Re: ATM chasing spheres $%$^&*(%^&$%^!!!!!

[Cary Chleborad <bennu@ns.net>]

Cary Chleborad wrote:
> 
> Ok... I recently acquired an over-arm type grinding machine.  The arm
> is manually controled i.e, you grab the handle and push it back and
> forth.  The table turns at about 30 rpm - counter clockwise.
> 
>         I've been grinding an 8" and I'm having trouble acquiring a shpere.
> I'm using a channeled aluminum tool (TOT) and stroking from center to
> left at about 10 strokes a minute.  I've tried stroke lengths from 1/8D
> to 1/3D and I just can't seem to get a sphere. I'm talking about a rough
> sphere, I'm in 120 grit stage and usig a graphite test.  Also, I don't
> think I'm being impatient, because I've spent five hours on 120 chasing
> spheres.  Any ideas?

OK.. being the hard head that I am, I just couldn't let things
rest...I've done more work and investigation.

#1 I'm using and aluminum tool 3/4" thick.  Since I was applying
pressure to the over arm by hand, I thought that I might have been
getting carried away and flexing the tool (doesn't seem likely).  I
added approx 4 pounds of weight to the pin & stopped applying pressure
by hand.

#2 I'm using exactly 1/4" D stroke now.

#3 Using a graphite test ( I draw a cross-hatch pattern on the mirror
and work it over the tool using 1/4" strokes) reveals that I have a
raised ring from about 37% to 75% of r.

I'll be damned If i can figure out what is going on...help! (please?)

-Cary Chleborad