Re: ATM Advice with Flexing a 16"

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

Peter and others,

SORRY about the misunderstanding. It should have read hog out the back
convex..
After reading Alan's article I assumed everyone understood that the optimal
back shape
for a flex mirror is CONVEX.The program will calculate the radius by
entering 0's
for back shape and taper exponent. The exact radius of the convex back is
not critical-
generally a meniscus with a back convexity approximating the front will flex
to an elegant
figure.

I read wedge from the back with the mirror face down on a plate glass
support and positioned
against two posts at the edge.. A dial indicator overhangs the back of the
mirror.
The photo in the Nov. 2000 S&T article shows the set up for measuring
sagitta and wedge.
A micrometer reading around the edge will serve as well.

And yes- my meager web site, www.flexmirror.com . needs some real content,
photos
and illustrations.

Again- mea culpa- sorry if I misled you.

Bill Kelley

.


----- Original Message -----
From: "Peter" <peter@kitgear.com>
To: "Bill Kelley" <flex@commspeed.net>; "Ken Hunter" <kb7h@onemain.com>;
<atm@shore.net>
Sent: Friday, January 17, 2003 9:07 PM
Subject: Re: ATM Advice with Flexing a 16"


> 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
> >