ATM Spherizing at the end of rough grinding; Carbo consumption

[John Maxwell <jmax@toad.net>]

Thanks to all who responded to my question about checking tool/mirror
contact; I went with the "Sharpie test", just 'cause it didn't involve
any possibility of my fumblefingers contaminating fine grits.

*Wonderful* contact; the marks were gone well before the end of a wet.
Happy, happy, joy, joy.


Now, another newbie type question: Why the @!#*%@! am I going through
Carbo so fast?

I'm using an 8" WB kit.  Despite advice from Bratislav and others to make
a tile/plaster tool, I'm using the Pyrex tool that came with the kit; I do
figure on eventually reworking the tool into another mirror, but I wanted
to try the "traditional" method first.

>From previous comments on the list, and from comparing the quantities of
abrasives supplied by WB with recomended quantities in Tex. and ATM, I
thought the kit contained about twice as much #80 as I needed...  but I am
*out*, and I'm still about 10" long on focal length!  (i.e., about 1/160" 
left to target sag.) 

I'm considering just stopping here (at f/9.3), but am reluctant, both for
the sake of tube length and 'cause many people have said that Focault
testing gets kinda hard after about f/8.

Possibilites that come to mind:

- Too much or too little water? I have cut down considerably on the water
  used in each wet from when I started; I now use just barely enough to
  wet all of the Carbo grains. 

- Stroking too fast? After checking my references, I dropped down
  from ~80 strokes/min to ~40.

- Switched from chordal strokes to W strokes too early? I switched when I
  had about 1/80" left to target sag.

- Alien abduction of my abrasives?

-----------------------------------------------------------------------
John Maxwell                                              jmax@toad.net
"You have the ability to learn from your mistakes. You will learn a lot
today."