Re: ATM Advice with Flexing a 16"

["Bill Kelley" <flex@commspeed.net>]

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
>
>
>
>
>