Esteemed reader, I have a question that is perplexing me and I need help. (I am trying to use Blender as a CAD program and I know this isnt a good start) I need to make a torus (hulahoop shape) that is 46 inches in Diameter x 1" thickness with an 1/8" wall thickness. I use the controls for Major/Minor, Exterior/Interior highlighting Exterior/Interior and use the numbers 46.00 x 44.00 and this generates the model. My question however is related to the terms Radius which I understand to mean a radii of the dimensions which should be half that distance, correct? However the Diameter would then be wrong so I assume Blender is meaning that the Radius is actually "Diameter" since the model works that way and not the other. Is this correct? In a hulahoop shape that is 46 inches in outside diameter made of 1 inch extrusion the center dimension would actually be 45.5 inches because the tube is 1 inch thick and the measurement of 45.5 would be passing through the center of the object, hence 45.5 gives us a final dimension of 46" x 1". The reason it is important to me is that I am interested in precise curvature of the 46 inch hoop using 1 inch extrusion and the curve must be exact as well it is applied to other parts that get inserted into it. My question is thus: If I use the figure of 46" is this to the outside of the torus or is it through the center which would be making the curvature off by 1/2"? How could I be sure that the curvature of my extrusion would follow the 45.5" inch centerline through the part? It gets a little more complex for me because I generate another model torus that is thinner by 1/4" and use it to "boolean" the first one and hollow it out so I have a hulahoop that measures 46" x 1" with an 1/8" wall thickness (1/8" on each side is 1/4") I further make another tube with the same radius to insert into the hollowed out hulahoop to create an insert joint that also has a 1/8" wall thickness that is also hollow. So my work flow is like this: create 46x44 torus T1 create 45.8x44.2 torus T2 create 45.6x44.4 torus T3 use Torus T2 to hollow Torus T1 with boolean (subtracting it from T1 giving it an inner wall) use Torus T3 to hollow Torus T2 with boolean to create a connector that slips into T1 but is also hollow with 1/8" wall thickness. Is this the correct or at least a functional way of doing this according to Blenders use of the terms Radius interchangeably with Diameter. (in terms of the curvature being 45.5" center of material) Is there a way to be even more precise down to the thousandths of an inch so as to design in tolerances? Thank you very much for your time and knowledge sharing.
If you set the Dimension Mode to Major/Minor then a 46" Diameter Torus with a with a 1" outer diameter tube would be specified as Major Radius = 23" and Minor Radius = .5":
That is, in answer to your question, using Major/Minor, the Major Radius is the radius of the circle that is aligned with the center of the torus and the Minor Radius is the radius of the circle that is the cross section of the torus.
In the Item display in the side panel, this object will appear as 47" x 47" x 1" because that is the size of the Bounding Box:
It is 47" because the outer diameter of the torus consists of the diameter of the central circle (2 x 23 = 46) + the diameter of the cross section (2 x .5 = 1), since one half of the cross section extends beyond the center in each dimension of x and y. The Z dimension is 1 because that's the diameter of the cross section.