I am trying to draw a sphere. I start with an x-y-z axis or origin point. Create a circle of 6” with 200 segments on the blue axis. I have had the same issue if I do a whole, half, quarter or eighth of a circle in a follow me along a partial circle on the red axis. See the attached file. It appears that it wants to create a thickness as I start the follow-me along the arc which you can see in the final model and it creates a gap in the spherical model.
BGB_20_Black_Cash_Drawer copy.skp (420.0 KB)
It’s invisible!
I don’t know how you’re not pulling your hair out with a 6” 200 segmented circle on iPad…. Mine is so unbelievably slow with that amount of tiny faces going. O.o
Edit: is it a tiny face issue?
I’m not getting any of the tiny top gap with a 6’ circle with 200s… but still the back corner gap. I would think that was the way I set up the path though.
I see your thickness. It’s taking the first face and kicking that back corner out off the axis by the width of one segment. Then your nice 90 degree corner is no more. It’s easier to see with less sides. Got to be something to do with the way the path is set up?
Looks like a misunderstanding of the use of Follow Me. The key thing with Follow Me is that the profile needs to be perpendicular to the first segment in the path and the extrusion will end perpendicular to the last segment in the path. If the profile isn’t placed perpendicular to the first segment in the path, the profile is projected (not rotated) to perpendicular.
With the way you are setting up the profile and the path, the profile is not perpendicular to the first segment in the path so you get the result you are seeing.
You are also running into the tiny face issue at the top due to the excessive number of segments in your arcs.
Here with the default 12 sides for the arcs you can more easily see this. The guie lines are parallel to the axes. The end segments of the path are not.
And after Follow Me, You can see that the ends of the extrusion are perpendicular to the end segments of the path.
Two solutions for this:
One would be to extrude the profile all the way around a circle and then cut out the eighth sphere.
Another method which I tend to prefer is to draw a circle for the path and rotate it so that there are sides perpendicular to the profile start and the desired end of the extrusion. Divide the circle at the midpoints of those sides.
Erase the unneeded part.
And then run Follow Me.
To make the fact that the profile gets projected to perpendicular, I reduce the number of segments in the arc path to 8. Still used a 6 in. radius to start with.
As for the 200 sides on your arcs, for the small size of the object you are modeling, that’s likely to cause you problems. Better to use fewer. Also I find that using a multiple of 12 sides is easier to work with in most cases because it’s divisible by 2, 3, 4, and 6. 96 sides is usually the maximum I will use and for something as small as this thing, 48 sides is probably plenty.
I also noticed you have given a tag to geometry in your model. That’s not good practice. Leave all edges and faces untagged and give tags only to groups and components.
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The path it a quarter circle….
Understood. That’s what I was using, but it didn’t matter because Dave has your answer. Perpendicular path. 
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The easiest way I found to create a partial sphere (half, quarter, eight, whatever) is to create a full sphere and delete unwanted parts.
Here’s an animated version of what Dave was describing about rotating the circle so the start and finish segments are perpendicular to the desired shape.
In this case I have used the same face to create the path and profile, this will give you just the outer skin, a couple of edges will fill the shape if that is needed.
Separating the path and profile will make a filled shape, Just deleting the straight edge of the path quadrant will make a filled shape…
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Sharing a concept (entirely ‘movie-magic’) that I worked on a little while back, for scenarios like this, that I think are too difficult & nuanced to accomplish in SU today.
Curious whether you all have any thoughts about it…
The beginning of the workflow starts by selecting a single edge, which SU interprets as an axis about which Follow-me would then spin/lathe the profile.
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That almost feels like a totally new tool that kind of overlaps with another tool‘s function. That could be ‘lathe ’ and users could choose that or follow me the same way that we choose between rotate and move or push/pull and move. I know I’m not as good as the more practiced users, but the concept of ‘lathe’ makes more sense to me than the follow me for circles. One of these days I’ll get it.
Actually the more tutorials I follow the more I realize how many different ways there are to do things in this program.
Edit; not a necessary tool, but one that might make follow me more user friendly for beginners?
Revolve makes me wanna sweep, too!
I had to change browsers to see your video for some reason.
What you are showing there can be done with Tig’s Extrude tools, specifically Extrude Edges By Lathe.
One can also revolve a profile with Profile Builder3. Tig’s Extrude tools is superior to PB3.