Push/Pull a circle from a rectangle


Gday guys just need a little help here. I would search but don’t even know what terms I would search for.

Basically, I want to create a headlight bucket for an RC car I’m going to get 3d printed. The rectangle will be the top (18x22mm) and dropped about 5mm below the rectangle will be an 18mm dia circle, nice and centralized to the rectangle.
Hopefully you can see this from the picture.

Question is, how do I stretch or whatever the term so I have a surface, so it would look kinda like funnel with a rectangular rim and large round outlet?

Joining extruded pipes at an angle
Morphed objects?

While moving the circle SketchUp automatically triangulates the rectangular face.
Eraser+Ctrl soften/smooths the edges.

Notice the orientation of the cardinal circle segments, such that they are parallel to the edges of the rectangle.

Square to circle "adapter"

Geo, I was going to ask "How do you get the transition to be symmetrical? Try as I might, I always get the following: "

But your comment about the cardinal points means I need to rotate the circle so the circle’s edge is parallel to the sqaure’s edge. It’s odd SketchUp does not create a nice symmetrical transition when creating the geometry in the more natural SketchUp way (without rotating the circle.)


Thanks for reply. I think I worked out the first bit, I didn’t have it as a 3d object, nor held the Alt button.
Still not getting expected results. I increased circle segments from 24 to 48, still didn’t get results.


Here is my 1c:

I used the Sandbox from Contours tool:



And after you’ve learned how to do it by hand, you can speed up the process with a plugin like Curviloft (Fredo6)…


Not being a coder, I wouldn’t know if one can program neatness.
Thankfully, there’s a way to encourage it. :grin:

That most, but not all, of the new edges are soft/smooth seems rather odd behaviour too.


Thanks for the help everyone. I downloaded Curviloft as you suggested Cotty, it worked brilliant after playing with the settings.


Then there is the good old hand-stitching method. Note that I used a circle that had 4 times the segments of the corner fillets so the shape could be created without triangulation. Time about 15 minutes.



To have rounded corners at the bottom may seem to make hand-stitching needed.
But the shape is part of a transition from rectangle to circle, the base cut off by an exploded “Create group from slice” via section cut. This reduces the time by maybe 11 minutes, leaving only 4 minutes, still only basic tools, including the use of “Flip Edge” on some edges in an early stage.


Another way to do it - much quicker and doesn’t use any plugins:

1 - draw a circle
2 - split it into quarters and delete 2/3 of it
3 - pull the quadrant up
4 - use the scale tool to select the inside corner of the top quadrant and scale it (eg by 0.1)
5 - draw a vertical line from the outside edges of the bottom quadrant, constrain with the up arrow and click on the small one.
6 - join these with the outside edge of the small one
7 - select all and group
8 - copy and "paste in place"
9 - use the scale tool and select the mid-point on one of the sides
10 - type in “-1” and hit [return]
11 - select both, copy, paste in place and use the scale tool again to make the whole shape.
12 - select all 4 objects and explode
13 - use the eraser with [shift] to soften the joins.

done. (took longer to write than to do)


Sometimes I encourage ‘proper’ auto-folding, Move + Alt, by drawing a few lines between the two parts to be folded. .


I would use Curviloft for this but George’s method can be improved upon.

Given the circle is the default 24-sided thing, divide each edge of the square/rectangle into 6 segments. Weld them together if you wish. Then use Move with Autofold to move the circle. Or move the rectangle with Autofold instead.


< 1m

Hello Dave and thanks for the opportunity to ask a question!! In wrapping my mind around it, in a sense is this to match up with the 6 points of the circle. Almost as if you quartered it (the circle) to match each point with edge points of the square/rectangle? But if you divide and weld it are you not going back to square one…??

Did them both ways and what I see is it eliminated the need to rotate the circle to aline the circles segments to the edge. Removing any doubt or trouble with a clean transition on Auto folding upward.

And you would need to divide the edge in proportion had you changed the circles segments to 48.

EDGE.skp (62.9 KB)


Hello William,

Yes, indeed. As many endpoints on the square as on the circle so if the circle has 48 sides, you would need to double the number of segments used on the rectangle.

And as I think has already been pointed out, even with rounded corners on the rectangle, you’d get the best result with matching numbers of points.