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Stargazing Network
While getting the machine uncovered was the first chore, getting it cleaned up was the second.  Although the machine would be getting dirty with the grinding grit, we needed to make sure that the grit was just what we put on the tool, not from old dirt falling onto the surface, which could cause serious scratches.
Jim (Mettler) and Jim (Sattler) found that the machine had been last used to grind a 6" mirror.  This required that the stroker cam be adjusted.  It needed to be adjusted so that the upper object would go about 1/3rd of the mirror's diameter past the edge of the lower object.  This is the length of the standard grinding/polishing stroke.
The standard stroke normally requires that the upper object also be moved gradually side to side, about 1/3 the mirror diameter in either direction, so that the center of the upper object traces out a W shaped path over the center of the lower object.  Also both the upper object and the stroke direction are occasionally rotated.  In this case, the machine produces only slight side to side movement, but that is countered by the machine's constant rotation of the lower object and the more frequent  rotation of the upper object.  The upper object is not held firmly in place by the alligator. Instead, it literally bounces between four rubber bumpers.  The looseness allows the object to turn a bit at the end of each stroke.  The relatively crude construction of the alligator also insures that the rotation of the upper object is not too consistent, which could introduce regular errors in the shape of the mirror due to the cyclic nature of the action.  Randomness causes any errors to be distributed around the entire surface of the mirror and average out so a reasonably spherical shape will be formed.
The standard stroke normally requires that the upper object also be moved gradually side to side, about 1/3 the mirror diameter in either direction, so that the center of the upper object traces out a W shaped path over the center of the lower object.  Also both the upper object and the stroke direction are occasionally rotated.  In this case, the machine produces only slight side to side movement, but that is countered by the machine's constant rotation of the lower object and the more frequent  rotation of the upper object.  The upper object is not held firmly in place by the alligator. Instead, it literally bounces between four rubber bumpers.  The looseness allows the object to turn a bit at the end of each stroke.  The relatively crude construction of the alligator also insures that the rotation of the upper object is not too consistent, which could introduce regular errors in the shape of the mirror due to the cyclic nature of the action.  Randomness causes any errors to be distributed around the entire surface of the mirror and average out so a reasonably spherical shape will be formed.
Finally it was time to begin rough grinding...