I am a new user of SketchUp. I need to create a cube inside of a sphere where the points of the cube touch the inner surface of the sphere.

I know how to make both a sphere and a cube, but I cannot make them concentric and the correct dimensions.

I am a new user of SketchUp. I need to create a cube inside of a sphere where the points of the cube touch the inner surface of the sphere.

I know how to make both a sphere and a cube, but I cannot make them concentric and the correct dimensions.

Share what youâve got so we can see. If I were doing this sort of thing I would model everything in place centered on the model origin.

Start with a cube and draw the diagonals:

Construct a circle in the plane of the diagonals:

Use the circle to make a sphere:

The radius of the sphere is the sin(60 [deg]) times the length of a side of the cube. For a 10 cm cube, that would be 8.660254 cm.

4 Likes

As a little challenge I did check that via Geogebra on my phone. In SketchUp itâs much easier to do though.

I would probably do it this way, note that I am keeping the circle aligned to the red axis and âguessingâ the touch point. If you snap the circle to the corner of the cube the subsequent sphere created will miss the other corners.

3 Likes

I donât understand. Why would it miss the other corners?

1 Like

Make it into a sphere and see what happens.

1 Like

The very nature of a circle in sketchup makes it miss.

1 Like

I get your point now. I was using 96 segments so there wasnât much of a miss. Hereâs another approach:

1 Like

I think both methods are equally not quite accurate, but close enough.

Your four pies, mmmm pies, wonât match up properly with a circle, close but no cigar.

My method is only as close as you can guess it.

In the grand scheme of things itâs two imperfectly skinned cats that have no skin.

1 Like

scaling is pretty accurate:

Used a line for snapping the cube when scaling about centre.

Afterwards, one can resize the model with the Ă of the sphere or side of the cube

1 Like

This is all very interesting in a theoretical sense, but none of it is much use when it comes to 3d printing. More info is needed from the OP to actually give an appropriate solution, there needs to be thickness somewhere for this to work and some concept of what is air and what is material.

Iâll leave you all to the mathematic gymnastics.

1 Like

Agreeing with that.

That is what Iâve been avoiding with Geogebra. And with the correct method in SketchUp. And some coffee of course!

(*create cube side=10 > midpoint opposite corners > create sphere using midpoint and corner > show radius*)

You made a good point with:

@jimhami42âs method with four arcs on the cross section gets four endpoints on the facetted âsphereâ.

To also get the other four endpoints on that âsphereâ the process of four arcs needs to be repeated for the circular path on the ground, to ensure all eight endpoints on the final spherical surface.

SketchUp doesnât have an entity for spheres, itâs just faces and edges with no radius or Ă. Thus it will always be an approximate. Drawing the circle with a higher number of segments will increase accuracy, though. Rotating the sphere might work, but then it will become more difficult to work with.

Building an UFO isnât rocket science, there is to much that is unknownđ

2 Likes