Re: [ATM] Generated Tool does not Match Mirror Blank

[Ken Hunter <atm_ken_hunter@yahoo.com>]

Hi Jack...
 
220 Grit will be fine to start out with unless you have a very large difference in focal length (sagitta's). You should be able to get them mated within an hour or so of grinding. By the way, this is not an unknown event so don't feel too bad or throw rocks at the supplier (except for taking so long to get you the glass kit).
 
Here's something you will no doubt hear again...
 
Grind more - worry less!
 
Welcome to the best hobby in the world!
 
Ken Hunter
 


Dave Jack <dave.jack@glass-beads.net> 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



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