[ATM] Thinking while parabolizing

[jonathan_bishop at sbcglobal.net (Jonathan Bishop)]

I am currently parabolizing an 8" F5 mirror and it got me to thinking about what it means to parabolize. Basically until the point where I decided to parabolize the objective was to get and stay as close to a sphere as possible.

This happenned naturally because the sphere is the only surface which stays in contact at all orientations and positions. Now that I am parabolizing this will no longer be true.

I am using a long wide W stroke with mirror on top (the classic approach according to Texereau) and now I am noticing that the mirror does not quite glide over the pitch lap as it used to. It feels like it get a little "stuck" as it passes over the middle.

Is it possible that the mirror is no longer being spherical is the cause of this? How does a lap polish a mirror which is not spherical. Is there enough "flow" in the lap to conform to the mirror as it passes over it?

Of course there is the possibility that I did not do enough warm pressing so the lap and mirror are not in full contact. When I do warm pressing though I feel like the drag between the mirror and lap is really tremendous. In fact I need to push really hard to get the mirror to move! Probably something is wrong there also.

I would be happy hear any advice on this.

Thanks,

Jon Bishop