The making of 30 in telescope - 9, shaping finished

夸克星 註冊時間: 2003-10-09 文章: 2207

Dear ATMs,

Since we have been using very eccentric tangential stroke for fast deepening of mirror center during the rough grinding stage, the surface of the mirror departed greatly from a spherical shape. The center of the mirror has a shorter radius of curvature than that of the edge zone. It takes the shaping procedure to resume the mirror surface back to a perfect sphere.

What we have not prepared for is the tremendous amount of time and labor spend on shaping the mirror surface. We have consumed a total of 14 working hours, using extra 10 lbs of #40 grits, to grind the mirror back into a sphere.

The classical method of judging whether the mirror has reached spherical shape is by judging the sir-bubble at mirror center- during grinding a big circular air bubble trapped at mirror center indicates non-spherical surface. However for extremely large mirror this method may cause misinterpretation. A better way is to use a spherometer – when the reading at mirror center and edge zone is exactly the same, the surface must then be a perfect sphere.

So far so good. We are preparing for a fast fine grinding of mirror next week hoping that polishing of mirror will be commenced not later than next next Monday.

Best regards
Chan Yuk Lun
9-4-2005