How to grind a mirror for a telescope
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- เผยแพร่เมื่อ 8 ส.ค. 2011
- How to grind a mirror blank into the well-figured basis for a Dobsonian telescope. How to grind the glass, how to carry out a focus test, how to polish with a pitch lap and how to find the focal point.
- วิทยาศาสตร์และเทคโนโลยี
My dad did exactly this procedure in the 60's when I was a lad. I was fascinated by the whole long process. I'd give pretty much anything to get that 8 inch mirror back -- it's long lost.
Did your family sell the telescope?
@@pavel9652 Dunno -- after several moves over the years it just was gone. My did may have sold or traded it for something...I'll never know.
I am glad to see the many different techniques which could be applied in making a mirror as I've never seen it done this way, but this tutorial, for being 40min long is absolutely one of the most difficult and poorly explained that I've seen for teaching a novice (I am not a novice, but I was when I began watching this 10 years ago).
Have you got any tutorial videos explaining the same process?... that we could view??...
What an absolute mad lad, building his own mirror, love a bit of backyard boffin.
Wow I can't wait to do this. Summer vacation project!!
ردxd
It’s been 7 years, how did it go?
Great video
You can do things differently. Use plaster (dental stone) or regular stuff, glue the tiles on with 2 part epoxy, and just use parts of whole tiles to fill the edges in. A grit sequence of 80g, 120 220, 320 500, and then 25 micron 15m, 8m 5m and 3m. The curve will change LITTLE after 220g, so at that point use it to cast a plaster tool to use for the pitch lap. dont worry about silicosis or overheating the blank as long as you work by hand and use enough water
Fantastic video. Many thaks. @21:50 the mirror does not seem to be covered in clingfilm. How do you get the film that tight on the mirror ? Bravo for this tutoril. Tom.
Amazing! 10 Thumbs up!
I customized my rotary sander / mounted and restricted it to the vertical plane and it works great. I appreciate your technique however it is costly and often dissapoints when mounted for gazing.
If you "dislike" this, you have no sense. If it wasn't for people like this, you'd still think the earth was flat, LOL.
ur an idiot...u dont belong here
@@seansoblixe9711 that guy died 2 years ago man , you 2 years 2 late
@Rcoders --- hilarious!
Aren't you supposed to keep water mixed with the grits so you don't inhale the dust?
nice
I feel a lot was left out of this video. I got the gist of it, but I am missing many details.
i want start now!!!🔭
also how long did this whole process take you?
How can this hand-technique even be precise?
A combination of very small, slow changes, and lots of testing and corrections.
Hand work being somewhat "random", so as long as you have the experience to avoid handing mistakes (too much or too less pressure, uneven grinding etc etc) you avoid the periodic errors a simple machine would make.
As for the Foucault test, while looking "primitive" and simplistic, it can actually indicate errors in the mirror shape that are a fraction of wavelength of light (nanometers). These can then be corrected on the pitch lap (as it is very slow).
After, it's all a question of what level of error the mirror-maker finds acceptable.
The aim isnt to outperform the Hubble though. The aim is to have fun in making a mirror and telescope. How well it performs in that role is then down to skill and dedication.
now where does one get such a piece of glass
true
How much mm thick mirror is this?
Hand grinding to match a perfect mathematics curving? Without any distortion. Don't know how does it possible?
Actually I wonder about the approach this guy uses. From what I know you're using either two glass plates or a grinding tool of a similar hardness. Then when grinding these two surfaces in an erratically pattern (so individual mistakes will even out) you will get two perfect spheres. Which one is concave is determined by the overhang. The parabolic shape then is created during the polishing process.How the here shown approach shall work out, I don't know.
Who's using the term mathematically perfect? Any physical object will never be perfect to the mathematical shape. It comes down to how much precision one wants or needs. Wagonwheels werent trying to be ideal circles, but they got the job done at the time.
Why did I just watch this...?
... well, at least I've learned something I guess.
What is the tool called that you are using to grind the grit into the lens?
Imaginatively, it’s know as the tool. Sometimes the grinding tool.
You can skip some grits and go 80 grit, 220g, 500 then 25 9 5 and then rough to polish by you need to spend more time on each step, so fewer steps but more time on each but good if you are missing some of the sequence.
