Re: ATM Coring Speed

[Dennis Rech <dennisrech@home.com>]

At 04:47 PM 7/16/99 -0400, Aplanatic@aol.com wrote:
>
>I am designing a polishing machine and wish to use it to perforate a 13" 
>diameter mirror.  The perforation will be 4 inches in diameter.  The mirror 
>will turn and the coring bit will remain stationary.  What is a good 
>rotational rate for this operation?
>
>Thanks,
>
>Dave Rowe
>Torrance, CA
>Medium Format Astrophotography:
>http://members.aol.com/aplanatic/photos/astro.html
> 
Notice: I have only done a couple of cores, so this advice may not be real
good. 
You may as well run the machine up to 100 rpm or so or you will be watching
the process for a long time. 
I found that 120 to 180 grit cuts faster than 60 or 80. The heavier grit
has trouble working its way to the glass.
Unless the mirror is bedded into plaster or something else, the bottom of
the hole will chip out in a big ugly fracture when the core drill starts
grabbing on breakthrough. 
If you use too much weight, the bottom will spald for sure. 
Make sure that your core drill has some flutes at least as long as the
thickness of the glass or else the drudges will have no may to come up out
of the hole.
Let us know how you do. 


Dennis Rech
Mirror-o-Matic

http://members.home.com/swwas/mirror