Re: [ATM] A polishing we will go!

["jcmulherin" <jcmulherin@opticalmechanics.com>]

Hi Ed:

Your overhang at the end of each stroke should be 1/6 of the tool diameter
or, in your case, 2". Some random variation in the amount of overhang is
good so don't worry about being too precise about it. Coc/Ws is the way to
go. Make sure you get the 1/6 overhang at the left and right end of the W
stroke.

James

James Mulherin
Optical Mechanics, Inc.
jcmulherin@opticalmechanics.com
www.opticalmechanics.com
Tel: (319) 351-3960
Fax: (319) 351-3943

> -----Original Message-----
> From: ed witkowski [mailto:edwski@comcast.net]
> Sent: Saturday, October 14, 2006 12:23 PM
> To: 'jcmulherin'
> Subject: RE: [ATM] A polishing we will go!
> 
> Hi James,
> Things look pretty good in the ronchi.
> Inside focus, smooth curves outward with some thinning at the ends.
> No zones :). A possible turned down edge visible in the outside of focus
> ronchi. Ref: http://www.atm-workshop.com/ronchi-test.html I'm getting the
> "hook" outside of focus.
> My stroke has been ToT, coc/Ws with about 2 to 3 inches of lap(12 inch
> lap)
> overhang.
> Should I shorten the stroke?
> Thank You and have a nice weekend.
> 
> Ed w
> 
> -----Original Message-----
> From: jcmulherin [mailto:jcmulherin@opticalmechanics.com]
> Sent: Monday, October 02, 2006 5:54 PM
> To: edwski@comcast.net; atm@atmlist.net
> Subject: RE: [ATM] A polishing we will go!
> 
> Hi Ed:
> 
> Nice to hear that you're getting started. Since you are polishing with a
> sub-diameter lap I would recommend taking a look at the figure right away.
> It's easy to lose control of the mirror's figure with a sub diameter lap.
> You'll want to monitor the figure as you polish to maintain a good
> spherical
> surface. Have a look at it with the Ronchi test and make sure the edge
> isn't
> turned or that you're not making zones. If things look good, just keep
> going
> the way you are.
> 
> Good luck!
> 
> James
> 
> James Mulherin
> Optical Mechanics, Inc.
> jcmulherin@opticalmechanics.com
> www.opticalmechanics.com
> Tel: (319) 351-3960
> Fax: (319) 351-3943
> 
> > -----Original Message-----
> > From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf
> > Of edwski@comcast.net
> > Sent: Monday, October 02, 2006 4:42 PM
> > To: atm@atmlist.net
> > Subject: [ATM] A polishing we will go!
> >
> > Greeting ATMers,
> > Having made an 8 incher and 10 incher, I wanted to go for the gusto.
> > Originally I was going to get a pregenerated 16 from Newport. Those
> plans
> > got delayed(luckily). A few weeks ago I purchased a ready to polish 18
> > inch from James Mulherin at OMI. The mirror arrived very well packed and
> > fine ground,  excellent! Looked too nice to polish. Our local mirror
> > making group meets at the NCA(National Capital Astronomers) mirror class
> > run by Guy Brandenburg(a big thank goes to Guy!).
> > We had a old 12 inch pitch lap. After softening it with hot water, we
> > pressed it with 100 lbs of weight. Then the journey began. I began
> > polishing with cerox 1670. On the first night, I only manged to put in
> 45
> > minutes of polishing. The center was beginning to polish out. :)
> > A week later, I cold pressed the lap for 30 minutes and began polishing.
> > Holy Pitch Lap! It is quite a work out, especially when you start to
> > squeak. 45 minutes and I needed a break. 15 minutes of cold pressing and
> > back to polishing.  All was great until I heard the most dreaded sound
> you
> > can hear while grinding/polishing. @$%&* I had scratched the blank!!.
> > There are a few, one or two that I don't think will get polished out.
> The
> > pitch lap was made on a base of some-sort of poured material, this is
> ok,
> > but there were still tiles from grinding under the pitch. GRRRRR. I was
> > back again this past friday, we switched to another pitch lap, this one
> is
> > better. Total actual polishing so far, 3.75 hours. The polish is all the
> > way to the edge, no hazy areas, just a nice smooth polish. Hard work but
> > fun. I plan on a total of at least 8 hours of polishing before taking a
> > look on the test stand.
> >
> > Until Then, Grind more and Enjoy the Sky
> >
> > Ed Witkowski
> > Woodbridge, VA
> >
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> 


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