Re: ATM FIRST MIRROR

[astillma@nit.AirTouch.COM (Anthony Stillman)]

Richard,

I'm some what supprised that the kit contained 46 grit and that after 40 wets
you are only half as deep as you need to be (about a thrid the total material.)
This implies (assuming that you are applying enough pressure) that the material
is rather hard.  This is a good thing as 46 grit silicon carbide does a great
deal of sub-surface damage.  I have only used it on quartz and even there I
finished hogging with 80 to remove any damage I instilled with the 46 grit.
The advantage to hard material (you already know the disadvantage) is that it
polishes well, further it can be slightly easier to figure.

As to your questions.

I have not worked with that specific material, but I have worked with materials
much harder than pyrex (~5.5 on the mole hardness scale) and even quartz (7-7.5)
Assuming that you are not getting a lot of chipping and the material is about
as hard as quartz (do a scratch test) you should be on with 46 grit.

Grinding with a 1/4 extra of tool really shouldn't be a problem, but when you
polish make the lap either the same size as the mirror or a bit smaller (~<1/8
inch) otherwise you will end up with a turned down edge.

Good Luck

Anthony