Re: [ATM] Problems With Central Hole Unchanged

[Ken Lowther <hermit@outofoptions.org>]

Short sessions with pressing in between.  You may try cutting a star 
out of wax paper and press it into the lap where the hole is.   That 
will stop it cutting.

Ken

Quoting Bryan Stiles <bryan.stiles@gmail.com>:

> Good Evening Everyone, I am hoping that someone out there can give me
> a hand. I am working on a 8" f/6 mirror. When I attempted to figure
> this mirror, I worked about 15-20 with a W stroke. Apparently my
> stroke was too long and this produced a nice hole in the middle of the
> mirror about 4.25" in diameter. I have worked to try to get this out
> for about 4-5 hours now and don't seem to be getting anywhere.
>
> Here's what I have tried:
> 1. MOT 1/3 COC. This didn't really do anything that I could see.
> Quickly abandoned this method after about 30 minutes.
> 2. TOT 1/3 COC. This seemed to smooth the hole somewhat but not get 
> rid of it.
> 3. Cut a paper disc the size of the hole and cold pressed for ~30 min.
> More TOT 1/3 COC.
>
> The dang hole is still there. I have warm pressed, cold pressed, with
> mesh (microfacet), without mesh, more pressure, less pressure, thicker
> CeO and thinner CeO. I feel that I'm getting pretty good contact but
> I'm getting nowhere fast.
>
> I am looking at my mirror on my Foucault Tester (Homebuilt Stellafane
> Type) with the razor edge and Ronchi grating. The blade is coming in
> from the left and I am assuming the light to come from the right (thus
> a hole not a hill). When using the Ronchi grating (100 lpi) the lines
> will hardly deflect when crossing the hole.
>
> I am using soft burgundy and have rechanneled my lap 4 times now and
> am closing in on the fifth.
>
> I am seriously considering going back to 500 grit and trying it that
> way. I have really enjoyed making this mirror and don't mind the extra
> work but I am losing my patience with this problem. Any helpful advice
> would be very much appreciated.
>
> Thanks, Bryan
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>

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