Re: [ATM] Sleeks or scratches?

[Mike Lockwood <melockwo@uiuc.edu>]

David,

David Grennan wrote:
> I'm fairly certain from reading all the guys posts that we are talking about
> sleeks here.  I can only see them in the right light.  When catch the light
> just right, I can make them dance around the mirror by jiggling it just a
> little.

Then they should polish out in a reasonable amount of time.  Inspect 
the surface with a 10X loupe if you can, and check your progress after 
a bit of polishing.  They may vanish quickly.

> As for the cerox.  I've no idea of its providence.  I was given it (and the
> mirror kit) by a member of out astrosoc who never got around to making the
> mirror.  It was almost certainly from a UK based supplier, probably
> galvooptics or beacon hill.  Heres a point.  I know the cerox lay unopened
> in its bag for over five years.  Does cerox have a shelf life?

Not unless it gets moist and forms hard clumps.  These should be 
removed, or carefully broken up before use, with care taken to make 
sure they are no longer present.

> I also know now from reading some more posts that I was waay too heavy
> handed with it.  My mixture had the consistency of thicj cream.  Whereas I
> understand from some posts it should be more like weak milk!!  Well thats
> the great thing about ATM, your always learning.  I'm amazed I even got this
> far!!

Thin milk is good for real polishing, when you are trying to remove 
pits (or sleeps).  Often it will get even thinner than that, as you 
spray on water.

> I suspect probably a little hard.  From start to finishing polishing I've
> had to trim twice.  I suspect 3 or 4 times would be the norm for pitch of
> the proper hardness, over the period of 6 hours polishing.  I've read and
> understood the posts re flambeeing the lap :)

Well, if you polished 8 hours, trimming every 4 hours is fine.  For my 
taste, it's a little on the hard side for figuring, but good for 
polishing and spherizing.  Many have different preferences and 
techniques.  There is more than one way to make a good mirror.

I also should note that with your thick polishing mixture, the 
friction while polishing might not have been as great, and the pitch 
might not have flowed as much as it would have if the mixture were 
right.  So, the pitch might just be softer than you think.

> However before I do that I'd
> like to clean off all the cerox which is encrusted on and between the
> squares.  Would it be okay to use a soft new toothbrush for that purpose?

Yes.  I keep an old toothbrush for this purpose.  Don't worry about 
the old Cerium in the squares - it will soon wear out and the new 
cerium will take over.

> I am tempted to rebuild the lap with new pitch, however this mirror is more
> about learning the art of mirror making than the finished product.  I never
> expected to make a world beater mirror on my first go anyway!  I'd rather
> spend the time learning how to figure the mirror than making new laps!

Keep the lap for now.  You can always warm it slightly in water before 
a press and figuring spell if you think that it's too hard.

> I've tossed every grain of the old cerox out and ordered new stuff which I
> will decant a couple of times before use.  I ordered a lot so that I dont
> have to be too miserely with the decanting of it.

Okay.  You might have been able to decant the old Cerium, but it's not 
a bad idea to know the origin of your materials.

As several have mentioned, filtered water is a good move if you don't 
know the quality of your supply.  I'm lucky - we have good tap water 
where I live.

Here in the US, I like Cerox 1670 from Salem Distributing for fast 
polishing.  This stuff removes pits fast, and it seems to be of fairly 
uniform size (no sleeks).  I use slower stuff for figuring, but you 
can figure a smooth mirror with very dilute 1670.

	Mike Lockwood


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