Grinding your own mirror

bloodhound31 · #1 31-12-2006, 01:08 PM

Can anyone give me an idea of whats involved in making my own large aperture mirror (16 to 20 inch). I am toying with the idea of making a big scope for the observatory. I need to keep it short as I only have 1.5 metres from the centre of the dome to the walls. Cassegrain seems to be the way to go. I wonder if I can make large aperture mirror and tube, then adapt the existing fork mount to fit? That way I can keep my GPS go-to features.

Any indication of resources, price, availability of materials and places to get it done ( I live in Canberra), would be helpful.

Baz.

Barry's home-made observatory.

http://members.iinet.net.au/~armstead

dcnicholls · #2 31-12-2006, 05:03 PM

Baz,

If you've not ground a mirror before, starting with something as huge as a 16 or 20" would be like choosing Mt Everest to learn rock climbing. No easy task.

Mirror grinding is a vocation followed by numbers of amateurs, but many of them seem to spend all their time making telescopes and less actually using them

Track down Mel Bartels' website and have a read.

Another essential task is to join the ATM discussion group: http://www.atmlist.net/

Personally I'd explore buying a commercial mirror and building the telesccope around it.

Contact Peter Bobroff via the CAS and have a chat with him, too. He made a 20" Dob quite a while back.

DN
(also Canberra)

Blue Skies (Jacquie) · #3 01-01-2007, 01:14 AM

Make small one first, maybe 8". That'll show you what's involved and where all the traps are that you need to look out for in a big one, including the psychological hurdles! Rough grinding is easy but people often run out of steam half way through polishing, or going round in circles trying to get the figuring right. But if you really want to do it, then do it! Having a mentor whose been through it all before is also recommended, so contact your local society for help. And the ATM list is great for support, too (I am a silent lurker there).

CoombellKid · #4 01-01-2007, 08:36 AM

There is a club called Queensland Telescope Makers, I know they are a lil
far from you but it may not stop you becoming a member. They have a great
range of skills, and even do thier own forging to make the metal bits and
pieces. Which you can get access to as long as your a member.

Not sure if that was any help, but I thought I would post just in case.

regards,CS sunny days

bloodhound31 · #5 02-01-2007, 05:27 PM

Thank you gents! Most helpful...

Baz

cristian abarca · #6 02-01-2007, 06:55 PM

Just thought that I would add my 2 cents worth. Making mirrors is not an easy task and starting out with such a big mirror for a first attempt will probably end in dissapointment. most people usually start with a 6 or 8 inch mirror then proceed to larger sizes. I started with a 10 inch and have made 7 mirrors none larger than a ten inch. just now I'm contemplating making a 16 inch (if I can find a blank), and for making a cassegrain that is another story in itself. I wouldn't go there unless you were really keen (trust me I'm battling with one now). I'm not trying to sound negative about it but starting smaller is the only way to go. Just my opinion.

Regards cristian

Shawn · #7 02-01-2007, 07:05 PM

y first was a 16 Cass Baz, the primary is a doddle the secondary not so, suggest a newt for a start, But if you want a run down on what i did, It can be arranged, from procuring the glass to Aluminising, and yes I said aluminising..

rmcpb (Rob) · #8 02-01-2007, 07:10 PM

Making mirrors is part science, part engineering and part art, you have to get a feel for it.

Start with a smaller mirror and progress up in size would be my advice.

Cheers

Shawn · #9 02-01-2007, 08:12 PM

Quote:

Originally Posted by rmcpb

Making mirrors is part science, part engineering and part art, you have to get a feel for it.

Start with a smaller mirror and progress up in size would be my advice.

Cheers

rmcpb has said it too, practice on a small newt, silver the sucker if you have too, but I found that if you grind a mirror to maybe a half a wave, then silver it, it comes back at maybe 2 waves. Do you know how to do a foucoult test, Baz. In saying that silver does favour Red, Aluminum Blue. Each to there own..

S

Shawn · #10 02-01-2007, 08:19 PM

Baz , you say you are limited to swing room, tell me exactly what your swing room is, ?

S

bloodhound31 · #11 02-01-2007, 11:57 PM

S,

1.5 metres from the centre point in the dome to the inside skin of the dome.

Baz.

ok...u guys are scaring me now.....wanted to test the water as I will eventually upgrade the nexstar11 to a larger aperture scope. I thought grinding my own may be a cheaper alternative.... not interested in smaller at all..no sense going backwards.

Shawn · #12 03-01-2007, 12:14 AM

Quote:

Originally Posted by bloodhound31

S,

1.5 metres from the centre point in the dome to the inside skin of the dome.

Baz.

ok...u guys are scaring me now.....wanted to test the water as I will eventually upgrade the nexstar11 to a larger aperture scope. I thought grinding my own may be a cheaper alternative.... not interested in smaller at all..no sense going backwards.

It can be done Baz, but I wouldnt recomend it, Not a compound anyway..

Buying one at the end of day may well be cheaper in terms of time and money, but not satisfaction...

S

stephenmcnelley · #13 03-01-2007, 10:16 AM

I was part of a joint effort to grind a 6" newt mirror some time ago, ditto what the other lads have said here Baz- there is enough worry and fretting and labor involved with even a small mirror surface let alone a medium to larger one, but each to their own and that sure would be a super challenge in the long term if it can be afforded... though the likelyhood of imperfections rises exponentially with each extra bit of mirror area i believe...

CS
steve