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First time mirror grinding...

Started by Wolfstar, 07/07/2010 09:33AM
Posted 07/07/2010 09:33AM Opening Post
I am going to give mirror grinding a shot with a 4.25 in blank and tool purchased from a gentleman here on Amart, any suggestions (besides reading lots of books!) from veterans out there? I figure this size would be forgiving to start with, any suggestions on f ratio etc?

Thanks and Clear Skies

It is what it is...
Posted 07/07/2010 10:32AM | Edited 07/07/2010 10:33AM #1
Tony Aguire said:

I am going to give mirror grinding a shot with a 4.25 in blank and tool purchased from a gentleman here on Amart, any suggestions (besides reading lots of books!) from veterans out there? I figure this size would be forgiving to start with, any suggestions on f ratio etc?

Thanks and Clear Skies

1. KEEP IT CLEAN.

and...

2. Build/buy the best Focault Tester you can...

Oh...and whichever books you have, get a copy of Sam Brown's _All About Telescopes_ to go with 'em.

In general, mirror grinding, polishing, and figuring is FAR, FAR easier than you may believe or may have been led to believe.

wink

Uncle Rod

Time on your hands?
Waste it with Uncle Rod's Astro Blog!

http://uncle-rods.blogspot.com/
Posted 07/07/2010 12:23PM #2
Good luck, Tony. This is one of those things I hope to do 'one day'.

[COLOR="Blue"]Darian Rachal[/COLOR]
Posted 07/08/2010 04:00PM #3

Congrats and welcome to the mirror makers world. You will soon find that it can be quite rewarding and frustrating....frustration comes when you become anxious...remember nothing happens fast in making a mirror...you are grinding away glass and that can take some time...when when you get started you may find that grinding your mirror to to get the right sagitta(curve)..you may go faster then you think. The F ratio is up to you and grinding yout tool against your blank will determine this. I suggst you begin with either f/6 or f/8...the faster the ratio the easier it will be to figure and actually grind...less material to remove in the sphere stages...and less figuring in the final stages. Do lots of reading....make or acuire a Foucault tester...and learn how to use it.

Go to Stellefane.com and scoll through their site and you will find the mirror making section....read it till your eyes bleed(just joking) grin

Get a suitable surface to grind on and preferably somthing you can *walk around*...get some *carpet backing* for a backing to place your blank on while grinding and polishing.

You have lots to do...but it will exciting and rewarding.

Keep us posted and let us know if you need any advice.

Rob


Tony Aguire said:

I am going to give mirror grinding a shot with a 4.25 in blank and tool purchased from a gentleman here on Amart, any suggestions (besides reading lots of books!) from veterans out there? I figure this size would be forgiving to start with, any suggestions on f ratio etc?

Thanks and Clear Skies

Eternity is a long time to be wrong.....so accept Jesus as your Savior.
Posted 07/14/2010 12:48PM #4
All good advice above, I would only add that I think a spherometer is helpful(but for that size I'm not sure). Gordon Waite has good instructions on how to make one on youtube.

Also, if you plan to build the foucault tester, build it with a platform or something stable to attach a digital camera too, to take pics to show the guru's online in case you need guidance.
Posted 07/14/2010 01:18PM #5
Rod has it right. In small sizes, this is a lot eaier than some folks would make it out to be. You can finish a 4.25 easily in a weekend. (in a day once you've been through the process)

Aim for an F8-F10 and you won't have to parabolize it. If you are out by a few inches on the targetted focal length it won't matter until it's time to make the tube.

When you get bored with the longer scope, regrind the mirror down to an F5-F6 and have a go at parabolizing.

Have fun but be aware, it's addictive!

dan