Re: [ATM] RE: mirror grinding

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

ntent wrote:
> Damn.... it seems that a brake rotor would be a very nice tool, indeed; 
> easy to hold on to, and the mass of it would help do the work.  Also, 
> wouldn't the "porosity" in the cast iron help hold onto the grit?  Great 
> idea if it would work; and since an "end cap" (closure) for an iron pipe 
> will work, I don't see why a rotor wouldn't work. Possibly the only 
> difference being the rotor being softer (Rockwell)........

I think I've heard of someone else using a brake rotor... try 
searching for "brake rotor" in the ATM list archive and you might turn 
it up.

Many excellent ideas have been shared on this list, so if you have an 
idea, try searching for variations of it first.  You may turn up 
suggestions and tips that may improve things further.

I think the key things to remember in hogging out a curve are that 
metal rings work fairly well (rotor, pipe cap, etc) because the grit 
can easily get under them, and the metal doesn't grind away quickly.

However, for hogging with a pre-curved tool of metal, glass, tile and 
plaster, etc, (not a ring, a circular tool) it is important to have 
some channels so the grit can circulate and cut glass.

In one of the three ATM books, the importance of having a channelled 
tool during fine grinding is highlighted - it improves the quality of 
the grind, mates the two surfaces better and generates a better sphere 
(leading to faster polishing with fewer edge problems), and works 
faster than a solid tool with no channels.  A valuable fact for those 
in the micron-range of abrasives.  A few minutes here can save hours 
or days of hard polishing work.

Also mentioned somewhere in one of the many Willmann-Bell ATM books 
(possibly the Maksutov Circular collections) was the use of a flexible 
"sanding pad" with diamond impregnated in it.  This was used by hand 
to do some of the hogging out of a very fast 17.5" mirror, I believe. 
  No spent grit to clean up - just milky white "glass juice".

	Mike Lockwood

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