Polishing with pads.

      You are probably wondering what pads are. In the eyeglass industry every attempt is made to make the polished glass or plastic as quickly as possible. One of the results that have gotten them to go faster is to use a paperlike pad to hold the polishing compound rather than the fickle pitch. The requirements for the shape of the surface are a lot more relaxed than what we are doing (they only need about a 1/2" circle to be within a few waves of spherical or so) while we want the entire surface of what may be a large mirror to be within a 1/10th wave of any other part of the surface. The thing that is nice is that we can do the rough polishing with these pads and get the big pits, etc. out of the surface and then pour a pitch lap and average out the little errors that get produced with these pads. There is an actual saving of time when you do things this way although you do end up spending money for the pads.

        If you're lucky, you may have a shop near you that actually makes lenses for eyewear but that's not a guarantee as not all optometrists bother to make their own lenses. Wholesalers for the trade sell a roll of pads for about $20-$30 containing several thousand of the self-adhesive pads on a carrier strip. Each pad is about 3" square inches in size and are shaped like an 8 petal flower. in a somewhat rectangular shape. If you're just going to do one mirror and want to try the pads method of polishing your mirror, you might want to find somebody who is using the pads and finagle a few out of him for your use.

       Pads are a moderately quick way to get the mirror polished in quick order. The problem that I have seen with the pads is that the figure is not very good although it takes only a little time to get the mirror to a spherical shape when you go to the pitch lap to do the finishing of the mirror. I might also note that I have never seen anybody successfully figure a mirror with pads.

       You start by applying the pads all over the tool (make sure the tool is good and dry and clean) and insure that they are in good adhesive contact with the tool. Then spread some Cerium Oxide and water mix over the pads and start polishing. The nice thing about this method is that you can indeed go fast with the strokes and even hang over side to side more than you would with a pitch lap. Applying pressure also seems to work well with this process. Don't forget to rotate the mirror and walk around the barrel as you do the polishing. I haven't seen anybody actually do a bad turned down edge with the pads so if anybody learns how to do a good spherical surface and then parabolize the mirror with pads, the pitch method will probably become obsolete as the method of finishing a mirror.

       After you have gotten a good polish, put the mirror on the test fixture and see what the shape looks like. You will probably see all kinds of strangeness in the shape with the Foucault test, including some or even most of the following: Central Hole, Depressed or Raised Ring(s), Strange Steps in radius and others. It is always interesting to see what shapes are generated by the pads and the interestingly, the shapes aren't guaranteed to be the same on several mirrors done on the same set of pads.

 After you have gotten the mirror fully polished out, it's time to go and make the pitch lap and finish up the mirror with smoothing out the surface and then figuring the mirror.