Re: ATM Fast hogging with pipe fitting

["Bob May" <bobmay@nethere.com>]

With a iron tool, about 1/4 teaspoon is more like what is needed as if you
stack the grit on top of each other you just end up grinding grit rather
than the mirror.
You will also want to start opening up your motions so that the curve goes
out to the edge of the glass.  You do want something resembling a sphere
when you actually start to make the tool or the tiles won't go into a nice
spherical shape and you will spend a lot of time getting the tile tool fully
working.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
----- Original Message -----
From: mike <crawford@goingware.com>
To: <atm@shore.net>
Sent: Monday, June 18, 2001 5:15 PM
Subject: ATM Fast hogging with pipe fitting


>
> I started rough grinding my 8" plate glass blank day before yesterday.
>
> I was going to use a pipe cap, but ended up getting a 2" to 1.5"
> coupling because they didn't have any large caps at the hardware store.
> The small end is a nice size to hold in my hand.
>
> The hogging has gone astonishingly fast with this tool.  In 20 minutes I
> had a noticeable curve, but could not measure it with the spit test.  In
> 40 minutes the radius was 110 inches, in an hour it was 89 inches,
> another half an hour it was 68.   I plan to make it a short focus
> mirror.
>
> I've only ever rough ground with full size tools before, mostly plate
> glass but once I rough ground a 7" with a tile tool.
>
> Only the inner six inches is getting consistently ground, and it's
> hardly being touched at the outer half inch.  So I'll need to use the
> tile tool I'll make shortly to bring it to a sphere.
>
> The abrasive is also being used up alarmingly fast.  I'm recovering some
> in the water bucket, but I seem to be able to break down a teaspoon of
> #80 carbo in less than a minute.
>
> It feels really good to be grinding glass again.  It's been too many
> years.  I should have taken this back up a long time ago.
>
> I'll be chronicling my scope projects at
>
> http://www.geometricvisions.com/atm/
>
> Mike Crawford
> crawford@goingware.com
>
>