A superb result, Raymond. Well done.
Time to check that Royce 10" for a possible refigure?
Dave
Haha yeah. I did have a look at it with the ronchi screen. It has something funky going on at about 75-80% I'll have to take a pic of it, it looks more like a patch of bad roughness than anything else. It was a few months ago i looked at it. It produces really nice images and views so i can't see me doing anything to it. My next project other than a scope for this mirror is a vacuum chamber.
I had a good compare between the 10" Royce and this 18" mirror tonight. I couldn't really see anything between them other than Jupiter's moons were smaller in the 18", the seeing wasn't that great but i would give the edge for detail to the uncoated 18". I need to make a real scope for it as collimation is inconsistent with my test Dob scope i've made for it.
+1 Excellent result. Just goes to show that an ATMer can grind, polish, and successfully figure a large aperture mirror to a high degree of accuracy "straight out of the blocks". There is so much help out there on the internet, for anyone who has the determination, and patience, to take on such a project. Again super effort.
bit of a quandary really. My 14"f5.1 and 25"f4.7 (Also have 25"f5 and f5.3 mirrors, [need varying amounts of figuring to finish off properly]) use 3.1"ma and 4" ma secondaries sourced from Hubble Optics, (reasonably priced, and work quite well).
For a 33"f4, going to need at least a 6 1/2"ma (for good size fif). Looking around the "net", looks like US$1000 HO to US$1350 Astro Systems + Freight + GST etc, so wouldn't have much change out of NZD$2000, so way out of my budget, (want to build entire scope for less than NZD$2000).
So looking at my options, and seems only to be the one, make it myself. Got plenty of thick glass lying around (still 1/2 ton), included are a number of 12.2"/12.6" diameter blanks 1 3/8"/1 1/2" thickness. So will probably take out three of these, and do the ABC grind for a flat surface, waterjet from one a 7"ma ellipse, and with "net" help, hope to be able to successfully reasonably figure same.
Takes me back to my mid teens when the biggest scope I could locate, and buy in NZ (1961), was a 3" reflector I paid 17pounds 10shillings($35),which cost me a months wages, (farm hand) at the time. Also had a 2 1/2" refractor (used) 22pounds.($44). In those days the moto was, "if you cant get it, then you have to make it". As this was the only option, built my first 5 3/4"/7"(made two mirrors-the second the 7" mirror was really quite good to 50x per inch) EQ mounted Newt from the mirror up. Really things haven't changed that much, "necessity being the mother of invention".
Well you could make a sphere out of one of those blanks for testing the flat. I have thought about that myself. I have an old 8" f6 bk7 GSO mirror here that would be good for sacrificing for a secondary.
I just wanted to see if there are any active mirror makers in the Brisbane area. I have been following this and other forums for years and want to get back to my first project, a simple 6 inch mirror, before tackling something a bit more ambitious. Online advice is great, but it is also great to have a few other people to bounce ideas of and of course, as I live in a unit, tools and testing equipment are an issue.
Hi folks, great work Raymond with that mirror. Seems like we are all at that point of secondary mirror problems. I picked up a coffee table with a 14mm glass top from the tip for $5. It was immediately cut up for 4 diagonals. Like you folk, I also need to now explore flat making...
I just wanted to see if there are any active mirror makers in the Brisbane area. I have been following this and other forums for years and want to get back to my first project, a simple 6 inch mirror, before tackling something a bit more ambitious. Online advice is great, but it is also great to have a few other people to bounce ideas of and of course, as I live in a unit, tools and testing equipment are an issue.
Jimmy
Welcome Jimmy, there is a small Brisbane ATM group although it is having location problems at the moment. I am on the Sunny Coast, but get down to Brisbane now and then to the meeting. More details when the dust settles if you want.
Hi folks, I picked up a coffee table with a 14mm glass top from the tip for $5. It was immediately cut up for 4 diagonals. Like you folk, I also need to now explore flat making...
Hi Frank,
how did you get the diagonals cut? Were they cut at 45degs? I have been trying to figure out how to cut 7" minor axis diagonals, from 35mm thick plate glass. Would much prefer the 45deg angle cut, rather than waterjet cut on the flat.
how did you get the diagonals cut? Were they cut at 45degs? I have been trying to figure out how to cut 7" minor axis diagonals, from 35mm thick plate glass. Would much prefer the 45deg angle cut, rather than waterjet cut on the flat.
Best regards
Stephen
I have only rough cut them with the trusty angle grinder with diamond blade at this stage to about 145mm on the minor axis so as to have some in the middle that might be flat. I was then planning to cut closer to desired shape when polished, and then hand grind to final shape with the 45 deg. chamfer, hoping not to chip anything. I am very open to suggestions...
cheers Stephan,
Frank
What about setting the glass in plaster at 45deg then drilling it with a large round metal tube with silicon carbide and water. You would need a large drill press.
What about setting the glass in plaster at 45deg then drilling it with a large round metal tube with silicon carbide and water. You would need a large drill press.
Hi Raymond,
I have been thinking along the same line. I don't have a drill press, but have been looking at the possibility of getting one,(or access to), it would have to be large. Would be a long cut (7"x sq.rt 2),just shy of 10"(+thickness of glass x sq.rt 2), in all approx. 12" deep.
Problem solved. Managed to source a 7.2" minor axis 1/10 wave secondary locally. Very reasonably priced. Will be able to continue with the 33"f4 project and stay within my previous budget.
Nice job Raymond. Also nice pic of Saturn. Now you need to revise your signature, to include this scope. Again congratulations on finishing a great project. Still got more glass if you want a new project.
Hi all, thought I would let you know how the 18" of the 19" turned out. Had a problem star testing using Antares, as there seemed to be an optical defect that looked like a little blue star next to it. Turned out it was the Antares partner. I had no idea it was a double!
As for the silvering, it is a bit thin as I can just see through it so probably about 5nm thick, I think you need about 100nm to get a complete film.
On another subject there were terrible star test images showing triangular shaped star rings. This was caused by a wooden curved support for the lower part of the mirror. This has been replaced with a packing tape band to support the mirror and now stars are tack sharp, and Saturn looks like Raymond's pic. (Congrats Raymond, good effort). BTW I found a diag at Bintel suitable for f4.7, so allis well.
Excellent result. Just goes to show that an ATMer can grind, polish, and successfully figure a large aperture mirror to a high degree of accuracy "straight out of the blocks". There is so much help out there on the internet, for anyone who has the determination, and patience, to take on such a project. Again super effort.
cut? Were they cut at 45degs? I have been trying to figure out how to cut 7" minor axis diagonals, from 35mm thick plate glass. Would much prefer the 45deg angle cut, rather than waterjet cut on the flat.
priced. Will be able to continue with the 33"f4 project and stay within my previous budget. 
