Averted
professor emeritus
Reged: 01/26/05
Posts: 517
Loc: San Francisco
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How did this happen? 
Classic newbie mistake. I've been warned about this! But now my pitch lap tool is thoroughly engaged to my 12.5" mirror. I let it sit (while trying to press the lap) for too long. It dried up and now its STUCK! I've tried freezing the combo to no avail. I've considered pouring warm water on the tool after freezing it, and have considered trying to get water between the lap and mirror before freezing it again, hoping it might encourage the two to separate from each other. But of course I'm afraid of doing irreperable harm to my mirror.
Any suggestions are welcome! (especially those that have been tried) 
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Dave
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-'lil Ranger, Orion ST80
-Criterion RV-6, Criterion 4"
-Intes M503
-Homebrewed 12.5 needing an OTA
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MMICKELS
Aluminum Knight
Reged: 01/20/04
Posts: 25198
Loc: The Land of Shake and Bake
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Dave, I would let it soak in warm soapy water after the mirror has reached room temperature. I have never made a mirror though, and this is just a suggestion.
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Mark
"The only thing wrong with immortality is that it tends to go on forever."
Herb Caen
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Stefan Rostyne
scholastic sledgehammer
Reged: 10/19/04
Posts: 940
Loc: Assenede, Belgium
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Put the 'unit' vertical and let some water run between the channels in the lap. You may add some dishwasher detergent. You can see the squares get wet through the glass. Put it horizontal again, wait a few minutes and then gently start trying making strokes. It will get loose after some minutes.
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Stefan Van de Rostijne
4.5" F4.5 newt 5°widefield/finderscope
8" f/5.6 travel dob
old 12.5" F5 dob (used to look better...)
30 cm f/30 Classic Cassegrain (polishing primary)
23" f/4 dob project
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waynet
professor emeritus
Reged: 04/20/05
Posts: 632
Loc: Oklahoma, USA
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I consider myself an expert in this area (I am a pretty slow learner). Lukewarm water works every time for me. After soaking a while you should be able to gently slide them apart. (Sometimes I let it soak for 15 minutes).
good luck,
wayne
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Averted
professor emeritus
Reged: 01/26/05
Posts: 517
Loc: San Francisco
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Quote:
Put the 'unit' vertical and let some water run between the channels in the lap. You may add some dishwasher detergent. You can see the squares get wet through the glass. Put it horizontal again, wait a few minutes and then gently start trying making strokes. It will get loose after some minutes.
o.k. now for the confession. There are no channels!  The lap was recently poured and i hadn't had a chance to cut the channels yet, thus perhaps casuing the two to glue together so quickly. I certainly hope i i don't have an irrerperable mess on my hands, but I'm not sure if soaking it will work for this reason (though I'll give it a try).
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Dave
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-'lil Ranger, Orion ST80
-Criterion RV-6, Criterion 4"
-Intes M503
-Homebrewed 12.5 needing an OTA
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lukasik
scholastic sledgehammer
Reged: 10/11/05
Posts: 876
Loc: Lawrenceville, Georgia
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Dave, I did exactly this same thing - no channels in the lap and stuck like glue (especially in the dead center). I tried over the course of a day soaking, soap, turpentine, a hose and more to no avail. I finally did something really stupid that I won't go into (which still didn't separate the mirror and tool). What did get them apart (but ruined the lap - you can always repour it) was to shine a sunlamp through the back of the mirror for several hours. The lamp wasn't close enough to heat the mirror rapidly - be careful you don't want fast heating or you could crack your mirror. Eventually the top surface of the pitch just about melted and they could be slowly separated. This worked since the back surface of my blank happened to be flat, clear, and polished allowing the heat energy of the light through to the darker pitch. If your blank is ground on the back this might not work at all. Perhaps you could very slowly heat the whole thing in water like boiling a frog.
Good luck - remember: macho does not apply here, think it through.
Best regards,
Bob
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waynet
professor emeritus
Reged: 04/20/05
Posts: 632
Loc: Oklahoma, USA
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Well, I have been down this road too (and I imagine it is pretty well traveled). The pitch on my first mirror was so soft that the first time I pressed all the channels closed and it stuck.
I tried all kinds of things, but ultimately got the tool and mirror warm enough that the pitch got soft and I was able to gently slide them apart, however, in that case some of the pitch was attached to the mirror so I had a messy clean-up, but no harm was done to mirror or tool. (I assume the safe return to clean mirror and tool is what were are after here, and not preserving the lap).
So I would try a warm soak, then a warmer soak and so on until I could slide them apart gently. (Soap wouldn't hurt.)
I would start at 100F or 40C and go up (slowly) from there.
Good luck.
wayne
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John Vogt
member
Reged: 10/26/05
Posts: 33
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You can also try using a set of wood clamps or pipe clamps to separate the pieces. Put the lip of one clamp on the edge of the tool and the other on the edge of the mirror. If the clamps are metal be sure to use wood between the tool/mirror and clamp so you don't break anything. Tighten the clamp a bit, wait a while and tighten it some more. Let the force of the clamps do the work over time. I've had 100% success with this on lap/mirrors up to 32". You just have to be patient.
BTW, this method was originally shown in ATM 1.
John
Edited by John Vogt (10/28/05 08:48 PM)
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Averted
professor emeritus
Reged: 01/26/05
Posts: 517
Loc: San Francisco
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Thanks fellas.
