Quote:
Originally Posted by Stefan Buda
Werner,
You need to get to much finer grit than 800 before the polishing with cerium oxide. I would finish the polishing with 9 micron aluminium oxide.
You must understand that no matter how flat you manage to grind your disk, it will not remain the same during polishing. That is why it needs figuring like any other optical surface. For that you will need to polish all three surfaces so that you can compare them during the many figuring stages. Unless you have a reference flat the same size that you are making.
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I will ring tomorrow to get #1000 (6.8 - 9.3microns) and #1200 (4.5 - 6.5microns). Have to get it sent up from Sydney. I hope he will post it out to me.
The three disks are 350mm and initially I thought I would make a pitch lap of 75% that is 260mm for the polishing. I did the grinding with a 1/4 stroke. Should I make a 350mm lap, there may not have to be a lot figuring to be done. I can cold press on one while I polish the others. I don't know if at the end of the 1200, there is going to be enough reflection to look at it with a newton interference meter. It works with the un-ground side of the glass. The fringes are all over the place. I got an optical flat, but only an 80mm one, should have bought a bigger one (maybe 100mm), but it would not have made a lot of difference.
At the end of all this, I will get the 1000 and 1200 grit. Should I make the pitch lap 350mm, do I need to make a pitch lap, Or can I use the three to polish against each other?