Sphere size defined by three faces

[Daox]

I had a drafter come to me today asking if there was an easy way to do this... so here goes. He basically wants make the red sphere inside this part to be as big as possible. He didn't say the application or reason. Anyway, I've been going over this for a while now and figured I'd throw this out there.

Rename the .zip to .sldprt for the part file.

[clembrant]

I would do a save as, then cut the part in half, get rid of one half and then draw a tangent circle, then half the circle and revolve. Don't merge results, get rid of what you don't want

[Daox]

That would make this quite easy. However, it won't work. You have to compensate for the rib (and lack of rib) since the sphere will protrude into it somewhat. See the picture for an example.

[DareBee]

I would basically do the same as clembrant accept I wouldn't have cut it in half, just use a plane through the centerpoint.

If all you need is the ball AND are starting from scratch, I would draw the cannel/groove and the tangent circle (in cross-section) and just extrude the sphere by itself.

[DareBee]

Originally Posted by Daox That would make this quite easy. However, it won't work. You have to compensate for the rib (and lack of rib) since the sphere will protrude into it somewhat. See the picture for an example.

HUH

I am confused
Make it tangent to the area that it is to fit into.

BTW I was typing out my last post while you were posting this.

[Daox]

In the picture above you can see the sphere protrudes outside of the part on the right side in back of the rib (and top, but it was a quick example). The sphere must remain inside the part.

[DareBee]

Make it tangent to internal edges then.

[Daox]

Again, that will not work if I am interpreting what you are saying correctly. That leaves a gap where the sphere could be larger than what it is. The problem is that you can not draw a 2d sketch and define it correctly because the constraints are not planar.

[DareBee]

Can you define a plane (thru line and point) that slices thru the needed geometry and sketch on it?

3D sketch a line between your lower 2 tangent areas and make a point in the center of the rib fillet (you may need to make some "split lines" here).
This will give an askew plane to sketch on.

[Daox]

There is no way of defining a plane to draw my sketch on that I know of, even when using a 3D sketch. I did try that yesterday. The sphere must be tangent to the inner conical face, and the four corner fillets of the rib (see picture). How would you define that in a 3D sketch? I guess the title of the thread should have been sphere size defined by 5 faces really.

[DareBee]

There is likely some way to do it creating lots of sketches, the advantage of doing this is that the sphere size will always be relative if the other geometry is changed.

When you figure it out, let us know

I would likely do a workaround to get the job onto the floor.
Insert the disc thingy into an assembly.
Model a sphere that will be close the right size and insert it into the assembly.
Mate it to the 4 fillets.
Measure the gap to the cone and add this number to the dia of the sphere (you may need to create a sketch to measure this).
Not very parametric, but it gets the job done in most cases.

[clembrant]

try not slicing it through the rib.