Re: [ATM] industrial polishing pads?

["David Harbour" <stainless_steel@suddenlink.net>]

All-

I have seen this argument before; I believe the gentleman said that the pads 
DO NOT change the radius of curvature, becuase they are PARALLEL TO IT; they 
only bring the same curve forward by their thickness a little bit. Same 
curve, they say (this school of thought).

In any case, why not try some of the old remedies first- like Neale Howard's 
"shower netting" wrapped onto the tool, with abrasive in it, or perhaps the 
fellow in the old atm books who used "Honeycomb foundation" wax sheets?

It has always been my experience that "fortune favors the bold"- take no 
risks, be safe, and be mediocre. Just my two bits worth of nonsense; I 
stopped pushing glass 20 years ago (double back injury- no surgery allowed; 
two torn rotator cuffs; planter's fasciitis, acute rheumatoid arthritis). 
Only 40% use of left arm. Have to have friends carry my groceries up the 
stairs to the apartment. Enough of that- I could go on forever.

I hope I didn't stir up a hornet's nest, but it doesn't seem to me that the 
pads can change the radius of curvature, because, stuck on the blank, they 
have the same radius of curvature- I mean, the outer ones are not thicker 
than the inner ones; they are all parallel to the original radius of the 
tool. Correct me if I am wrong, someone. This is not my idea; I saw it on 
the list, long, long ago.

R-101/Davey

P.S. Or why not try a "pre polish" with 2 micron aluminum oxide directly on 
the lap? I have heaard of it done, with excellent results. Have to scrap the 
lap when you get ready for the rouge, though, and make a new one. But what 
is telescope making if not a hobby for "killing time" as someone said in the 
old Albert Ingalls/Scientific American telescope making, 3 volume set is 
about? (And having a good time, being challenged, etc.)

My particular nemesis was turned up edge; I ALWAYS got it; even when I tried 
to get turned down edge. Oddly, my first two mirrors polished out to a black 
polish with ROUGE in only 12 hours; I never got anywhere near a complete 
polish with Cerium oxide, thereafter. Odd. My first, an 8" f/5.6, was said 
by the club I gave it to, to be one fourteenth wave. My second, which I 
mounted was a 12" f/8 "Planet Killer"- my only turned down edge ever.

Carry on, Gentlemen, Gentle ladies; I will be lurking in the area.

R-101


----- Original Message ----- 
From: "Dave McCarter" <dmccarter@sympatico.ca>
To: "David Weinshenker" <daze39@earthlink.net>; "ATM List" <atm@atmlist.net>
Sent: Sunday, March 23, 2008 10:41 PM
Subject: Re: [ATM] industrial polishing pads?


>> I think these are the sort of "industrial fast polishing pads" that
>> all of the standard "telescope making" texts say are not quite suitable
>> for producing a final polish on the optics of an astronomical device,
>> but I am interested in trying whether or not they may have some virtue
>> as a "prepolishing" material to smooth the texture left by the fine
>> abrasive before continuing with a pressed pitch lap to refine the
>> surface to true smoothness.
>
> Don't do it!  When applied to the grinding tool to do a polishing session
> the pads add considerable thickness to the matched surface, and this 
> changes
> and lengthens the radius of curvature of the tool with respect to the
> mirror. The result is that the edge of the mirror is polished first and
> hard, which turns the edge. Precisely what you don't want.
>
> Pitch does not do this because while warm or cold pressing the pitch
> conforms to the surface of the mirror, taking on exactly the same radius 
> of
> curvature, so the turned edge does not occur.
>
> Dave
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


_______________________________________________
ATM mailing list http://www.atmlist.net/