self making reflector

[jkm13]

hi..

I heard someone make 16" reflector with firex glass. my wonder is this could be realize with just one man's hand?

i think this would be very precise curve.

can hand made would be good? and if yes, how?

thanks

[Chris]

Would this be the first Mirror you've ground, polished and figured? If so it's usually recommended to start out with something like an 8" f/6 and build up the difficulty level from there. 

It is possible to do a 16" mirror single handed, my astro club ground a 19" in the early 2000's. They needed to send it off to the professionals in the end due to zonal problems but they did the main bulk of the work with one pair of hands at a time. It's a very good scope now!

[Putaendo Patrick]

I've often heard it said that John Dobson used the glass from scrapped ship's portholes as blanks - perhaps just part of the myth?

[Astrobits]

20 minutes ago, Putaendo Patrick said:

I've often heard it said that John Dobson used the glass from scrapped ship's portholes as blanks - perhaps just part of the myth?

Old portholes were a good source of thick discs of glass for early mirror makers. With the invention of toughening treatments for glass, these were replaced with thinner glass that could not be used to grind mirrors as they were too thin and would shatter too easily. Also laminated glass was developed and is unsuitable for mirror makers as, again, it is usually too thin.

Plate glass, the old process of making glass sheets, would produce glass thicknesses well over 1" (25mm ), 1 3/4" ( 44mm ) being common. With toughening and laminating taking over the jobs which those thick glasses were used for, the plate glass process has been replaced with float glass and is not made any thicker than 1" now. The thicker glass for telescope mirrors has to be made specially for this dedicated market or sourced from other applications such as reactor vessel windows.

Nigel

[mikeDnight]

If you're going to try your hand at mirror making, definitely don't start with a large blank. Like Chris said, an 8" would be a far more manageable size to begin with. A 6" would be a better first project.

Start by reading Amateur Telescope Making books 1 & 2, and make a F8 or F10 scope. They are easier to figure more accurately than the shorter F ratios and will give pleasing results. 

Mike

[jkm13]

Thanks for all reply to this topic

@Main Sequence : it's amazing 19" could be done. thanks for suggest.

@mikeDnight : Thanks for suggestion.

i wonder is there a tip for precise grinding.

 

[Chris]

3 hours ago, jkm13 said:

Thanks for all reply to this topic

@Main Sequence : it's amazing 19" could be done. thanks for suggest.

@mikeDnight : Thanks for suggestion.

i wonder is there a tip for precise grinding.

 

Hi that's ok, my name is Chris not main sequence though (main sequence just relates to the post count e.g. you're nebula as you're just getting started on this forum)

 I'm no expert but have contemplated grinding a mirror quite a few times over the years. I read a book on the subject about 12 years ago, can't quite remember which? Generally you can learn a lot reading about the subject online, or watching videos online. Just do a Google search on grinding a telescope mirror and see what comes up....there's loadsof info out there on the web   

e.g. here's the master himself grinding a big mirror:

 

[Chris]

Darnit! Looking at videos online has perked up my interest....again...face-palm!   

[Skyline]

51 minutes ago, Chris Lock said:

Darnit! Looking at videos online has perked up my interest....again...face-palm!   

Go on, buy another scope chris !

[jkm13]

On 1/10/2017 at 18:32, Chris Lock said:

Hi that's ok, my name is Chris not main sequence though (main sequence just relates to the post count e.g. you're nebula as you're just getting started on this forum)

 I'm no expert but have contemplated grinding a mirror quite a few times over the years. I read a book on the subject about 12 years ago, can't quite remember which? Generally you can learn a lot reading about the subject online, or watching videos online. Just do a Google search on grinding a telescope mirror and see what comes up....there's loadsof info out there on the web   

e.g. here's the master himself grinding a big mirror:

 

hello Chris...

 

I'm sorry confusion your name and late reply.

i have forgot this thread.

Your link is what exactly i want to see. very appreciate!

it's really wonder human hand make this precise curve.