Master B9 builder Marc Chabot, however, brought to the world's attention the interesting fact that, in the original robot costume, this ring was not vertical but was canted, or tapered inward at a slight angle — perhaps around 80 degrees. This tapering is very difficult to verify in still photographs and in screen grabs, but it is there.

One can see the tapering of the inner ring in rare scenes of Lost in Space in which the robot tilts his head toward the camera. The  taper of the top ring is very easy to see in the enigmatic third-season episode Castles in Space (episode 73, production number 1513; original airdate:  20 December 1967).

While the taper is admittedly difficult to verify in most photographs and screengrabs of original robot costume, it is immediately apparent even in the low-resolution scan of a photograph of the stunt robot's radar section.  Respected Lost in Space robot authority Brian Mix took these photograph many years ago. The photo was taken at Greg Jein's storage facility. Jein is theHollywood prop builder who owned the stunt robot and other robot materials at the time the photographs were taken.
 

(jpeg gratefully borrowed from Michael Davis' excellent Robot Information Website)

A slightly sharper taper is also easy to verify in this photograph taken of the original hero robot's radar after it was restored by Hollywood prop builder Greg Jein. This photograph is a closeup that I downloaded from Paul Monroe's fantastic Lost in Space Anthology. Anyone with even the slightest interest in Lost in Space or the Robot should order a copy of this invaluable resource. The photo was taken the day the Greg Jein's restoration was presented at the Northeast Collectibles Extravaganza held in Boston in December of 1990.

I am convinced that this is the original radar rather than a new fabrication of Greg Jein's because the radar was incorporated in the monstrous mutilation of the robot for the dreadful Hanna-Barbera children's series Mystery Island in 1979. The following photograph conclusively proving this point is also from the Lost in Space Anthology.

Notice that the spinner posts were discarded. Greg Jein had to create new ones. It is very sad to think that Twentieth Century Fox could have sanctioned this willful violation and destruction of Robert Kinoshita's masterpiece.

What does all this mean? It means that I have decided to correct Dave Painter's Robot Blueprints on this point.  My machinist has given a gentle taper to the inner ring of my robot's aluminum radar.