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How much time to grind

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#1 Nebulae

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Posted 10 January 2013 - 05:52 AM

Hello i have already started to grind 6.5 inch 1200mm mirror. i would like to know how much time does it take to grind to 1200mm focal length and how much carbo 80 is needed?

#2 gpelf

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Posted 10 January 2013 - 07:45 AM

Nebulae, Hi,

1/2lb. should be more than enough for a 6", You will find as you go smaller in grit size the "WET" will last much longer. As far as the time it really depend on a lot of factors (Grinding style, pressure, E.T.C) I have found one good habit to have is not to go to fast with the grind, especially at finer grits and polishing.

Keep us informed!!!!

#3 Nebulae

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Posted 10 January 2013 - 10:36 AM

sure i will inform how much time it took. i will post my review here

#4 Ajohn

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Posted 10 January 2013 - 12:09 PM

My 1st mirror used a pyrex blank and a plate glass tool. Some of the low expansion blanks grind very slowly - the glass tool didn't though. I used a lot more coarse grit than expected.

John

#5 danjones

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Posted 10 January 2013 - 11:48 PM

just take your time. work when you can. be careful of glass dust, always work wet. take your time so you can be precise. ask the forum for advice with each step if needed, watch videos, and update your post often so others can see your progress to able to help you better. you can do it. good luck.

#6 Nebulae

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Posted 11 January 2013 - 04:47 AM

friend today i had a bad day, my 12 yrs old son broke the primary mirror 6.5". It got slipped from his hand.
i dont have any words to say. i lost all my hard labor,time and carbo #80 and money too.

For me it took 4 hrs to grind and focal length was exactly 1200mm. I used two blanks of plate glass. Mirror was 19mm thick and tool was 12mm thick.
Pressure was neither too hard nor too light, it was medium.

Finally i again need two blanks of glass

#7 ccaissie

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Posted 12 January 2013 - 01:06 PM

Ouch!

I have used a curved tool on a fresh blank before, so maybe some cost and labor are not lost.

Persevere!

C

#8 Gary Fuchs

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Posted 12 January 2013 - 01:35 PM

Sorry to hear that.
I hope you can obtain more glass and supplies; and that you won't be discouraged from letting your son continue to be involved.
The tool should be reuseable.

Gary

#9 ed_turco

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Posted 14 January 2013 - 08:39 PM

Please note that I have deleted a comment here and moved it to The Off-Topic Observatory forum. I have a serious issue that I wished to discuss and anyone interested can find it there.


Ed

#10 Pinbout

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Posted 14 January 2013 - 10:30 PM

sent you a pm.

#11 danjones

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Posted 14 January 2013 - 11:59 PM

Just some freindly info Nebulae, I do have 2 6 inch by 1 inch thick blanks that I trepanned myself for sale on the classifieds. Just a few bucks for them plus shipping. I don't need them. These were practice while I learned how to make them. They are decent blanks. You can find the ad if interested. I'm actually grinding a 10 inch now made from that same chunk of glass which is progressing nicely. Have a look and if you want them, just messege me. Good luck.

#12 danjones

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Posted 15 January 2013 - 12:02 AM

Here's a pic. They are dark tinted, but have not provided me any issues at all. There is some scratching from the grit and cutter I used to make them, but shouldn't be any problem for making a mirror. check it out if you like.

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