Primary Mirror Page
Polishing:
Carrying on with the lazy theme I decided to polish this big brut the fastest way I could. I guess I should clarify that point because I started polishing in September and in January I am still not done. I meant to say that with the least amount of effort.
My plan was to use polishing pads to polish out the glass then switch to a small tool using pitch in combination with cerium oxide to give me a nice even surface. The finale will be a slow and careful smoothening of the surface with jewelers rouge. Parabolizing will be done with rouge.
I started my polishing operation using the last fine grinding compound in combination with the pads for a 45 minute surface prep. I followed this step directly with cerium oxide and as of today I have a total of 4.5 hours of polishing time into this mirror and I estimate that I am about 60-70% complete. As of January 18th, 2003 the inner 18" of the mirror is polished out. I am absolutely amazed how fast this mirror is polishing. My 12.5" mirror took about 15 hours to polish out. An added benefit of the pads is that the focal length does not change so you can polish all you want without fear. I also noticed that my edge is completely clean with no sign of being turned up or down. I will never polish out a mirror with pitch again!
I discovered that polishing with pads can be done the hard way or the easy way. Using pitch you want a high degree of friction between the pitch and the tool in order to polish quickly. I noticed that with the pads they seem to polish just fine with lots of water. Lots of water = lower friction. Low friction means that my arms will not fall off. Anyone who ever tried polishing a mirror with a 20" tool knows exactly what I mean!
The photo to the left shows the essential items absolutely required to polish out a large mirror. Item #1 is lots of good beer. I learned that trick from a fellow ATMer in Germany who has worked on larger projects than this. Item #2 is 3 dowel pins to keep the mirror from falling off the table. I had a few close calls on that front. Item #3 is a piece of cushiony carpet used evenly support the bottom side of the mirror in order to help control astigmatism. I inserted the carpet inside a large garbage bad to keep the contaminants off of the mirror surface. Those are folds in the bag NOT scratches. BTW notice the centre (<-- Canadian spelling) mounted handles on the tool. I read about this on the ATM list. Looks like it actually works!
The photo on the left shows the polishing tool with the polishing pads. Again I am absolutely amazed how well these work. These are the original pads and I fully expect them to last the duration of the work. I clean them with water using a tooth brush after a few hours of use.
This image is a photo of my slave. His name is Steve and he lives in St Louis. I'm ashamed to admit that he's done 1/2 of the polishing during our Christmas vacation. Hey Steve, you need to come back to the cold white north and help me finish this thing! With or without his help I plan to have the polishing done by mid February.
In summary - so far so good. Astigmatism seems to be OK and the Ronchi test looks very promising. The mirror was slightly parabolic so I had to shorten the strokes. My hopes remain high!
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