Re: ATM Beginning my 16"

[Mel Bartels <mbartels@efn.org>]

> 1) Is f/5 too deep for this mirror? I am thinking f/6 would be
> safer. Opinions?

It is not like there is a sharp boundary never to cross, but I would stay
f/5.5 or slower.

> 1.5) I thought I could hog the blank using a pipe end flange, as I
> have heard some people do. Is there a better way? Are there gotchya's
> with this method?

This is a terrific method with plate glass.  I hogged out a similar 16
inch to f/6 in something like 3 hrs

> 2) I thought PLOP would recommend the number of support pt's for a
> given diameter, thickness, f-ratio, and type of glass. But it makes me
> pick the number of pts. Can I assume 18 is completely adequate? Or am
> I looking at 27 even at f/6?

Tom Krajci has proven that a 6 pt supporting a thin 16 inch is quite
adequate.

> 3) Have there been better (lighter/stronger) tailgate designs since
> the Berry/Kriege design in the Large Dob's book? Or is that still the
> sweet spot in simplicity and functionality? Links to alternatives?

Well, if you only need 6 pts, then it's gotta be simpler and lighter!

Don't let the sling stretch.  I used sheet metal covered with auto bumper
vinyl.  There are other ideas.  Actually, two simple edge supports coated
with teflon spaced at 90 degrees works well with this mirror size.  Dump
the sling.  Or, consider gluing the mirror to the support points with 1/8
inch thick RTV.

Mel Bartels