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  #1  
Old 15-04-2018, 09:40 PM
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Lognic04 (Logan)
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Making a 10" Dob

Hi all,
I have finally decided to take the plunge into mirror making! Going old school!
I am planning to grind my own 10 inch (250mm) f/6 (1500mm FL) Mirror to go into a 10 inch dobsonian tube that has been sitting unused.
Picking up the materials on Saturday, and am going to get help from the ASV all the way
This is my first time mrror making! :O
Going to regularly update this thread on the progress!

Last edited by Lognic04; 16-04-2018 at 08:00 AM.
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  #2  
Old 15-04-2018, 10:59 PM
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Atmos (Colin)
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Awesome!
This is one of the things to do on my bucket list.
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  #3  
Old 16-04-2018, 07:59 AM
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Quote:
Originally Posted by Atmos View Post
Awesome!
This is one of the things to do on my bucket list.
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  #4  
Old 16-04-2018, 08:01 PM
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Few questions:
Is there a way to measure my curvature relatively accurately without a spherometer?
I am seeing different methods of testing the mirror, is a ronchi/focault combination fine? Or is it better to map it with a PC?
Thanks!
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  #5  
Old 16-04-2018, 10:43 PM
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OzEclipse (Joe Cali)
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Hi Logan,

Good on you. I made my own mirror for my first scope when I was 15.

While you are grinding the easy way is to swish some water over the ground surface and focus the sun. I had a long wooden stick 2m long. I attached a piece of white card to one end and marked distance at the other end. You can use 100mm markers for the longer lengths then drop down to 10mm markers near your target focal length. Take the mirror outside on a sunny day, slosh water over the surface and focus the sun on the white card, read the focal length off your distance markers.

A 10" f6 has a 2.6mm deep sagitta or curve. If you don't have the sun, you can lay a straight edge across the whole diameter of the mirror. Then compare the centre depth to a depth marker like a 2.5mm drill.

You only use these methods when you are rough grinding. Get the focal length a couple of inches longer than you want by the end of the 80 grit grind. The fine grind will take the rest off. By the time you get to Ronchi or Foucault test (not Focault) you are polishing and the focal length won't change much during polishing. You can however use these tests to determine the focal length accurately.

Have fun mate.

Joe

Last edited by OzEclipse; 16-04-2018 at 11:11 PM.
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  #6  
Old 17-04-2018, 06:56 AM
Baza (Barry)
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Logan
there is a mirror making thread with lots of info, also have a look at https://stellafane.org/misc/links.html#Equatorial and http://www.bbastrodesigns.com/JoyOfMirrorMaking/ both have heaps of info burt you might have to dig a little.
http://www.mirror-maker.com/
awaiting the progress reports. Barry

Last edited by Baza; 17-04-2018 at 06:57 AM. Reason: another link
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  #7  
Old 17-04-2018, 08:05 AM
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Lognic04 (Logan)
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Quote:
Originally Posted by OzEclipse View Post
Hi Logan,

Good on you. I made my own mirror for my first scope when I was 15.

While you are grinding the easy way is to swish some water over the ground surface and focus the sun. I had a long wooden stick 2m long. I attached a piece of white card to one end and marked distance at the other end. You can use 100mm markers for the longer lengths then drop down to 10mm markers near your target focal length. Take the mirror outside on a sunny day, slosh water over the surface and focus the sun on the white card, read the focal length off your distance markers.

A 10" f6 has a 2.6mm deep sagitta or curve. If you don't have the sun, you can lay a straight edge across the whole diameter of the mirror. Then compare the centre depth to a depth marker like a 2.5mm drill.

You only use these methods when you are rough grinding. Get the focal length a couple of inches longer than you want by the end of the 80 grit grind. The fine grind will take the rest off. By the time you get to Ronchi or Foucault test (not Focault) you are polishing and the focal length won't change much during polishing. You can however use these tests to determine the focal length accurately.

Have fun mate.

Joe
Thanks for that Joe! I will definitely be using these techniques!

Quote:
Originally Posted by Baza View Post
Logan
there is a mirror making thread with lots of info, also have a look at https://stellafane.org/misc/links.html#Equatorial and http://www.bbastrodesigns.com/JoyOfMirrorMaking/ both have heaps of info burt you might have to dig a little.
http://www.mirror-maker.com/
awaiting the progress reports. Barry
Thanks Barry!

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  #8  
Old 17-04-2018, 10:55 PM
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Another newbie question, what should I make my tile tool with? Does it need to be curved?
Thanks!

Last edited by Lognic04; 18-04-2018 at 07:08 AM.
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  #9  
Old 20-04-2018, 06:33 AM
Baza (Barry)
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double post
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  #10  
Old 20-04-2018, 06:34 AM
Baza (Barry)
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you need tiles of the same hardness all the way through. non glazed exterior tiles seem to work. they can be stuck to dental plaster. you will need to waterproof plaster of paris if you use that. details and photos on stellafane & numerous other sites.
It will curve with correct use.
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  #11  
Old 21-04-2018, 09:06 PM
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DAY 1! 2 hours work - flattening the back of the blank with 80 grit, almost done. Lot of fun so far!
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  #12  
Old 22-04-2018, 10:13 AM
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Good on you Logan should be good experience before you tackle a 20 inch f4
Good luck ( remember the harder you work the more good luck you get) and post often.
Alex
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  #13  
Old 22-04-2018, 10:15 AM
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And you know we are all expecting a full length movie.
Alex
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  #14  
Old 22-04-2018, 02:55 PM
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Are you hand grinding?
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  #15  
Old 25-04-2018, 11:03 AM
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Lognic04 (Logan)
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Hehe thanks Alex. I am hand grinding.
Look forward to that video!
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