You need to make SURE you've removed all the pits left behind by the previous step before moving on. ANY large pits will be very obvious by the time you get to 9 micron andf you won't be able to remove them without going back. To know how glass looks, grind glass tiles ith them
By "Wooden log splitting wedge" I assume you mean a carbon steel tool for the splitting of wood logs? Can you provide a link of where to buy one that is suitable? They seem to be 12 GBP from a local tool shop (but they have none in stock of course) and 9 GBP on Ebay. I suppose I need to ask whether the one I buy has a flat 2" x 1" section on the rear of it. I already bought the 205mm x 25mm Low Expansion (Schott Borofloat-33) blank from Stathis with zero internal strain (fully annealed) to ensure no astigmatism from the strain the glass itself ;- www.cloudynights.com/topic/394064-strain-testing-6-14-x-1-pyrex-mirror-blanks/page-4?hl=%2Bmirror+%2Bblank+%2Bstrain+%2Btest#entry5081696 and I have the 80 grit Silicon Carbide so I'm ready to start grinding.
Cooooooooooooooooool
He sounds very much like Dr. Poliakoff
Very difficult to follow. Seems to have many steps missing. Also, it seems the initial grinding by hand is largely little more than guess work. How can the concave arc being cut into the glass possibly be consistent? The video does not make sense.
Doesn't it make more sense and probably cheaper plus quicker to just use another glass blank? Buying concrete, grout, tiles ect would probably be more expensive and hassle especially for smaller mirrors (up to 200mm)?
Nice video I guess im just dont get testing the mirror. I watched a few different videos and it seems like it just gets a few seconds of mentioning.
@@Cris-vn8jl what?
When he slid that ruler across that mirror and made those screeching noises, I got shivers
@dylandd100 What's a better technique? I'm trying to make lenses of a much smaller diameter and thickness for my camera.
oh the humanity
can i use wood instead of timber?
Maybe it's wood for small mirrors and timber for larger mirrors...I'm new to this and not sure of the nomenclature.😕
can you send me the links so i can purchase.
Thank you Rob Brown
Hi im pretty new to this,but why do you call it a mirror and not a Primary lens
He's calling it a mirror because it is going to become a mirror after silvering it.
Assuming it's made for a telescope, then it's for a Newtonian Telescope (see wikipedia for details), which uses mirrors instead of lenses.
itai alter
Thanks
Is it possible to just buy mirrors for a telescope build?
It is. But people say it can be more expensive than just buying a new telescope. You can compare the prices for the diameter you are looking for and see for yourself I'm not sure.
It's also possible to buy a telescope. I assume this kit is for people that would WANT to grind their own, not so much the NEED.
Yes. But not cheap. At least not a finely figured one. The point of DIY is the satisfaction of having crafted a precision optic yourself. And with practice and patience, turn out a much higher quality than "reasonably priced" ones cranked out in mass production. There is no such thing as a perfect mirror. There is "good enough", better, way better, and exquisite. There is a point that further perfection ceases to be noticeable. Not sure, but I seem to recall somewhere around 1/12 wave or possibly more the performance curve begins to flatten out.
How to make a mirror with blue tac and a penny
Here they all show how to make a tool, but they don't tell the principle of how it polishes a mirror. Where can you find out about this?
Why is the tool flat and the mirror is spherical?
oh god the movie Earthquake is on and people are getting crushed by styrofoam buildings
i've watched a lot of these grinding videos and this one confuses the hell out of my tiny brain. why no small cheap blank of glass for the tool instead of all these strange shaped items?
Totally agree. I leave more confused than ever... and I have two years experience working in ATM workshops and my garage.
Has to do with cost and time. My first two scopes 6” & 10” were made with glass tool & mirror. Now glass is too expensive, my last one was plaster & dental squares, then rosin to polish.
Man has a hard time replicating what a computer can do!
right govnah,after grinding yul hear a hi pitched noise and that is your sanity dissipating
get some feeler guages
A taper gauge would have also been nice .
id save myself all this grief and just buy one !
I make my own pasta, I think I will save up a buy a mirror, however thanks for sharing that
You can make a drinking game from this vid-take a shot every time you hear the word "grind."
Seems to have been edited by a short attention spanned halfwit, so many details edited out, we wanted to hear everything he said.
ma che silicosi.Per un pò di polveretta? io lavoro da decenni legno e pietra,ho raggiunto i 60 anni,ho i polmoni senza problemi,non ho nemmeno mai ne raffreddori ne influenze.Fa peggio il traffico cittadino o ancora di più il fumo di sigaretta.
fuck that for a game of soldiers..
Barble.
oh my god don't break it
very poor method of explaing the process. you should have acomplished the various stages as you verbally explained