Advice for figuring a f/4.6 mirror

[Garyh]

Hi guys,
Well my 8" f/4.6 mirror is now all but polished out and just needs some slight correction for a small TDE before I try to parabolise the mirror.
My 6" mirror was slower and therefore easier to do. So before I attempt figuring does anyone have advice that might be helpful?
Would I stick with my full size lap for this? and would I need to modify the figuring stroke? and how long for a first session?
Most info I find seem more related to a slower mirror or large mirrors using small figuring laps..
All info/advice will be very appreciated....:thumbsup:
cheers Gary

[DaveGee]

Hi Gary,

I've recently finished a 10"f4. thew! fast mirrors are sure harder to figure!

I used a 60% tool, working TOT. I started out with a 30 minute session of W strokes concentrating mainly CoC and the closer I got to the paraboloid, the shorter the time. The penultimate last step was only once around of no more than 2 minutes and the very last session was 2 minutes with my thumb dipped in CeOx to deepen the very centre.

figure-test-figure-test-fig..... you get the idea!!!!

It was an experience not to be missed IMHO.

[Garyh]

Hey thanks Dave! a 10" f/4 would be hard work! Did you get a great figure in the end?
I will try a full size lap first and see how it goes..
Knocked the TDE off last night and have now got very close to a sphere. Just have a slight depression in the centre. As a rough guess I have a 1/6-1/8 wave sphere.
Might try a 20min session at parabolising and then test. I think the slight hole in the centre will work in my favor! :thumbsup:
I shall start a new thread about this and my progress!
cheers Gary

[madtuna]

as odd as it sounds..I'd kill to watch one of you guys at work on your mirrors.
I find it facinating and one day may work up the balls to have a go myself lol

[DaveGee]

Well you don't need to go that far...:rofl:

There are heaps of movies of people making mirrors on YouTube. Here is a link to Francis J O'Reilly's videos... http://www.youtube.com/user/foreilly1958

There is a mountain of info about the art and you can spend hours (years) reading, watching and wondering but 30 seconds with abrasive on that first mirror will teach you more.

[madtuna]

thanks mate :thumbsup:
will take a browse. am very tempted to give it a go

[DaveGee]

It wasn't too bad. A 1/20th wave optic it ain't but the numbers came up OK. It'll be good enough.

[pelu]

I do not like to parabolise with small or modified tools . Is
possible that with mirrors of 16" or more can be more comfortable a 2/3 tool but up to 12" I always parabolize my mirrors with the Texereau book (how to make a telescope) open in front of my eyes. :scared2: