Problems filleting 3D objects

[SDSS]

I am having problems adding fillets to rendered machine parts. I have tried many thing, but nothing seems to work. The programme will not let me add fillets to a 3D object (illegal object warning appears). I have also tried cuting fillets off a simple 2D rectangle, extruding them, and adding them, using add solid command, to the 3D object (cannot preform 3D operation on objects which contain zero volume warning appears). In frustration I tried starting again from simple 2D shapes. The object, from front view, looks like a rectangle with a circle on top of it intersecting the rectagle. I drew he circle and the rectangle, combined them into one object and tried to fillet where the circle meets the rectangle so the whole object would look like a rectangle with a bump on top of it (objects are not consecutive warning appears). Can anyone tell me how to add a fillet to a 3D object????

[Marc Pitman]

If you are trying to cut a fillet or round the corner of a solid this works: 1.) Fillet a 2-d shape, a rectangle, and extrude that shape to a length that will be great enough for a later subtraction from the 3-d shape. 2.) Create another 2-d shape that overlaps the filleted extrusion just created(the filletted corner of the extrusion). Extrude this shape the same as that in step one. 3.) Perform a model/subtract solids on the two extrusions you just created subtracting 1 from 2. 4.) Finally, use model/subtract solids and subtract the result of step 3 from the original 3-d object.

I have found at least one other way to cut fillets but this method worked the best for me. Please, if someone knows a better way let us know.