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On a Sunday afternoon, Tom W and I poured a new pitch lap onto an 11 3/4″ disk.Image

Worked on the mirror with center-over-center strokes for about 40 minutes. (Good attendance at the workshop today with up to seven people at some point.) Test on TW’s rig showed what I’ve seen for a while now: a high center with turned edges. (Ronchi test outside radius of curvature shows a “watermelon” pattern, though the lines should be curved the other way.) A new idea for next time: to hot-press the tool with a piece of paper that has a hole in the middle, so that the middle of the blank gets more work than the edges.

12.5" mirror blank with a 10" tool on top

Worked on the mirror with center-over-center strokes for 45 minutes (mainly while talking to EdK about bicycling, which made the time fly by quickly). I figure I need one or two more sessions before it makes sense to look at the mirror with a tester again.

At the Astronomical Unit Telescope Workshop, I worked on my mirror blank for about an hour with center-over-center strokes using the new 10-inch tool that TW and I made recently.

At the well attended workshop, I worked on the mirror with the 6-inch tool that I am borrowing from Tom W. Center-over-center strokes with CeO for about an hour. Tim C and others discussed our plans for the Makers’ Faire that will take place at the Santa Barbara Museum of Natural History in July.

Worked on the mirror with a fresh batch of CeO. At first, just like toward the end of my previous polishing session, I was hearing unnerving, extremely high-pitched squeaks on every 3rd or 4th stroke along the same axis. Eventually, with additional polishing agent and after lifting the tool a few times, the noise went away. Interestingly, the pitch was so high that others in the room were not even hearing it.

Worked on the mirror with the small, 6-inch tool. Tried butterfly and cordal strokes for the first time, settling on the latter as they seemed easier. I was working the unpolished ring roughly half-way up the radius. This ring was not visible to the naked eye, but the laser indicated it clearly.

Worked on the mirror at the workshop with the 6-inch tool for the first time. Performed conservative center-over-center strokes with the intention of finishing the unpolished area in the center.

Today at the Telescope-Making workshop of the Santa Barbara Astronomical Unit, Tom and Tim demonstrated their techniques for cleaning telescope mirrors. I video-recorded the session and it is available in edited form on YouTube.

Just keeping track of time spent on the mirror.