Re: ATM 24.5 inch binoculars or f/8?(longer yet)

["tdfullmoon" <tdfullmoon@koan.com>]

>I would be very interested in learning from your experiences in slicing the
>blank.  Could you please post a message detailing the method that worked
for
>your project.
>
>Hervey Lemay
>Brooklyn, NY

Harvey,
You have a thick blank you'd like to make 2 from, or just a
masochist?(kidding)
I'm an 8 w.p.m. typist,(whine, whine) but here goes..
My first design was a reciprocating solid wire saw rig using a gearmotor
mounted on a 2x4 rig which sandwiched and slid down the glass (which was set
on edge) as it cut. gearmotor had offset pin mounted on the output shaft of
the gearmotor, which the cable attached to, with a variable stroke length.
The other end of the wire was heavily spring loaded to the other end of the
carriage.
With this set up, the cut started to wander off center after it got about 3
inches into the glass.
Next design spun the whole disk on a turntable at about 180 rpm angled about
60 degrees. I had the idea to use a 14 inch cut off saw blade at the end of
a spring loaded swing arm and attached it to the turntable so that the blade
lined up with the groove I had already made. Starting the turntable with the
blade into the groove started the blade "smacking" into the bottom of the
groove every time it came around(scary), so it had to be springloaded
exactly right until it wore in a better curve, and eventually ate up the old
groove. Then I could apply more springloading and the work went faster. To
keep things moving smoothly and coolly, I also built in a drip emitter
system aimed at the point of contact.
The work went on until there was only about  5 inches left uncut in the
middle of the blank. This took a LONG time. Fortunately The private airport
I work at likes me enough to let me do all this in-between working on the
planes! I decided that to continue spinning this 24.5 inch disk at 180 rpm
was risking creating an expensive one shot Frisbee if continued, so I
stopped there. Cutting the last 5 inches out of the center would be the most
dangerous phase.
I lengthened a carborundum  coated cable by brazing it between 2 lengths of
.08 (ish)regular solid wire cable and then brazed one end of this to the end
of the blade on my reciprocating saw. I then springloaded the other end of
the cable at the proper height, to my workbench, which I laid my disk on,
and slid the cable into the groove aligning the gritted part with the uncut
section of the blank. Next I shimmed the groove all the way around, so that
the glass didn't crush itself as I removed the center section. I had to
angle the glass slightly so a drip emitter would bring water to the center.
Turned on the saw and started cutting. Had to replace the blade a few times
to get through the last 5 inches. Started making my own as those things are
expensive! The last 1/4 inch was the most hair raising, as it was off center
and a chip/crack here would have been bad news because it would not be
covered by the secondary. Fortunately the shims held all tightly in place at
the last moments. I cant tell you how it felt to watch that last tiny bit of
glass disappear!
I never thought I could have afforded one 24.5 inch blank, much less 2!!!
only cost a hundred bucks....and a few weeks(har har)
Still want to hear from you folks on my question about my other blanks
destiny...anyone ever looked through a 24 inch bino...is it worth the extra
work(I know it's subjective...subjective opinions wanted!) How about an f 8
monster...anyone ever looked through something like this? This is the way
I'm leaning, as a 16 foot climb to the eyepiece is somehow a romantic
thought to me(shades of tombaugh)
Now going to go soak my typing fingers (both of them)
Dave
Message-----
From: Lemay, Hervey <HLemay@Segalco.com>
To: 'tdfullmoon' <tdfullmoon@koan.com>
Date: Friday, April 16, 1999 8:53 AM
Subject: RE: ATM 24.5 inch binoculars or?(long)