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storing polishing lap o/n

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#1 macleod

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Posted 12 December 2018 - 03:13 AM

Made a new polishing lap for a 10inch F3.3  x 3/4 inch mirror, Gugolz 64. Got a really good press contact , but cutting channels caused lot of chipping. This is a new tub of pitch, working at room temp of 64- 68deg F. Pitch seems very hard to fingernail test, and seems to shatter very easily when trimming, but will see if channels close with cold pressing.

My question is , can I store the mirror and lap together overnight, lap on top ( about 4lbs )separated by thick plastic bag stretched over mirror? A cold press really. I know I will have to touch up channels before work in morning , do another cold press before polishing, but I will not usually cold press so aggressively, but I am breaking in my new lap.Otherwise how do you keep laps o/n - in a dish room temp water maybe? Thank you, MACLEOD.



#2 Benach

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Posted 12 December 2018 - 04:00 AM

I keep my laps always in a small fridge.


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#3 Billyboy78

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Posted 12 December 2018 - 04:25 AM

Leave out the thick plastic bag. Just spread CO on the mirror, place the tool on top with no weights and drape a damp towel over the top. Perfect contact the next morning. It can be left for a night or two but dont let it dry out.


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#4 dave brock

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Posted 12 December 2018 - 05:08 AM

☝️ What he said.
I've left laps on mirrors for a few days many times without any issues. Just don't let it dry out.

Edited by dave brock, 12 December 2018 - 05:08 AM.

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#5 dogbiscuit

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Posted 12 December 2018 - 05:36 AM

I don't mind much when they dry out.  I've learned how to separate them without much difficulty, and without heating or cooling.



#6 Pinbout

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Posted 12 December 2018 - 06:45 AM

I do not store pressing 

 

I warm press by soak both mirror and lap.

 

I use an iron to open channels.   

 

I don’t like leaving cerox on the glass.


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#7 ckh

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Posted 12 December 2018 - 10:22 AM

Thin plastic grocery bags work well without cerox.  Perhaps not perfect contact, but close enough to cold press for a short period.

 

Carl



#8 DAVIDG

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Posted 12 December 2018 - 10:53 AM

I do not store pressing 

 

I warm press by soak both mirror and lap.

 

I use an iron to open channels.   

 

I don’t like leaving cerox on the glass.

 I agree with Danny. It doesn't take long to warm press  a lap back into contact. If you leave the mirror on the lap, the channels will close up and you risk getting the mirror stuck to the lap. If that happens  you can damage the lap getting the mirror free. 

   The secret to mirror making is understand how the contact  of the lap effects the figuring. I have seen ATMs fight for years trying to figure a mirror because they don't understand this concept. If you want a spherical surface, that means that lap must wear the optical surface uniformly. That requires uniform contact and that require equal area of contact. This means the facets and the channels need to be uniform in size across the whole lap. A small difference will lead to zones. Once you understand this you'll have no problems making perfectly spherical surface. When it comes to figuring a parabola, the classic W stroke works on the assumption that your starting with a spherical surface and have a lap that has uniform contact. The stroke causes control wear of the surface to turn into a parabola. If you don't have a lap with uniform contact, the W stroke doesn't work and you most likely dig a hole.

   So if things are working and you stop and let the mirror sit on the lap, the lap is changing shape, ie the channel are start to closeup. So try to pick up were you left off and the next time you  test, the figure as got away from you and  your wondering  what is going on ? !  So what I do is just cover the lap with food wrap, and when I start up again do a mild warm press and make sure that the channels are still open to same width all across the lap. I can control the figure and I don't get surprised the next time I test it.

 

                      - Dave 


Edited by DAVIDG, 12 December 2018 - 04:20 PM.


#9 ckh

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Posted 12 December 2018 - 01:08 PM

I should add that I stopped storing my mirror on the lap overnight. It makes lap rework more frequent.

 

If you need to store a lap for a long time, it might be good to refrigerate it.  I left mine out for over a week (at about 80 degress during the day) and was amazed how far out of good contact it got with no weight at all on it. It could actually see that the lap was misshapen.



#10 ed_turco

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Posted 12 December 2018 - 01:27 PM

I keep my laps always in a small fridge.

I keep my mirror/lap combination is a large pan of water -- covered.  Facilitates contact; it is ready to go after any length of time.


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#11 Oregon-raybender

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Posted 12 December 2018 - 03:47 PM

Liquid (clear) soap and plastic cover or bag works fine. No contact needed, Pressing if re-working in a few days. Warm press before restarting (soap or compound) . Keep in a cool place, <68 degrees. Do not keep in frig or freezer, the pitch can fracker off the tool. 

 

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#12 macleod

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Posted 12 December 2018 - 03:54 PM

Thank you all for your great info. DavidG - from all I,ve read your advice on the lap contact etc makes perfect sense, especially to avoid polishing zones into surface when using a rough lap. Danny - I,ve watched many of your videos , they,re a great help. For a warm press, how hot should water be? Approx ! Do you press , open channels, and leave until gets back to room temp before polishing ? I thought using a warm lap/tool combo to polish caused problems. Thought all working should be at one even temp, especially with thin float glass. Pyrex or Quartz  probably ok. Anyway , great advice all round, thank you all. MACLEOD



#13 Benach

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Posted 12 December 2018 - 04:28 PM

Ed Turco: Will that a try when I will be optics making on a regular basis again, probably within a few months from now. Ah, looking forward to it. The ideal way for me to relax... Just let the optics become what they should become. Slowly but surely you get what you were after. Love it.




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