What circumstances makes one of these arcs gets segmented?

spawn2k99 2017-09-12 08:33:37 UTC #1

Hi everybody.

Just to know, what makes the last arc gets segmented and not the other ones?

PS: if someone has seen me draw this shape before it’s because I’m redoing some exercises to keep some process clear in mind before I try advanced things.

This is the file if it was necessary: question.skp (12.1 KB)

Thanks in advance.

TIG 2017-09-12 10:39:52 UTC #2

I repeated your steps using your SKP.
I see the issue too.
I works fine for me if I make the radius slightly bigger, or scale everything x10 and down after filleting.
The internal angle fillets then form as arcs without exploding.

I suspect it’s because the exploding arc’s segments are getting very tiny, although redoing them with guides works.
I guess you are just at a tipping point.
The exploded arc is in fewer segments than the normal arc - looks like the start/end segments merge with their neighbors ?

spawn2k99 2017-09-12 11:02:03 UTC #3

Yep, thank you for testing it.

It’s good to know that a possible workaround is working in a bigger scale. (I know Dave method but in this case I didn’t thought it has to do with the small size of the model), however in this case I think the fastest way is to redo with guidelines as you said.

I didn’t try to figure out why it happens, but doing some tests as you did I got this statements:

For this value it affects to both sides (as I expected)

ex1

All arcs that didn’t got segmented are composed by 12 segments (I’m working with circles of 48s)

ex2

If I explode one arc and then I compare the segments with the segmented arc this is the difference

ex3

I counted the number of segments, for the bottom one there are 10 segments instead of 12.

Taking in account what you said that it doesn’t happen with another dimensions for the arc It could be what you suggested and it has to do with the start/end segments and the way they merge with the beighbors, but no idea.

Anyway, it’s not a big deal, just curious.

slbaumgartner 2017-09-12 11:29:54 UTC #4

I suspect @TIG is on the money. One of the lesser known consequences of SketchUp 's small edge tolerance is that an arc can “capture” a nearby edge and merge it. This has been discussed and demonstrated before on this forum (on my phone now so adding a link is beyond my ability).

spawn2k99 2017-09-12 11:47:03 UTC #5

No problem, I thank you answer

eneroth3 2017-09-12 14:03:59 UTC #6

This was a quite interesting read. I suppose the small difference in angle between the two last arcs is is just enough to make one behave normally and one have just a little too short segments for that, with the same radius and segment count on both.

MikeWayzovski 2017-09-12 18:27:35 UTC #7

you can skip the part were the line is drawn, the double click with the arc tool active works for outer and inner corners

Just to know if there is a faster way

spawn2k99 2017-09-12 18:33:29 UTC #8

Wow, I was trying doing double click outside the shape that’s why I thought it wasn’t possible xDD
Thank you Mike, it’s really helpful.

By the way, this is the final result (it’s not a real model, just an exercise) after using follow me tool.

Solido13_skp

robertjuch 2017-09-12 19:07:08 UTC #9

Very efficient workflow, I have always struggled with making arc’s!
last week I tried to write post about this, but did not find how to describe this problem and this post solved my problems