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

[Richard Ozer <rozer@pacbell.net>]

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
> 
> 
> 
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