I would like a better understanding of how material is removed when polishing with a pitch lap.
To abbreviate this:
As I understand it, the tool is covered ith pitch and is set on top of the ground a figured mirror with water and CeO, etc.
Once set, a pattern of channels is cut offset making squares so that none line up the same with the center.
As I understand it, this tool has the shape of the mirror at this point.
This is where I expect I am wrong.:
I expect that the pitch is relatively firm but might deform slightly over time. During a single grinding session, I think it would mostly remain fixed in shape.
Since the tool is convex, most of the action will take place at the center as the tool is moved about.
1. If the tool is kept evently pressed, Is there only action occurring up to the point where the center contact?
2. How does a turned down edge occur if the tool only slightly overhangs a blank? I understand you can press offcenter but I do not expect most are when doing polishing initially unless the attempt is to focus in a particular zone. How is the edge getting ground?
3. Is it better to do uneven pressure when working a zone or to move the tool?
Ultimately, I am looking to better understand polishing with pitch and how to determine what strokes to use based on testing results. I undeerstand you can 'only level a hill and cannot fill a hole'.
I have not yet begun my mirror work but would like to understand how to make choices in stroke or tool size before I begin.
I will be using Foucault and Ronchi testing. I would prefer to focus on after determining what the tests indicate but feel free to provide your own pictures if it helps to discuss stroke and tool selection.
To me, this is the black art of telescope making.
With much appreciation,
Frank
__PRESENT
Edited by Fly2High, 15 April 2024 - 02:28 PM.
