Re: Fwd: [ATM] Open Question Concerning Pitch Laps

[Bryan Stiles <bryan.stiles@gmail.com>]

Mike

1.Blank is Pyrex. Full thickness (~1.33" I think)
2. Lap is Lab Stone from Modern Materials. ~1.5.-1.75" thick
3. Pitch is now about 1/4 - 5/16" at edges
4. Facets ~1" sq.  Channels 1/4" wide 3/16" deep
5. 2-3 hrs. Seems to vary with type of pressing (cold or warm) (weight or not)
6. ~ 8-10 lbs.
7. Yes I typically do remove the lap prior to beginning. To add CeOxide
8. To start a new session, I'll press about 20-30 minutes. Work glass
about 15-20 minutes. Rinse off lap and glass. Check progress. I'll do
this about 3 or 4 times before pressing again. Sometimes however I'll
press sooner if I get skipping, jerking, etc.
9. The hole was 4.25" in diameter. Depth I have no idea as I couldn't
figure out how to measure that. The rest of the mirror is spherical.
Except now I have a wicked narrow turned edge. (Another reason to go
back to fine grinding)
10. Cerium Oxide in a mix of water with a couple of drops of Dawn
dishwashing liquid.
11. Well I figured I'd want to make a new lap because the one I have
seems to have some performance issues. However If I pressed and got
good contact then maybe I could continue with this one. I actually
ordered more pitch today in preparation of making a new one.

Bryan


On Mon, 28 Feb 2005 16:59:47 -0500, Ken Lowther <hermit@outofoptions.org> wrote:
> 
> Quoting Bryan Stiles <bryan.stiles@gmail.com>:
> 
> > I did not scrape or brush the lap. Is there some guideline I should
> > use to recognize when to do this? Now at the outset I didn't wash the
> > lap off after use. Eventually the CeO mix built up and I used a soft
> > brush to remove that and generally clean it up a bit. I should also
> > mention that when not in use I store the lap in a plastic, sealed
> > container.
> >
> Well, when the lap start not to work, that is an indication you may
> need to rough up the surface and brush away the embedded glass and
> polish. I once had a lap that moved like 'silk'.  Nice feel but was
> doing nothing. ;-)  You should still feel the drag.  I meant to say "Is
> your lap too thin?".  That will affect it also.
> 
> Ken
> 
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