Re: [ATM] TDE (That Darned Edge)

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

Jerry:

I have two of the 22" F/4.5 blanks left for $900 each. Polishing and
figuring one of these will be a challenge. Especially for your machine.
Gearing it down will make a big difference if you are going to make it pull
a full size lap. Can you post a picture of your machine? 

James

James Mulherin
Optical Mechanics, Inc.
jcmulherin@opticalmechanics.com
www.opticalmechanics.com
Tel: (319) 351-3960
Fax: (319) 351-3943
> -----Original Message-----
> From: Jerry [mailto:wa4guu@verizon.net]
> Sent: Thursday, April 27, 2006 9:49 PM
> To: 'jcmulherin'
> Subject: RE: [ATM] TDE (That Darned Edge)
> 
> I think the ratios are good but I will modify it to go slower to match
> your
> speeds better. My slowest speed gets down in the neighborhood you are
> speaking of but I would like a range of choices around that speed.
> 
> In hand figuring that is something that I learned makes a fine smoothness
> in
> the surface texture.  I work as slow as I can stand. Some people would
> have
> to take my pulse to see if I had died while I am figuring.
> 
> I am going to put another reduction to make the entire speed range in the
> very slow to just slow.  That will give more leverage to move the laps. I
> have one motor running both turntable and stroke. I might add a separate
> motor for stroke.
> 
> My brother and I built this machine about 30 years ago. Its been used for
> grinding and polishing a bunch of lenses and mirrors but for figuring I
> have
> done hand work since I knew there was something I didn't know about
> machine
> figuring.
> 
> We made this thing with the idea 20" would be a size beyond which we would
> never do.  That was considered beyond amateurs back then. I like the
> machine
> but I will have to modify it to do larger. But that wouldn't really be
> difficult.
> 
> My brother and I have another machine given us by the family of a deceased
> ATM that will do larger without modification. I will use that if necessary
> but I like our own machine more.
> 
> There is no chance what-so-ever I would turn down your assistance, unless
> I
> don't have a pulse.
> 
> And I have discussed this with my wife and she knows I have to take the
> opportunity for a blank right in the size range I want and just the right
> thickness.  I said I wanted something between 20 and 24 inches and 2
> inches
> thick. 22 inches is dead in the middle of what I want.
> 
> How much do you want for one of those 22 inch blanks, if you still have
> one.
> I will find the money.
> 
> Jerry
> 
> 
> 
> -----Original Message-----
> From: jcmulherin [mailto:jcmulherin@opticalmechanics.com]
> Sent: Thursday, April 27, 2006 10:19 PM
> To: 'Jerry'
> Subject: RE: [ATM] TDE (That Darned Edge)
> 
> Jerry:
> 
> It's odd, but we've had to modify most of the polishing machines we've
> purchased to get the slow speeds we like to work with. Most machines run
> too
> fast, or don't have the grunt to pull a lap when you run them slow. What
> speed ranges do you have available on your spindle and eccentric?
> 
> Let me know if you would like some guidance on your next project. I
> wouldn't
> mind doing another on-line figuring session...
> 
> James
> 
> James Mulherin
> Optical Mechanics, Inc.
> jcmulherin@opticalmechanics.com
> www.opticalmechanics.com
> Tel: (319) 351-3960
> Fax: (319) 351-3943
> 
> > -----Original Message-----
> > From: Jerry [mailto:wa4guu@verizon.net]
> > Sent: Thursday, April 27, 2006 5:57 PM
> > To: 'jcmulherin'
> > Subject: RE: [ATM] TDE (That Darned Edge)
> >
> > Thanks James...
> > Yes the last I looked it is still on the ATM Free. That was about a week
> > ago.  And I had already saved a copy anyway. I would not have taken a
> > chance
> > of that being lost. There are few pros' that will give detailed figuring
> > methods as you have, or even skilled amateurs. It may just be that they
> > think it is too difficult to explain. So thanks for the lesson.
> >
> > I tried my hand at machine figuring a 12.5 many years ago but was doing
> it
> > wrong. So I finished by hand. I watched the progress on that 18 mirror
> > closely and tucked it away to be used at the right time. I think I
> > understood the procedure pretty well. Well enough to get a good start.
> >
> > Steve Koehler sent me some test images of an 18 inch and I've looked at
> > the
> > OMI test result of your mirrors many times. Mighty fine.
> >
> > Happy to see you came through the storms ok.
> > Jerry
> >
> >
> >
> > -----Original Message-----
> > From: jcmulherin [mailto:jcmulherin@opticalmechanics.com]
> > Sent: Thursday, April 27, 2006 4:18 PM
> > To: 'Jerry'; 'ATM List'
> > Subject: RE: [ATM] TDE (That Darned Edge)
> >
> > Hi Jerry:
> >
> > We have two temp settings in the shop. In the winter we keep the
> > thermostat
> > at 70 and use one teaspoon of linseed oil per kilo of Gugolz 64. We use
> > this
> > formulation for polishing and figuring.
> >
> > In the summer we try to keep the temp at 75 and use straight Gugolz for
> > polishing and figuring.
> >
> > Pitch thickness is also a factor. A lap with a thick layer of pitch will
> > act
> > softer than a lap with a thin layer. We polish a number of mirrors with
> a
> > lap but monitor thickness between mirrors. As you know, the pitch gets
> > thinner as the channels flow shut and you re-trim them. For larger
> mirrors
> > (12.5" diameter and up) we pour a full size lap .75" thick and work it
> > until
> > it's about 3/8" thick. Then we re-pour it. We get about 10 mirrors out
> of
> > one lap. For smaller laps, and in particular figuring laps (4" to 10"
> > diameter) we start with 5/8" thickness and run till the pitch is 3/8"
> > thin.
> > We figure about 5 mirrors with a set of figuring laps before re-pouring.
> >
> > We do most of our polishing with full size laps. We set the machine to
> > make
> > a normal 1/3 wide stroke with 1/6 overhang at each end of the stoke. The
> > table speed is about 5 rpm and the stroke speed is about three times
> that.
> > Assuming your lap is making good contact this technique will reliably
> > produce a decent sphere with a clean edge. We'll typically polish for
> > about
> > 10 hours of machine time to complete the polish.
> >
> > I haven't looked in a whit to see if John's a8" figuring project is
> still
> > on
> > the ATM_free list. If it isn't I'll compile something and post it to our
> > web
> > site. Let me know if you can't find it.
> >
> > James
> >
> > James Mulherin
> > Optical Mechanics, Inc.
> > jcmulherin@opticalmechanics.com
> > www.opticalmechanics.com
> > Tel: (319) 351-3960
> > Fax: (319) 351-3943
> >


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