Re: [ATM] when to go to a pitch lap

[Mark Cowan <toolontop@yahoo.com>]

Hi David:

I believe you were asking about where to get enough
pitch at a reasonable price as well.  For organic
pitch Gugolz is the best, Salem Distributing has it
for $15.50 a kg, shipping will be $7-8 or so depending
on location.  Their service is excellent.  You'll need
more than a lb for the 14-16" or so lap you'll want to
pour, but pitch can be reused almost indefinitely and
tempered with turpentine as needed.  

How big is the plate tool you're using?  Be sure to
grind down below 30micron to around 9micron or so
before going to pitch.  

Also check for good sphericity - use a pencil or
sharpie marker to mark the mirror center to edge and
see that it grinds off at the same rate before you
commit to polishing!

Cheers,
Mark Cowan
Salem, OR
 
--- David  Williams <dwilliams1128@earthlink.net>
wrote:
> Hello ATM people
> 
> Does anyone know the right time to switch over to
> using a pitch lap for polishing?
> Right now I'm at 30 micron WCA (aluminum oxide) and
> I'm using a glass tool (all glass is plate glass), 
> The mirror is 20" diameter, 1" thick, f5, sagitta at
> 1/4".  I'm using a barrol to do the walk around.  I
> have some burgundy pitch, about a pound, but Newport
> Glass is pretty expensive.  Does anybody know of a
> lesser expensive way to go?  
> 
> By the way,  I can see a reflection of light off the
> mirror at an angle of about 20 degrees.
> And with the mirror dry I can reflect sunlight over
> to a tree and focus it to a ball about 2.5 to 3" in
> diameter.  Is this good?
> 
> Thank you for your help.
> David Williams
> dwilliams1128@earthlink.net
> _______________________________________________
> ATM mailing list http://www.atmlist.net/



	
		
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