Re: ATM Question to the list members: Re best use of polishing pads

["Bob May" <bobmay@nethere.com>]

Scott, if I've got you right, you made a tool and then buried the pads in
the surface?
The problem here is burying the pad into the surface of the tool.  This
makes the tool contact the glass and makes scratches a given!  The tool
should be cast and then the edges of it carved back to insure that they
don't touch the glass - the only thing that should be touching the glass is
the pads!
In addition, the saran wrap will put wrinkly marks on the tool and this will
tend to inhibit good contact.  Thus, only a few points of the pad will be
supporting the whole of the tool and that part will wear quickly.  Use some
vegatable oil if you want to cast a seperate tool for the pads as they need
a good matching surface that saran wrap can't give you.  Yes, I know that
you can smooth the saran wrap out very nicely but you have to realize that
the stuff isn't that even for thickness to begin with and now you're
stretching it to keep it from wrinkling and that makes for more difficulty.
I've always used the tool after grinding to put the pads on so there should
be an excellent match between the surfaces and even there, the pads aren't
made exactly enough to insure that the working surface of them is perfectly
matched to the glass.  After a bit of working, most of them are in full
contact but not always.
I might note here that a these pads we are using are intended to polish out
a 3" diameter piece of glass and be changed out after that polish so they do
have a limited lifetime.  The polishing machine is pretty much an Elgin
style machine and it works very fast and the surfaces that are polished onto
the glass are, by telescope making standards, quite poor for shape but
refractive lenses don't need the accuracy of the surface like mirrors do nor
do the resulting errors make a difference as the eye doesn't see though all
of the lens at one point thus 1 wave errors over the surface mean nothing to
the eye.
I don't know how often the pads are changed but the minimum is every lens
that they do.  Bob May
http://nav.to/bobmay
bobmay@nethere.com
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