[ATM] Hogging!!!

[Guy Brandenburg]

I would do irregular circular strokes that mostly hit the center. If you can handle mirror on top, it'll go fairly quickly. Tool on top will do, also, but will be slower. (biggest I've done is 16.5"). I would recommend the ring out of all of the choices you offered.

KR <kreid at primus.ca> wrote: Hello Georgia,

Even 5" seems a little big to dig out the centre. (I used a 2" pipe cap on a 
10"). Once you get the centre going, coc,  you can resort to chordal
strokes inside or up to the edge. However you seem to like constructing 
things. How about a spherometer? I found it a very reliable way to determine
 how spherical things were going. Even a 3" straight edge with a dial 
caliper mounted in the centre would do ( a la Richard). You grind until you 
have the same
measurement over the entire mirror. There's no guessing. Have fun!

another humble novice, sometimes
KR

----- Original Message ----- 
From: "Norm Prince" 
To: 
Sent: Saturday, January 20, 2007 4:47 PM
Subject: [ATM] Hogging!!!


>
> What i really wanted to ask about though was subdiameter tool hogging. 
> I've selected three canidates for the 12" blank.  They are as follows: an 
> almost 5" piece of plate steel (from god only knows what)...an almost 6" 
> ring (outer housing of a big roller bearing), and a 4.5ish grind stone 
> (granddads ole time axe grinder...just thought it might save me the 
> grit???).  I would be so delighted to hear the range of opinions expressed 
> about which is the best choice.  I posted a pic of the canidates along 
> with a pic of the edge grinding set up at 
> http://mysite.verizon.net/cmb15s7x/temp.htm
>
> ...but what i really need some input on is strokes for said sub-diam 
> hogging.  Are these CoC?...tool on top or mirror???...and length of stroke 
> is a bit of ??? too...almost to the edge?..how much is almost?  I've only 
> made 8" mirror to date, and i used a full diameter tool; grinding almost 
> exclusivly mirror on top...any input would be greatly appreciated.
>


"Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved."
- wtote Charles Darwin.
Guy Brandenburg, Washington, DC
My home page on astronomy, mathematics, education:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
or else 
http://tinyurl.com/r6fh2