Re: [ATM] Spherometer & Hogging with Diamonds

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

Sounds like you had some fun with diamond blades!  Added a
comment (hopefully my typing was good) on working with diamonds.
You basically don't want to do too much weight on a diamond blade
or the diamonds will indeed quickly go away.  The blades are
designed for light fast cuts, not heavy slow cuts.  You can add
enough weight to where the diamonds will just roll away out of
the matrix that they are held in rather than actually be dragged
along the glass.  Your PIG was probably too heavy and it quickly
stressed the matrix so much that the diamonds walked away.
The spherometer article is a nice article on building a very
cheap spherometer for the purposes that you put it to, finding
out where the curve was wrong.  Ring spherometers are the best
ones to build as you can measure all the way to the edge of the
glass with them.  I should probalby build one soon as all of the
ones that I have build have been of the 3 ball type.  Their
advantage is that you can put on hardened steel balls on each of
the feet and not worry too much about the erosion of the ring as
you drag the spherometer across the surface of the glass when it
is not fully cleaned of SiC grit.
I'll also note that for your application, even just a bit of
threaded rod for the center can do the job as you just run the
rod down to contact and high spots on the surface will make the
spherometer rock about on the center.  Use 1/4-20 threaded rod
and you can even measure with a dial graduated with 25 marks on
it (the rod goes about 0.025" per turn!) so be aware of that
little trick.
Bob May

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

----- Original Message -----
From: <pauldkline@aol.com>
To: <atm@atmlist.net>
Sent: Saturday, March 15, 2008 10:59 AM
Subject: [ATM] Spherometer & Hogging with Diamonds


>
> How you use your spherometer will determine how much you want
to pay for it.? I just use mine to check for zones during hogging
and fine grinding, so I'm not concerned about the .0001
precision.? It's made from the bottom of a coffee can and an old
micrometer. http://www.pbase.com/paulkline/image/73491027
>
> While you are there, check out my hogging page?which
describes?the use and misuse?of?diamond saw blades to hog three
14" plate glass blanks.? One of them turned out pretty good :-)?
The other two are good too... only thinner.?
http://www.pbase.com/paulkline/hoggingg
>
> Haven't made much progress in a while, there's just too much
good stuff on tv ;-)
>
> Paul
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>

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