8" Telescope Mirror Parabolizing: Done??
I did a tiny bit more parabolizing, then re-measured my mirror. Last time, my spreadsheet and measurements told me my outer zone needed to focus tiny bit farther and my lower zone needed to be a tiny bit closer. To dig the inner zone out, I did some W strokes with lots of mirror movement on the tool edge, and then used long center over center strokes with a tiny offset to dig everywhere but a tiny strip of outside. For parabolizing, you imagine the edge of your moving circle does the cutting, so stroking back and forth one inch off center (while rotating around the mirror!) will dig everywhere except an area around one inch into the mirror. Compared to last time I only did a tiny bit of polishing: just three times around the circular table.
My mirror looks so close to perfect. Each zone is focusing light to within 0.006" of where it should. My goal was to turn a sphere into a parabola; I may have been a touch hasty and dug a slightly too deep hole and made an “overcorrected” mirror shape. But… wow. That’s pretty much perfect! I might be done!