polishing with a sub diameter lap

A question

If you have a 13 inch mirror and a 10 inch lap to polish it with what stroke do you use ie is the stroke length 1/3rd of 13 inches? ie would take the 10 inch lap if working on top to just over 2 inches above and below the 13 inch.

Or is the stroke simply just over 2 inches forward and back of the 10 inch tool?


Very interested to see which one applies?

Phil; Mark is correct. I assume you are doing everything as handwork. I did exactly what Mark warned of. I was polishing with a sub diameter lap and I started figuring before I had the blank completely polished out and it did not take very long at all to dig a big hole in the center which I interpereted as a TDE. I went back to grinding and then started again because of my inexperience of understanding the test results. I used the center over center stroke with tool over hang of 1/4 on each side. This gave me a sphere very quickly. I used a machine to polish the blank and I had about 6 hours in to get a full polish and boy was the surface smooth but let me warn you once you start figuring the surface changes fast. Use short sessions and test thoroughly before you do your next session.

Good Luck Dave