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Re: [ATM] Generated Tool does not Match Mirror Blank
My 2 cents worth here: the MidAtlantic Mirror Making Weekend has been
using pregenerated mirrors and tools
from Newport Glass for 5 years...we have bought over a hundred sets. The
pregen glass curves are clean and
the tool/mirror fit very well - both pieces are ground flat on the back
and chamfered on front and back. The surfaces
are very smooth(such as a 400 or 25micron would leave). We have always
started with 220 to ensure a good fit
but I sure would like to try one beginning at 25 micron because the
surfaces are so very smooth.
BTW, we begin with 220 carbo, then 25M, 12M & 5M aluminum oxide, then
polishing pads with CeO2, then pitch with
CeO2 for final polishing and figuring.
And, I have to say, some of our first time mirror makers have made mirrors
that leave me envious of their success.
Don...
Richard Ozer <rozer@pacbell.net>
Sent by: atm-bounces@atmlist.net
10/08/2005 03:21 PM
To
Dave Jack <dave.jack@glass-beads.net>
cc
atm@atmlist.net
Subject
Re: [ATM] Generated Tool does not Match Mirror Blank
Dave,
Just start grinding. Tools never match the mirror at first contact. The
two surfaces
have to be broken in to match one another. If the mirror is
pre-generated, you'll need
to flip from mirror-on-top to tool-on-top periodically in order to
maintain the current
curve.
It should take less than an hour of course grinding for the two surfaces
to match
perfectly. Just use the most course grit in your kit to achieve this.
RO
Dave Jack wrote:
> Hello all;
>
> First off I would like to say that I have been reading this list with
some
> interest for a while now and have been really pleased to see the level
of
> enthusiasm and knowledge that its members have and share on a regular
basis.
>
> I decided to grind my own mirror having never owned a telescope before
and
> thought I would start with a generated 8" f/6 kit so as to make my first
go
> of it a bit easier. Call it a safer bet or a bit of laziness I thought a
> generated curve would be easier to work with my first time.
>
> So here is the rub: after waiting 5-1/2 months for the kit to arrive I
now
> have a great looking mirror blank ready for fine grinding but the tool
is a
> bad fit. The tool has a 1/4" dia. flat spot in the middle. If you place
the
> tool on the mirror you can spin the tool like a top (it makes an awesome
top
> btw). For those who have seen curve generating done I think this means
the
> blank was not centered prior to generating the curve so I have a flat
spot
> and probably the curve of the tool is slightly different from the
mirror.
>
> Given that I have waited 5-1/2 months for the kit to arrive I would
rather
> fix this than send it back. Do I need to go back to rough grinding or
will
> this sort itself out with a normal W stroke at #220 grit(my corsest
grit)? I
> have a fear that this would create a mirror with two radiuses, would I
be
> best to go center over center until the tool and the mirror appear to
mate?
> Will I need to find some corser grit? Newbies always have so many
questions
> so thanks for your suggestions and patience.
>
>
> -Dave Jack
>
>
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>
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