Re: ATM Advice with Flexing a 16"

["Peter" <peter@kitgear.com>]

Hi,

Good advice!

Should I grind the back flat before hogging it out because it has about
0.012" of waviness near the edge.

Thanks,

----- Original Message -----
From: Bill Kelley <flex@commspeed.net>
To: Ken Hunter <kb7h@onemain.com>; Peter <peter@kitgear.com>;
<atm@shore.net>
Sent: Friday, January 17, 2003 10:32 PM
Subject: Re: ATM Advice with Flexing a 16"


> Peter,
> My 2 cents. The back does not need to be fine ground. Hog out the front,
hog
> out the back to the same curvature, dewedge, clean up, fine grind the
front
> (checking for wedge on the coarser grits), polish and figure a sphere. A
#80
> grit surface on the back will not give you trouble working to 1/1000th
> wedge. An irregular bevel on the front might throw you off if you are
> reading wedge from the back with the mirror face down.
> Bill Kelley
>
>
> ----- Original Message -----
> From: "Ken Hunter" <kb7h@onemain.com>
> To: "Peter" <peter@kitgear.com>; <atm@shore.net>
> Sent: Friday, January 17, 2003 7:27 PM
> Subject: Re: ATM Advice with Flexing a 16"
>
>
> >
> > Unless you have a LOT of experience in optical fabrication and at least
a
> few mirrors under your belt, it's best to keep
> > both sides of the glass at the same grit level. Nothing brings tears
> quicker that a #80 scratch on a finished surface.
> > If you keep the wedge within a couple thousandths at #80 and bring it
> closer with each abrasive size (it's hard to make
> > wedge change if you are smoothing a spherical surface). You should not
> have to worry too much after the first coarse
> > abrasive sizes.
> >
> > Ken Hunter
> >
> >
> > ----- Original Message -----
> > From: "Peter" <peter@kitgear.com>
> > To: <atm@shore.net>
> > Sent: Friday, January 17, 2003 5:55 PM
> > Subject: ATM Advice with Flexing a 16"
> >
> >
> > Hi,
> >
> > I don't seem to be able to get much direct info on the flexing process.
I
> just wanted some advice regarding the best
> > order things should be done for a shaped back flexed mirror project. My
> mirror is 1" thick so I need to get the order of
> > events correct.
> >
> > Should I grind the front surface to the correct sagitta then grind the
> back to the same ROC and then finish the front?
> > Or, should I finish the front to the polishing stage then go and rough
> grind the back?
> >
> > There must be a defined method somewhere which yields the best results
and
> least amount of dewedging.
> >
> >
> > Thanks,
> >
> >
> > Peter
> >
> >
> >
> >
> >
>
>