Since the tool is solid, I think I will try the warm water approach. Seems the safest. heating the lap to goo seems the right approach.
Say I wasn't as concerend about the tool as I am of the mirror. Any reason I wouldn't try heating up the back surface of the tool with a hotplate?
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Dave
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-'lil Ranger, Orion ST80
-Criterion RV-6, Criterion 4"
-Intes M503
-Homebrewed 12.5 needing an OTA
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Lawrence Sayre
Post Laureate
Reged: 10/16/04
Posts: 3708
Loc: N.E. Ohio
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I 2nd John Vogt's suggestion above. I've done this many times, including on the big 30" mirror. If done properly, no harm will come from it, and they will separate.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Averted
professor emeritus
Reged: 01/26/05
Posts: 517
Loc: San Francisco
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Quote:
You can also try using a set of wood clamps or pipe clamps to separate the pieces. Put the lip of one clamp on the edge of the tool and the other on the edge of the mirror. If the clamps are metal be sure to use wood between the tool/mirror and clamp so you don't break anything. Tighten the clamp a bit, wait a while and tighten it some more. Let the force of the clamps do the work over time. I've had 100 success with this on lap/mirrors up to 32". You just have to be patient.
BTW, this method was originally shown in ATM 1.
John
Interesting. I have ATM 1--I'll have to look it up.
Thanks much
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Dave
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-'lil Ranger, Orion ST80
-Criterion RV-6, Criterion 4"
-Intes M503
-Homebrewed 12.5 needing an OTA
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1084
Loc: Sin-sin-atti
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Dave,
I've never seen freezing fail to work. Did you leave them in the freezer overnight or many hours? If so try John's method after freezing. To avoid this from happening again use a piece of plastic garbage bag between them for pressing.
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Ed Jones
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Averted
professor emeritus
Reged: 01/26/05
Posts: 517
Loc: San Francisco
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Ed,
yes I did leave it overnight. It was frozen when I retrieved it!
Right now it is on a table with a vice clamp attached. it appears to be moving very slowly. I went fo rthis method because it might be posible to save the lap. I'll let everyone know how it turns out!
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Dave
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-'lil Ranger, Orion ST80
-Criterion RV-6, Criterion 4"
-Intes M503
-Homebrewed 12.5 needing an OTA
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Averted
professor emeritus
Reged: 01/26/05
Posts: 517
Loc: San Francisco
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It worked! Thanks John! this thread should be put in the archives for future reference, me thinks!
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Dave
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-'lil Ranger, Orion ST80
-Criterion RV-6, Criterion 4"
-Intes M503
-Homebrewed 12.5 needing an OTA
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Averted
professor emeritus
Reged: 01/26/05
Posts: 517
Loc: San Francisco
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Ed. Yes. Lesson learned!
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Dave
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-'lil Ranger, Orion ST80
-Criterion RV-6, Criterion 4"
-Intes M503
-Homebrewed 12.5 needing an OTA
Edited by Averted (10/28/05 12:13 AM)
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lukasik
scholastic sledgehammer
Reged: 10/11/05
Posts: 876
Loc: Lawrenceville, Georgia
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Dave, I'm happy to hear that you got them apart with no harm done. Congratulations!
Regards,
Bob
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John Vogt
member
Reged: 10/26/05
Posts: 33
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Your welcome. Glad to read that this worked for you although it does tend to make one kinda nervous while applying the pressure, esp. on a big lap. 
OK, now lets finish it. 
John
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MMICKELS
Aluminum Knight
Reged: 01/20/04
Posts: 25198
Loc: The Land of Shake and Bake
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Quote:
It worked! Thanks John! this thread should be put in the archives for future reference, me thinks!
Dave, I've added a link to this thread in the best of ATM thread. Good suggestion, thanks! 
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Mark
"The only thing wrong with immortality is that it tends to go on forever."
Herb Caen
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Scott Milligan
super member
Reged: 09/08/05
Posts: 112
Loc: MA
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Averted:
Since this recently happened to me while polishing a $10,000 32" diameter Lighweighted blank, and since no one else has posted the solution that eventually worked for me, I'll give you one more way out of this fix (try the others first).
Make six wooden wedges with the wedge taper at about 10-15 degrees, and the thin edge of the taper thinner than the pitch lap thickness. Using a chisel or other suitable tool, create six pockets at the edge of the lap by chiselling out the pitch (taking care not to scratch the optical surface if possible). Insert the 6 wedges into the chiseled pockets, and sequentially tap the back side of the wedges in towards the center of the hated mess, until separation occurs. I had to do this three times before the 32" was finished, and (praise to the gods) did not cause any harm to the mirror.
Scott Milligan
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HandyAndy
sage
Reged: 01/11/08
Posts: 412
Loc: West Midlands and around
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Hi,
Frank Hourigan advised me to use Baby Oil rather than water to mix the polishing compound with. It does not evaporate and as its a lubricant you have less chance of the lap sticking.
It is hard getting fine powder to mix well with water anyway. I was motorcycling when I was polishing my first mirror making attempt and the vibration on my rear rack produced a lovely mousse in the container. You could try taping the mixture to a spin dryer.
Did you coat the mirror with polishing compound before putting the new pitched lap on it? Tom Collier who managed the mirror making would do that and then work the new lap on it to shape. He then cut the grooves out. Before storage he would put some more compound onto the mirror.
Cheers. Andrew.
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Monarch 8x42, Zeiss 10x50 WA
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