Having trouble joining curves

I got re-inspired to learn more about sketchup techniques after watching the live u-tube q&a tutorials this week. (BTW - I learned a lot!) My current issue is that a circle joined with another circle will not act as a single entity. Rather than explaining how I tried to get this to happen (and i’d be happy to if you are interested), I would rather ask how you as experts would do it.
Here is the example I found online to try to model:
I thought I was mostly successful with this:

but many parts of the outline are separate entities and I want them to be a single object.
If you look closely, I’ve selected one segment.
Specifically, it was the R7 radius that I was trying to duplicate that caused the issue. When I zoomed way in, I could see that they were really close, but did not touch, even though I typed exact measurements rather than relying on dragging close to the intersection (especially since it’s a circle and there are 2 intersections). I tried aligning the circles along an axis and increasing the number of splines in the circles, but no luck.

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Looking at the model you are trying to copy, it seems that all radii are true arcs that resolve with each other. If so, all you need are the foci positions of the radiuses and the radius dimensions themselves. You would be over-complicating it by introducing splines.

It would also makes sense to divide the drawing up into at least quarters, maybe even eighths, as there is pattern repeat there.

For the benefit of others who can use extensions, Weld would join arcs together.

You are right, the R7 is difficult to achieve. I’ve added a circle that can be moved accordingly, but it’s difficult with an arc directly, maybe @DaveR has another idea for the construction of that radius? Or does @TIG s True Tangents plugin can help in this situation?


Should work ok as long as you don’t have too many segments.


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You could calculate the right number of sides to use for the circles such that the R7 arc could be drawn tangent to each AND end on vertices on both circles. I thought about doing that but since my coffee is still brewing, I decided that was too much work.

The easy way would be to add the circles shown in cyan. Their intersection is very close to the center of that fillet. And you’d be pretty close. I used 96 sided circles because that was already set from a previous model.

To get something in between too much work and the easy route, I used True Intersections from TIG’s True Tangents to find out where the center of the R7 arc should really be and where it would intersect the circles. (I erased a bunch of guides that weren’t needed for the job.)

You can see that the easy method comes out pretty close. The point marked by the guidepoint is from the extension. For references, an average human hair is 0.06 to 0.08 mm in diameter so the difference is about 1/10 the diameter of a human hair. Smaller than most people could measure.

I think in practice I would take the easy route. The nice thing about TIG’s extension is it also shows where the ends of the arcs need to be.

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Thank you, DaveR and others! I’m impressed by your quick and helpful replies.
The method you mentioned of drawing the other 2 circles and using their intersection as the centerpoint was the one I had tried, but I guess because of the circles being made of straight segments, there was no true intersection unless I got lucky and the rotation caused 2 of the circle segments to be right where I needed them.

I haven’t used any extensions yet, but I’m eager to try.

Thanks again, and stay safe out there, or in there!

If you increase the number of sides on the circles as I did, you can get the intersection to be very close as I showed. Probably no real need for any extensions.