Re: [ATM] What a wonderful sound!

["Bob May" <rmay@nethere.com>]

Floor tiles like the ones in the public bathrooms are the hard
ones and what you want to use.  Nickels also work well although I
haven't tried them - just don't see the need for using coinage
for something like that.
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net

----- Original Message -----
From: Bill Wheaton <junkwheaton@gmail.com>
To: David Harbour <stainless_steel@suddenlink.net>
Cc: Bob May <rmay@nethere.com>; <atm@atmlist.net>
Sent: Tuesday, May 06, 2008 7:35 PM
Subject: Re: [ATM] What a wonderful sound!


> I tried it with the small 2" hogging tool at the edge tonight.
It
> looks like it worked.  The hole is shallower now, and I have it
all
> within .0055 +- .0015".  A little more grinding like that, and
I'll be
> in good shape - maybe a half hour or so.  Getting the hang of
this.
>
> Then I need to find some dental stone and some tiles.  I need
to talk
> to my dentist anyway... (oy).
>
> So how do you know if the tiles are the "hard" sort, and not
the
> "soft" ones.  Is it pretty obvious when you buy them?  I was
going to
> get the square ones so it would be easier to clear the channels
rather
> than the hex ones.
>
> I do have a bunch of nickels, could I use them instead?  Would
it work
> better?  I saw something about that in the archives, but I'm
not
> certain if it was simply for hogging or not... I think it was.
>
> -Bill
>
> On Mon, May 5, 2008 at 10:21 PM, Bill Wheaton
<junkwheaton@gmail.com> wrote:
> > So, I'll split the difference between "just do it" and
"detail nut"
> > for now, and come up with my own style eventually :)
> >
> > In many ways, I am both of your camps.... especially after
tonight.  I
> > spent about 45 minutes metal on glass time, trying to do
smaller, more
> > even steps around the barrel, and more even rounder strokes,
and got
> > into my "groove" so to speak (or lack of one, I hope!).  I
certainly
> > don't want to be sloppy about it, but I've also read that
randomness
> > is an essencial ingredient too.
> >
> > So, when I did my rough sagitta measurement it said 0.1230
inch. I
> > thought I was getting close enough to the target that I
needed a
> > better measurement method, so I made a sphereometer.
> >
> > I saw a suggestion (perhaps on your site Bob?) about making
one from a
> > pulley.  I happened to have a 6" steel pulley from an old
furnace fan
> > with a fairly sharp edge, so I ground it down slightly right
on my
> > mirror until it had a <1/64" flat ring on it and put my
digital dial
> > indicator in the middle of it with some bronze bushings, and
some
> > masking tape to make up the difference.
> >
> > I zeroed it on the flat back of the old glass tool I have,
and tested
> > the top of the tool in several places and got .021 to.022,
which is
> > just about at a 100" focal length, so I figure that I have a
fairly
> > good ring type sphereometer.
> >
> > Am I correct in how I am using it?  The measurements should
give the
> > sagitta of a 6" portion of the sphere, so looking at Bob
May's quick
> > sagitta reference page
http://bobmay.astronomy.net/misc/sagchart.htm,
> > in the 6" column, and found that .022 is 100" FL.  Does that
make
> > sense?  Also, I find that I am able to take readings right up
to the
> > edge, since its a ring.  I read somewhere that is one of its
> > advantages.  Is that right?
> >
> > Anyway, so applying that principle to the mirror then, I got
> > measurements of .026 at the edges, .030 half way in, and .036
at the
> > center. Its pretty consistant all around like that.  In other
words It
> > looks to me that I dug a hole, and now I will have to widen
it by
> > grinding the glass around the edges a lot more than I was
before.
> >
> > Now, Bob, you have said several times, grind where the glass
is (to
> > paraphrase).  I take that to mean in this case, to use the
two inch
> > pipe cap instead of the 3" pipe flange, and stay away from
the center
> > for now.  I suspect that the best course of action is to
grind it like
> > with short strokes around the edge, but measure often.  Do
you agree?
> >
> > But at what point do I say "hogging is done, time to pour the
tool"?
> > Should I wait until the sphereometer readings are all .032 +-
.001"?
> >
> > I find it amazing how fast this is going, I figured that I
would be
> > doing this a lot longer.  This is a blast.  Sure hope the
cool weather
> > holds!
> >
> > -Bill
> >
>

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