edit and delete the giant copy.
The original tiny copy will show the new faces.
Tiny geometry can exist, but it cannot be created.

Also I recommend that you give your circles/arcs a segment count that is divisible by 4 [and preferably also 3] - so 24, 36, 48, 72, 96 etc…

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#5

TIG described the “failsafe method” and a quick search will turn up several animated GIFs from Box demonstrating it.

I’m typing on my phone and it’s a pain to post the link.

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#6

Thanks @DaveR and @TIG. I knew there would be a workaround if I asked!

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#7

Just FYI this is a particular problem with spheres because of the way “longitude” lines converge at the pole. It causes narrow slices whose edges often run afoul of SketchUp’s small edge limit.

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closed #8

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